POWER SYSTEM COMMISSIONING AND MAINTENANCE PRACTICE

DET 310

CHAPTER 6

UNDERGROUND CABLES

60 INTRODUCTION

A considerable amount of transmission and distribution of electrical energy especially in densely populated urban areas is carried out by means of underground cable

The underground cable are rugged in construction and provide greater service reliability increased safety better appearance and trouble free service under a variety of environmental conditions

61 Applications Of Underground Cables

Underground cables are necessary for supply connection in the electrical plants in generating stations transmission system and distribution systems utilization plants and so on List of example of underground cable application for connecting one apparatus with the others for the following

- Supply power to the individual machine apparatus in electrical plants- Connection between switchgear and individual load group load- Connection between auxiliary transformer and switchgear- Subtransmission line between receiving substation and distribution substation

62 Underground Distribution System Vs Overhead Line

Safety Reliability of supply Interference Disturbance Maintenance Environment impact Economics

63 Cable Constructions

A cable consists of three main components-bull Conductorbull Insulationbull Sheath

External protection is provided by the sheath against

mechanical damage chemical reaction moisture an so on

63 Cable Construction (continue)-

bull Conductorndash An element design to

transmit electricityndash A single core has one

conductor while a three-core has 3 conductors

ndash A cable may be has single core 3 core or multiple conductor

04172023

6

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Insulationndash Is a material that reduces

or prevents the transmission of electricity

ndash Each conductor is covered by insulation

ndash Insulation is phase to ground and phase to phase

XLPE

PAPER

04172023

7

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Sheathndash Cable protective covering ndash Metallic or nonmetallic

protective covering over the conductor insulation shield

ndash External protection is provided by the sheath against mechanical damage chemical reaction moisture an so on

04172023

8

ETE503 Underground Cable

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

60 INTRODUCTION

A considerable amount of transmission and distribution of electrical energy especially in densely populated urban areas is carried out by means of underground cable

The underground cable are rugged in construction and provide greater service reliability increased safety better appearance and trouble free service under a variety of environmental conditions

61 Applications Of Underground Cables

Underground cables are necessary for supply connection in the electrical plants in generating stations transmission system and distribution systems utilization plants and so on List of example of underground cable application for connecting one apparatus with the others for the following

- Supply power to the individual machine apparatus in electrical plants- Connection between switchgear and individual load group load- Connection between auxiliary transformer and switchgear- Subtransmission line between receiving substation and distribution substation

62 Underground Distribution System Vs Overhead Line

Safety Reliability of supply Interference Disturbance Maintenance Environment impact Economics

63 Cable Constructions

A cable consists of three main components-bull Conductorbull Insulationbull Sheath

External protection is provided by the sheath against

mechanical damage chemical reaction moisture an so on

63 Cable Construction (continue)-

bull Conductorndash An element design to

transmit electricityndash A single core has one

conductor while a three-core has 3 conductors

ndash A cable may be has single core 3 core or multiple conductor

04172023

6

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Insulationndash Is a material that reduces

or prevents the transmission of electricity

ndash Each conductor is covered by insulation

ndash Insulation is phase to ground and phase to phase

XLPE

PAPER

04172023

7

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Sheathndash Cable protective covering ndash Metallic or nonmetallic

protective covering over the conductor insulation shield

ndash External protection is provided by the sheath against mechanical damage chemical reaction moisture an so on

04172023

8

ETE503 Underground Cable

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

61 Applications Of Underground Cables

Underground cables are necessary for supply connection in the electrical plants in generating stations transmission system and distribution systems utilization plants and so on List of example of underground cable application for connecting one apparatus with the others for the following

- Supply power to the individual machine apparatus in electrical plants- Connection between switchgear and individual load group load- Connection between auxiliary transformer and switchgear- Subtransmission line between receiving substation and distribution substation

62 Underground Distribution System Vs Overhead Line

Safety Reliability of supply Interference Disturbance Maintenance Environment impact Economics

63 Cable Constructions

A cable consists of three main components-bull Conductorbull Insulationbull Sheath

External protection is provided by the sheath against

mechanical damage chemical reaction moisture an so on

63 Cable Construction (continue)-

bull Conductorndash An element design to

transmit electricityndash A single core has one

conductor while a three-core has 3 conductors

ndash A cable may be has single core 3 core or multiple conductor

04172023

6

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Insulationndash Is a material that reduces

or prevents the transmission of electricity

ndash Each conductor is covered by insulation

ndash Insulation is phase to ground and phase to phase

XLPE

PAPER

04172023

7

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Sheathndash Cable protective covering ndash Metallic or nonmetallic

protective covering over the conductor insulation shield

ndash External protection is provided by the sheath against mechanical damage chemical reaction moisture an so on

04172023

8

ETE503 Underground Cable

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

62 Underground Distribution System Vs Overhead Line

Safety Reliability of supply Interference Disturbance Maintenance Environment impact Economics

63 Cable Constructions

A cable consists of three main components-bull Conductorbull Insulationbull Sheath

External protection is provided by the sheath against

mechanical damage chemical reaction moisture an so on

63 Cable Construction (continue)-

bull Conductorndash An element design to

transmit electricityndash A single core has one

conductor while a three-core has 3 conductors

ndash A cable may be has single core 3 core or multiple conductor

04172023

6

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Insulationndash Is a material that reduces

or prevents the transmission of electricity

ndash Each conductor is covered by insulation

ndash Insulation is phase to ground and phase to phase

XLPE

PAPER

04172023

7

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Sheathndash Cable protective covering ndash Metallic or nonmetallic

protective covering over the conductor insulation shield

ndash External protection is provided by the sheath against mechanical damage chemical reaction moisture an so on

04172023

8

ETE503 Underground Cable

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

63 Cable Constructions

A cable consists of three main components-bull Conductorbull Insulationbull Sheath

External protection is provided by the sheath against

mechanical damage chemical reaction moisture an so on

63 Cable Construction (continue)-

bull Conductorndash An element design to

transmit electricityndash A single core has one

conductor while a three-core has 3 conductors

ndash A cable may be has single core 3 core or multiple conductor

04172023

6

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Insulationndash Is a material that reduces

or prevents the transmission of electricity

ndash Each conductor is covered by insulation

ndash Insulation is phase to ground and phase to phase

XLPE

PAPER

04172023

7

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Sheathndash Cable protective covering ndash Metallic or nonmetallic

protective covering over the conductor insulation shield

ndash External protection is provided by the sheath against mechanical damage chemical reaction moisture an so on

04172023

8

ETE503 Underground Cable

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

63 Cable Construction (continue)-

bull Conductorndash An element design to

transmit electricityndash A single core has one

conductor while a three-core has 3 conductors

ndash A cable may be has single core 3 core or multiple conductor

04172023

6

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Insulationndash Is a material that reduces

or prevents the transmission of electricity

ndash Each conductor is covered by insulation

ndash Insulation is phase to ground and phase to phase

XLPE

PAPER

04172023

7

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Sheathndash Cable protective covering ndash Metallic or nonmetallic

protective covering over the conductor insulation shield

ndash External protection is provided by the sheath against mechanical damage chemical reaction moisture an so on

04172023

8

ETE503 Underground Cable

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

63 Cable Construction (continue)-

bull Insulationndash Is a material that reduces

or prevents the transmission of electricity

ndash Each conductor is covered by insulation

ndash Insulation is phase to ground and phase to phase

XLPE

PAPER

04172023

7

ETE503 Underground Cable

63 Cable Construction (continue)-

bull Sheathndash Cable protective covering ndash Metallic or nonmetallic

protective covering over the conductor insulation shield

ndash External protection is provided by the sheath against mechanical damage chemical reaction moisture an so on

04172023

8

ETE503 Underground Cable

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

63 Cable Construction (continue)-

bull Sheathndash Cable protective covering ndash Metallic or nonmetallic

protective covering over the conductor insulation shield

ndash External protection is provided by the sheath against mechanical damage chemical reaction moisture an so on

04172023

8

ETE503 Underground Cable

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

64 Types of Underground Cables

bullThe identification of the cable are based on the several items

bull Insulationbull Voltage Systembull Cable Sizing And Corebull Technical Specification Characteristics Of The

Cable

9

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

64 Types of Underground Cables (continue)-

bullUsually the operating voltage decides the types of insulation and cable placed in various categories depending upon the voltage for which they are designed

ndashLow Voltage Cable (LV) 11kVndashHigh Voltage Cable (HV) 11 kV

10

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

64 Types of Underground Cables (continue)-

bullPaper Insulationndash3 core belted 11kV PILC cablendashSingle core screened 11 kV PILC cable

bullPolymer Insulationndash3 core XLPE 11 kV cablendashSingle core XLPE 11 kV cable

11

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

64 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (carbon black paper )bull C = Insulation (Paper)bull D = Insulation Screen

(carbon black paper)bull E = Sheath (copper

lead)bull F = Jacket

Example of Single core screened 11 kV PILC cable

12

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

65 Types of Underground Cables (continue)-

bull A = Conductor (Aluminum)

bull B = Strand Screen (extruded

semiconducting)bull C = Insulation (XLPE)bull D = Insulation Screen (extruded

semiconducting)bull E = Shield (copper

tape)bull F = Jacket Example of Single core

XLPE 11 kV cable

13

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

65 Types of Underground Cables (continue)-

ndash Excellent Electrical amp Physical Properties

ndash Capable Of Carrying Large Current At High Temperaturebull Normal ~ 90ocbull Emergency ~ 130ocbull Short Circuit Conditions

~250ocndash Easy To Install ndash XLPE Easier

To Jointndash No Need For Metallic Sheath

14

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

66 (CABLE FAULT) INTRODUCTION

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

1048707 Cable faults are undesirable causes because-

1 Power supply is interrupted

2 Locating fault in a long underground cable is difficult and time consuming

3 Repairing faulty cable is difficult and time consuming

66 Cable Fault Introduction (continue)-

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

662 CAUSES OF UNDERGROUND CABLE FAILURE

Major factors that cause failure of a cable are-

bull Damaged accidentally by external mechanical means

bull Damage caused as a results of mishandling the cable

during layout

bull Poor workmanship in cable jointing

bull Natural causes due to aging

of cable

bull Damaged caused by movement

of soil and erosion

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

661 MECHANICAL

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

663 MISHANDLING

Mishandling of cable may be occurred during installation

Some of the examples are

1 Excessive pull

2 Sharp bend

3 Accident crush

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

664 Poor workmanship During Cable Jointing

The cable are jointed together with poor workmanship can lead to cable fault after a period of time

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

665 NATURAL CAUSES DUE TO AGING OF CABLE

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

CONTINUE-

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

CONTINUE-

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

66 TYPES OF CABLE FAULT

GENERAL

bull Series (open circuit) Fault

- Failure of continuity (conductor (s) or cable)

bull Shunt (short circuit) fault

- failure of insulation

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

66 TYPES OF FAULT (CONTINUE)-

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

66 TYPES OF FAULT (CONTINUE)-

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

661 SERIES AND SHUNT FAULT

Are subsided into the following categories

Low Resistance Faultof ZR 10

Where Zo= cable surge impedance

=10 ndash 100 ohm

Usually happens in series fault

High Resistance Fault

Where ZoR f 10

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

662 INTERMITTENT OR FLASH FAULT

- Usually not apparent to insulation resistance measuring

instrument

- Does not manifest itself at lower voltages or a surge

- Breakdown will appear under application of high voltage

dc or DC pressure test

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

67 FAULT LOCATION PROCEDURE

The proper sequence of cable fault location are as follows

a) Analysis of fault

b) Pre-location

c) Pin Pointing

d) Confirmation and re-test

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

671 Analysis of Cable Fault

To analyze a cable fault is to determine and confirm the nature or characteristics of the fault

Objective to select which of the cable fault locator equipment of method is best suited to locate the particular fault

Analysis of cable fault normally consists of insulation resistance test and continuity test carried out using 1000V or 5000 V insulation tester

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

671 Insulation Resistance test

With all earth connections removed from the cable conductor terminal using IR tester of 100025005000V range measure and record the IR in M-ohms K-ohms or ohms between conductors and between conductors and earth Six measurement are to be taken R-E Y-E B-E R-Y Y-B B-R An IR of 100M-ohm indicates a healthy cable

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

672 Continuity Test

With the cable conductor looped or shorted at the tail endremote end using IR tester selected at continuity range perform continuity test

This test will determine whether any of the cable is open circuited

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

672 Continuity test (cont-)

Continuity Test - With the cable conductor shorted or looped at the remote end perform continuity test on the cable

- Measure and record the results in ohm

- Three measurements are to be carried out between R-Y Y-B B-R

- The test will determine whether any of cable is open circuited - The resistance per-conductor per km is provided in Table VI VII VIII and IX (refer appendix A)

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

672 (cont-)

if the continuity of the cable is sound insulation resistance from one end are sufficient

If continuity is broken IR test should be carried out at both ends of the cable

68 BURNING A FAULT

The continuity and IR test may indicate that burning of fault by means of HT pressure test set is required

-

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

68 BURNING A FAULT (continue-)

Burning a fault is achieve by passing current from a DC HT test set through the fault

Other conductors not under test should be earthed

HT is applied for about 5 to 10 minutes to burn the fault

HT test is used to determine which fault location equipment is suitable to be used

HT is the last resort often used because it sometimes produce ambiguous and unpredictable results

Therefore fault location equipment should be attempted first

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

69 Pre- Location of fault

Pre-location is the application of a test at the terminals of a

given cable to give an indication of the distance to the fault

from the test point

Whilst the measurement should be accurate as condition will

allow the primary purpose of pre-location is to give an

indication as quick as possible of the vicinity in which to

commence the final pin-pointing tests

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

69 Pre- Location of fault (cont)-

Generally there are four pre-location methods which are practised and the are as follows

1Bridge or loop Method2 Pulse Echo Time Domain Reflectometry (TDR) method3 Impulse Current Method4 Arc Reflection and secondary Impulse method

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

691 Bridge method

6911 Direct reading fault localizer

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should not be more then 20 k-ohm

iii) Applied voltage not to exceed 600 V (DC)

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Case 1 Single conductor to earth with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Case2 Conductor to conductor with sound core available

Fault distance from front end X= n100 x L

Where n = localiser reading in

L= Cable route length

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Case 3 Three phase fault

By Open loop test and close loop test

(i) Rf2Rf1 gt 5 and (ii) Rf2 lt 20 k-ohm

Open loop test

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Case 3 Three phase fault

Close loop test

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Open loop and close loop test (cont)

Fault distance from front end

Lxm

mn

X 2

1001

)200200

(

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

High Tension Bridge

Conditions required

i) No break in continuity if possible one sound core available

ii) The fault resistance of cable should be more then 20 k-ohm

iii) Applied voltage not to exceed 20kV (DC)

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

High Tension Bridge

Case 1Single Conductor to earth with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

High Tension Bridge

Case 2Conductor to conductor with sound core available

Fault Distance from test end X = n100 x 2L

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

High Tension Bridge

Case 3Three phase Fault with no sound core available

Rf2Rf1gt5 Rf2gt20 kohm

Lxm

)mn

(X 2

1002

1

100100

Where m = open loop bridge reading

n = close loop bridge reading

L = cable route length

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6912 Universal Bridge to measure capacitance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be more then 100 ohm

iii) Earth all the conductors not under test

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6912 Universal Bridge to measure capacitance of Cable

Open circuit with sound core available

Fault Distance from test end x = CA x L CAB

CA = Capacitance of open circuited coreCAB = Capacitance of sound coreL = conductor length

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6912 Universal Bridge to measure capacitance of Cable

Open circuit with no sound core available

Fault Distance from test endfront end = ((CA(CA+CB))x L

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6913 Universal Bridge to measure Inductance of Cable

Requirement

i) Open Circuit Fault

ii) Fault resistance of cable should be less then 30 ohm

iii) All conductors be left free from earth

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6913 Universal Bridge to measure Inductance of Cable

Open circuited with sound core available

Fault distance X = LA x L LAB

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6913 Universal Bridge to measure Inductance of Cable

Open circuited with no sound core available

Fault distance X = LA x L LA + LB

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

692 Pulse Echo (PE) Time Domain Reflectometry (TDR)

A simple method which works on travelling wave principles It is applicable to all series and shunt faults with Rf gt=Zo10 (5 ohm) and Rflt=10 Zo (500 ohm) respectively For power cables typical Zo=50 ohm

6921 Travelling wave principles

A pulse injected into a cable is reflected back to the source by any change in characteristics impedance (Zo) of the cable

The waveform generated can be monitored using an oscilloscope as shown in Figure below

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6921 Continue-

Waveform interpretion

Shunt Fault

Series Fault

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6921 Continue-

Waveform interpretion

Low Resistance Shunt Fault (Rflt=500 Ohm)

-Reflection Negative

-Amplitude depends on fault resistance

Series Fault (Rfgt=5 ohm)

- Reflection Positive

- Amplitude depends on fault resistance

Zo = Characteristics impedance = radic(LC)

L = Inductance of cable C = Capacitance of Cable

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

69211 Reflection Factor (r)

- Is to determine the degree of reflection

Shunt fault r (V) = -Zo1(2Rf + Zo1)

Series Fault r (V) = Rf(2Zo1 + Rf)

Example shunt fault fault resistance = 5 ohm Zo = 50 ohm

r(V) = -50 (2 x5 +50) = - 833If fault resistance = 500 ohm

r(V) = -50 (2x 500 + 50) = -475

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

69212 Velocity of Propagation (Vp)

- Vp depends on the cable dielectric and is defined as

Vp = Vs radicEr

- where Vs = Velocity of light in free space

Er = Relative permittivity of dielectric

Vp = 300radicEr

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Dielectrics Velocity of PropagationVp (mmicroS)

Impregnated Paper 150 -171

PVC 152-175

PE Approx 200

XLPE 156-176

Typical Vp for different Dielectric

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

69212 Continue (Vp)

Example

Determine the velocity of propagation Vp2 for a cable length of 2500 meters t1= 3164 S and t2 = 1745 S Calculate the fault distances

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6921 Continue-

The distance to the fault Lf (m) is given by

Lf = T x Vp2

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

6921 Continue

Solutions

Velocity of propagation = Vp2 = 25003164 = 79 mS

Distance of Fault from test end = Vp2 x t2

= 79 x 1745

= 137855

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

693 Impulse Current Method

Working on Travelling wave principles it is applicable to all types of fault

694 Arc Reflection or Secondary Impulse method

Basically PE and TDR associated with fault treatment It is also applicable to faults of all nature but with easily interpreted breakdown waveforms

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

610 PIN POINTING

Pin Pointing is the application of a test that positively confirms the exact position of the fault

Before the commencement of pin pointing the prelocated fault distance should mark on the cable route which is measured by means of a trumeter

Pin pointing is normally carried out by the shock wave discharge method The fault can be detected by the use of semisphone

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

611 Confirmation and Re-Test

After the pin-pointed position of the fault has been marked and exposed check for physical sign of fault If there is the fault is confirm

After confirmation the fault should be cut away IR and continuity test should be carried out on the remaining cable sections to determine the soundeness of these cable sections

The insulation resistance test are again carried out after jointing followed by pressure test before supply can be restored

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Flowchart for Fault location Procedure

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Example

Find a fault distance using direct reading fault localiser from end test which has a test data as below

Bridge Balance Reading =60 Length of Cable 140 meters

Solutions

Fault Distance= = 60100 x 140 = 84 meterxL

n

100

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

For cables route with combination of 2 or more different type of cable

Determine the resistance of cable for each section separately from Table 1 and Table 2

Example Cable 11kV Al Length 150 m size = 16mm2

From Table 1= Resistance for 1km =226 ohm

For 150 m = 1501000 x 226 = 0339 ohm

From Table 1 Calculate the equivalent resistance for all the combined section

Example for Al = 0339 ohm for copper = 0150 ohm

Equivalent Resistance = 0339+0150 =0489 ohm

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Continue

Calculate equivalent resistance from obtained bridge reading

Example Bridge Reading = 60

Equivalent resistance = 06 x 0489 ohm = 02934 ohm

Determine which section of cable the fault occurs

Total resistance at Al section = 0339 ohm

As equivalent resistance at Al section is higher then 02934(Equivalent resistance from bridge test) the fault is

located at Aluminium section of cable

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Table 1 Impedance data for 635011000 V Cable Aluminium

Table II Impedance data 11000 V Cable Copper

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

TABLE VI ndash 6001000V (ALUMINIUM)

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

TABLE VII ndash 38006600V (ALUMINIUM)

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

TABLE VIII- 635011000 (ALUMINIUM)

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

TABLE V

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

610 COMMISSIONING OF UNDERGROUND CABLE

High Voltage DC testing

High voltage testing is carried out in order to determine the electrical strength of cable insulation Site tests are performed by applying a predetermined high voltage to the insulation DC site test voltages regardless of insulation type are used to ensure that the cable cable joints and termination are correctly made and installed

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

High Voltage Testing (cont-)

IEC Standards specify maintenance tests after installation should be 70 of permissible factory test DC voltages (15 minutes) = 175kV

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84

Insulation Resistance Test (cont-)

Test voltages should be slowly raised to the required value over a period of about 1 minute and the test period starts once the full voltage is reached In this way the capacitive and absorption currents will have decreased and circuit conditions stabilized such that true leakage current may be measured

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• 63 Cable Construction (continue)-
• 63 Cable Construction (continue)- (2)
• 63 Cable Construction (continue)- (3)
• 64 Types of Underground Cables
• 64 Types of Underground Cables (continue)-
• 64 Types of Underground Cables (continue)- (2)
• 64 Types of Underground Cables (continue)- (3)
• 65 Types of Underground Cables (continue)-
• 65 Types of Underground Cables (continue)- (2)
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44
• Slide 45
• Slide 46
• Slide 47
• Slide 48
• Slide 49
• Slide 50
• Slide 51
• Slide 52
• Slide 53
• Slide 54
• Slide 55
• Slide 56
• Slide 57
• Slide 58
• Slide 59
• Slide 60
• Slide 61
• Slide 62
• Slide 63
• Slide 64
• Slide 65
• Slide 66
• Slide 67
• Slide 68
• Slide 69
• Slide 70
• Slide 71
• Slide 72
• Slide 73
• Slide 74
• Slide 75
• Slide 76
• Slide 77
• Slide 78
• Slide 79
• Slide 80
• Slide 81
• Slide 82
• Slide 83
• Slide 84