APPA-Module 7-Protection & Coordination

Module 7

Power System Review Course

Protection & Coordination

By: Dr. Hamid Jaffari

Fuse

Transformer

Typical Distribution System

FOAKVA

FAKVA

OAKVA

%)135(000,10

%)125(9375

7500

FOAKVA

FAKVA

OAKVA

%)135(000,10

%)125(9375

7500


System Protection Instrumentaion

Principals of Protection

Protection Devices (Circuit breakers, Reclosers,

Fuses)

Principals of Coordination

Coordination Study

Fuse-Fuse Coordination

Recloser-Recloser Coordination

Recloser-Fuse Coordination

Relay-Recloser-Fuse Coordination

Power System Review

System Protection

Components

Instrument Transformers

PTs

CTs

Circuit Breakers & Relays

Mechanical

Digital

Reclosers

Fuses

Power System Review

Protective Devices Characteristics

Breaker: Distribution Class 12 kA<Isymmetrical Rating<20 kA Transmission Class> 50 kA Extinguishing arc by means of:

Oil, air blast, sulfur hexafluoride gas (sF6), vacuum, or simple arc chutes

Recloser: 4 kA< Isymmetrical Rating<12 kA Interrupting occurs in Oil or vacuum Designed to “reclose” after fault is cleared

Sectionalizers: interrupting capability<10KA Master minded by Reclosers

Power System Review

Protective Devices Characteristics

Expulsion Fuses: Typically 8 kA to 16 kA Subject to X/R (interrupting capability decreases as ↑ X/R )

Power Fuse are generally available for Operating Voltage <169KV with 15KA<X/R<25KA

Distribution Fuse are generally good for Operating Voltage<40K with 5KA<X/R<15KA

less accurate, inexpensive, but effective.

Current limiting fuses (CLFs) As much as 50 kA May have minimum interrupting capability, additional

protection may be needed

Oil switches: limited current interrupting capability.

Power System Review

Fault calculations

Note: I-fault drops off as inverse of Distance 1/d

Power System Review

Principals of Protective Devices

Definition of Protective Devices: Protective

Devices have Time-Current, Time-Voltage, or

Time-Frequency Characteristics

Protective Devices are responsible for

removing undesired conditions:

Voltage

Current

Frequency

Power System Review

What is the purpose?

Clear Temporary faults and restore power

when possible.

Interrupt Permanent Faults and Lock Out

Interrupt Faults in Proper Sequence

Remove undesired power conditions to

maintain:

Steady State

Stability

Power System Review

EPRI Fault Study

Faults Percentage

Phase-to-Ground 65%

Phase-to-Phase 11%

Phase-Phase to Ground 2%

Three Phase 2%

One Phase on the Ground 15%

Two Phase on the Ground 2%

Others 3%

Power System Review


What is Coordination?

Definition: Proper trip sequencing of protective devices

to isolate the fault and minimizing outage. This means

proper coordination between time and current curves

during power system abnormal conditions.

Coordination is :

1/3 Science

1/3 Art

1/3 Luck

Coordination

Protective Devices with Time-Current characteristics are:

Relays, Reclosers, Fault Interrupters, and Fuses.

How about Sectionalizers??

Device Relay Recloser FI Fuse

Relay Relay-Relay Relay-Recloser Relay-FI Relay-Fuse

Recloser Recloser-Relay Recloser-Recloser Recloser Recloser-Fuse

FI FI-Relay FI-Recloser FI-FI FI-Fuse

Fuse Fuse-Relay Fuse-Recloser Fuse-FI Fuse-Fuse

Fuse-Fuse

Coordination

Fuse Selection Process

Fuse Type/Class

Expulsion(Dist, Substation, etc)

CLF

Voltage Class

Fuse Isymm interrupting capability rating

X/R ratio

Fuse continuous current rating

i.e. K(150%), T(150%), QA(100%)

Fuse Application Fuses are generally:

CLF-used for short-circuit protection

Non-CLF or Expulsion Fuse is used for

Overload protection

Selection Criteria:

Non-CLF: 140% of full load

CLF: 150% of full load

Expulsion Fuse

%

100

ZxII loadfullsc

Fuse Clearing Time

@1/2 cycle

Zero Crossing

Transient Voltage

@

Clearing time

CT = MT+ Arcing Time

Current Limiting Fuse(CLF)

B

Curtsey of www.littlefuse.com

60,000 A

7,400 A

Fuse Types & Porperties

Fuse has two TCC curves

Minimum Melting

Total Clearing

Common fuse types through 27kV are:

Slow: T

Fast: K

Avoid mixing different type fuses for better coordination

Skip at least a size in each fuse class (K, T, H, C, etc)

for better coordination between two fuses(i.e. 20K, 40K,

65K, etc)

Power System Review

Fusing Philosophy

Lateral tap fuse selection Criterion:

I lateral= 2x ILoad

Cold load

Daily/monthly/Seasonal cyclic Load

Peak load

Transformer Fuse Selection Criterion:

Minimum Fuse Size= Irated x 1.2

Cold Load

Inrush Current

Operational Limits

Power System Review

Fuse Speed & Continuous Rating

Fuse Allowable

Continuous

current

Rating(%)

K-tin 150%

K-silver 100%

N 100%

T 150%

QA 100%

S 150%

Fuse speed from fast to slow → N>QA>K>T>S

Power System Review

Fusing Distribution Transformers

Why? In order to protect the transformer against

internal faults, downstream bolted faults, high

impedance secondary faults.

Fuse must withstand transient surge currents

caused by lightening, XFMR magnetizing inrush

current, and cold-load pickup. Therefore, fuse

must be capable of handling:

Cold Load Pickup

Inrush Current

Power System Review

Dist Transformer using…continued

Steps to select XFMR fuse size:

1. Calculate Cold Load Pickup withstand level:

1. I cold-load= 3 x I (full load for 10 seconds)

2. Calculate Inrush Current withstand limits:

1. I inrush= 12 x I (Full Load for 0.1 seconds)

2. I inrush= 25 x I (full load for .01 seconds)

3. Select the nearest primary fuse rating that: 1. Starts with 120% of XFMR rated load: Minimum Fuse Size = IRated x 1.2

2. Meets the Cold load & Inrush Requirements (Steps 1 &2)

4. Select the Fuse type (K, T,H, QA,etc) and coordinate it

with upstream & downstream fuses in service. Note: Using EEI-NEMA type K, T, and T Fuses Provides

protection between 200% to 300% of Rated Load

Power System Review

Example: Determine the minimum size fuse for

a 300 KVA, 13.8kV/277/480 volts XFMR using

“K” type fuse?

AmpkVx

KVAI loadfull 55.12

9.23

300

8.133

300

AmpxI SecloadCold 65.3755.12310@

AmpxI SecInrush 6.15055.12121.0@

AmpxI Secinrush 75.31355.122501.@

?%)160(20?%)120(15: KORKFuseMinimum

Transformer Fusing…continued

Power System Review

Transformer Fusing…continued

Power System Review

Problem Area

Substation Transformer Protection

Plot XFMR operational limits:

Thermal & Mechanical limits (Damage Curve).

Use FA Rating for XFMR Damage Curve Plot

XFMR Inrush &Cold-Load pickup.

Apply applicable NEMA & IEEE Standards:

IEEE C57.109-1993 oil immersed XFMR

IEEE C57.12.59-2001 dry-type XFMR

Example:

FOAKVA

FAKVA

OAKVA

%)135(000,10

%)125(9375

7500%6

16.4/86.22

Z

kVkV

Power System Review

Transformer Operating Limitations

t(sec)

I (pu)

Thermal 200

2.5

I2t = 1250

2

25 Isc

Mechanical

K=(1/Z)2t

(D-D LL) 0.87

(D-R LG) 0.58

Frequent Fault

Infrequent Fault

Inrush

FLA

Power System Review

Devices’ Damage Curves

t

Time

I-Current

I2

2t

Gen

I2t

Motor Xfmr

I2t

Cable

I2t

Power System Review

=Let-through Energy I2t

Transformer Prim Fuse Protection

Capacitor Fusing Capacitor fuse must be between 135% to 165% of its

full load current rating depending on manufacturer.

Example: Find appropriate fuse size for a 1800 KVAR

cap bank installed on a 22.86kV line.

65.1

35.1

xLoadFullFuseCapacitor

or

xLoadFullFuseCapacitor

AmpkVx

KVARI loadfull 5.45

6.39

1800

86.223

1800

FuseQAorKSelect

AmpFuse

FuseCapacitor

6050

5.40

35.1*5.455.1*

Note: Check fuse continuous/overload capability (100%-150%)


Fuse-fuse coordination must follow the following

rule:

Desirable coordination: Time Ratio of two fuses

Must Not Exceed the 75% Ratio

%75)(

)(

fuseupstreamMT

fusestreamdownCTofRatioTime

Time

limiton coordinati

MT) of (75%A Fuse

Current

A of MT

B of CT

A CTof

Fuse

A B

Source

Fault

LoadFuse

Power System Review

75.0*)()( upstreamMTfusestreamdownCT tt


Example: What is the minimum size fuse that

coordinates with 50K lateral tap fuse if calculated

fault current is 1000Amp at point B?

MT(A Fuse)=0.051 sec for Fault Current @ 1000

Amp

75.0)(

)(

AfuseupstreamMT

BfusestreamdownCT

051.075.075.0051.

)(xCT

BfusestreamdownCT

sec038.0CT

K50

K?amp26

ampI G 1000

BA

Power System Review

50K Fuse-20K Fuse Coordination

Coordination Limit

K50

K20amp26

ampI G 1000

BA


Example: Select a fuse size at point C That can

achieve proper coordination with upstream fuses.

K65

K?amp35

ampI Maxfault 1000

B

A

K100

C

amp90

ampI Maxfault 2000

ampI Maxfault 1500

amp80

Power System Review

Fuse-Fuse coordination

K65

K?

amp35

ampI Maxfault 1000

B

A

K100

C

amp90

ampI Maxfault 2000

ampI Maxfault 1500

amp80

Recloser-Fuse

Coordination

Recloser Defined in ANSI/IEEE C37.60

Settings Require Selecting:

Minimum Pick up or Coil size

Curve Selection:

Fast Curve

Slow Curve

Operating Sequence:

Number of Fast Curve shots

Number of Slow Curve shots

Shots to lockout

Reset time

Power System Review

Recloser

Two Types:

Hydraulic

Minimum Pickup is done by selecting appropriate rating for

Series Coil inside the tank

TCC Curve Selection & Settings are done inside the tank

Electronics

Minimum Pickup: Trip Resistors

TCC Curves and Timing plugs are done at the front panel

Control

Hydraulic

Solid State

Microprocessor

Power System Review

Electronic Recloser Settings

TCC Curve

Curve Selection/Type

Settings:

Min Trip Setting

Phase & Ground

Instantaneous Trip Setting

Phase & ground

Constant Time Adder

Amp Multiplier

Reclosing Operation Setting

Typically Two Fast/Two Delay

0.5 sec<Reclosing intervals<60 sec

Power System Review

Electronic Recloser Settings

Phase Trip Setting

Minimum Trip= (Range of 2 to 2.5) x Max Load Current

This facilitates cold load pick up & load growth

Ground Trip Setting

Minimum Trip= (Range of 0.3 to 0.5)x Phase Minimum Trip

Min trip setting helps to protect against high impedance faults

Instantaneous Setting

Trip Setting= (Range of 4 to 16)X Minimum Trip

Power System Review

Hydraulic Recloser Phase Trip-Setting

Estimate the Peak load

Determine the Coil Size:

Inrush Current dictates the coil rating selection

Coil Size(Amp)=1.25 x Peak Load

Calculate the Minimum Phase Trip Setting:

Minimum Trip(Amp)=2 x Peak-Load

Some utilities use factor of 2.5 or 3.0

Example (W type Hydraulic Recloser; coil sizes are 100, 140, 200, 280,

400, and 560):

Assume Peak Load= 150A

Coil Size= 1.25 x 150= 187.5→ Thus select 200 A

Minimum Trip= 2x150= 300A→ Select 400A Min Trip Level

(Note: 200A Coil has Minimum Trip Rating of 400A)

Power System Review

Hydraulic Recloser Ground Trip-Setting

Steps:

1. Calculate the Normal Load Unbalance

2. Calculate the end-of-line minimum fault current level.

The Iground-Trip must be bellow Imin-Fault.

3. Estimate the Ground Minimum Trip Level.

LoadPeakofII %10UnbalanceLoadNormal1

faultMinLineofEndTripMinground II

Device)PhaseSingleLargestthebyCreatedUnbalanceLoad(2Unbalance)LoadNormal(1 III TripMinground

Fuse(Amp)TapLargetsUnbalanceLoadLargest2 II

faultMinLineofEndTripMingroundLoadUnbalance IIIII )( 21

Power System Review

Recloser-Reloser

Hydrolic Reclosers:

Min Trip and continuous current are both dependent of the coil size

Reclosing intervals are 1, 1.5, and 2 seconds

Small Reclosers have Series coil : H, VH, L, and E series

TCC Curve Separation >12 Cycles (0.2 sec); typically 0.25-0.30 sec

Large Reclosers have High-Voltage solenoid : D, V, W, VW series

TCC Curve Separation > 8 Cycles(0.133 sec); typically 0.2 sec

Electronic Reclosers:

Unlike Hydraulic recloses, Min Trip is independent of the Recloser’s

continuous rating

Reclosing intervals are 2, 5, and 15 seconds

Min Trip selection must allow for the cold-load pick up & load growth

TCC Curve Separation > 0.30 Sec

0.30 Sec=0.22 sec (CT saturation& errors)+0.08 sec (Breaker Opening time)

TCC Coordination Time Margins

TCC Coordination Time Margins

Electronic Recloser to Hydraulic Recloser:

TCC Curve Separation > 0.2 Sec; typically 0.25 sec

Recloser-Fuse

Methode#1: Use K factor for Recsloser: Range of

1.25<K<1.8

Methode#2: ADD Recloser Cumulative Times

Add the cumulative reclose interval for a 2A-2C recloser sequence and coordinate with Fuse

Minimum Clearing curve x 0.75

Power System Review


Recloser Cumulative Time Method

<Coordination Limit <

Temp Fault:

Recloser operates; Fuse

is saved.

Permanent Fault:

Recloser operates first,

then fuse blows

Current

Time

delay BBA 22B'

'a'ba b

A2A' Fast)(A

curve) damage (fuse curve MT fuse of %75

R

Fuse

'a'b

Power System Review


K-Factor Method

<Coordination Limit<

Refer to Manufacturer’s

Supplied Tables

Extract applicable K-Factor

Multiply Curves by K-Factor

Note: K-factor is a t-Multiplier

Current

Time

delay B

'a'ba b

Fast)(A

curve) damage (fuse curve MT fuse of %75

BCurve*KB )Multiplier(Time

ACurve*KA )Multiplier(Time

'a 'b

Power System Review

Cooper Reclosers K-Factor

•What is K-Factor?

•K-Factors are Time

multiplying factors for various

Reclosing Intervals. K-Factor

shifts the curves up

increasing the time value by

K-Factor for the same current

value.

Table Below -Curtsey of Cooper Power Systems

Power System Review

Source Fuse-Recloser Coordination

Phase Trip Setting Steps:

1. Calculate Full Load Iprim & Isec

2. Select an Appropriate Fuse size

Fuse Size: 1.5x126.3A=189.5A → Select 200K

3. Select an Appropriate Recloser Coil Size:

Calculate Coil Size: 1.25x400=500A

Select Coil size: 560A

4. Desired Minimum Phase Trip= 2.5 x Peak Load to

override the Inrush

AIAIprim 694316.4

5000sec3.126

386.22

5000

E1&1

C2&A2

Recloser

2Ag

RX

%6

5000

Z

KVA

kVkV 16.4/86.22

R

FAULTLineofEnd

FUSE

R

AxIPhase 10004005.2

Note: Cooper W & RX type Recloser Ratings:

Coil Size Min Trip Rating Interrupting Rating

560 A 1120 A 10,000 A

3800AFaultG-

4500AFault-3

AFaultG 175

1500AFault-3

400A(Peak)I

Source Fuse-Recloser Coordination Ground Trip Setting Steps:

1. Estimate Normal Load unbalance: 10% of Peak-Load

Example: Iunbalance= 10% of Peak Load

Iunbalance-Normal= 0.1 x 400=40A

2. Estimate the load unbalance created by the largest

single-phase device:

Example: Assume the largest single phase Load is 90A

Fuse. Iunbalance-Load=90A

3. Calculate Unbalanced downline Ground Current:

4. Select Minimum Ground Trip:

AIGround 1304090 LoadunbalanceNormalunbalanceGround III

)A175()A140()A130( FaultMinSettingGroundUnbalancedG III

A140 TripMinIg

Source Side Fuse-Recloser Coordination

Recloser-Fuse (Load Side) Coordination

•Determine an appropriate Fuse size @ Point B

•Which fuse coordinates the best (100K or 140K?)

•Answer 140K; Why?

CA

RX

22

Recloser

%6

5000

Z

KVA

kVkV 16.4/86.22

R

AFaultMin

A

FAULT

600

1900G

FUSE R

Amp400

Amp90

B

Power System Review

Recloser-Fuse (Load Side) Coordination

AK

AK

2380140

1112100

LimitonCoordinatiFuse

AFaultG 175

1500AFault-3

E1&1

C2&A2

Recloser

2Ag

RX

%6

5000

Z

KVA

kVkV 16.4/86.22

R

FAULTLineofEnd

FUSER

3800AFaultG-

4500AFault-3

AFaultG 175

1500AFault-3

400A(Peak)I

B

Relays

Mechanical

&

Digital

Protection System Elements

Protective relays

Circuit breakers

Current and voltage transducers

Communications channels

DC supply system

Control cables

Three-Phase Diagram of the Protection Team

CTs

VTs

Relay

CB

Control

Protected

Equipment

SI

52

TC

DC Station

Battery SI

Relay

Contact

Relay

Circuit

Breaker

52a

+–

Red

Lamp

Most Common Protective Relays

Protection Principles for Transmission &

Distribution Lines:

Overcurrent (50, 51, 50N, 51N)

Directional Overcurrent (67, 67N)

Distance (21, 21N)

Differential (87)

Circuit Breaker Selection

Relay (The Brain)

CT Ratio

PT or VT Ratio

Interrupting Cycle

Voltage Class

K rating=(VMAX/Vmin)

BIL rating

Power System Review

Load

Ib

Relay-Circuit Breaker Operation

Load

Phase relays

Ground relay

CTs

Circuit

Breaker

In

A

B

C

Ia Ib Ic

Ia

Ib Ic

cban IIII

LOAD

Power System Review

Induction-Type Relays

Power System Review

Relay Classification

Overcurrent

Overvoltage

Undervoltage

Differential

Directional

Under Frequency

Distance

Power System Review

Relays for Phase Faults

Time overcurrent 51

Instantaneous & time overcurrent 50/51

Directional Time Overcurrent 67

Instantaneous & directional time over current

50/67

Directional Instantaneous Overcurrent 67

Step Time Overcurrent 51

Directional Instantaneous and directional 67

Zone Distance 21

Power System Review

Relays for Ground Faults

Time Overcurrent 51N

Instantaneous & Time Overcurrent 50N/51N

Product Overcurrent 67N

Instantaneous and Product Overcurrent 67N/50N

Directional time overcurrent 67N

Instantaneous and directional time overcurrent 67N

Directional Instantaneous Overcurrent 67N

Three-zone distance system 21N

Power System Review

Transformer Protection

Open-Phase Condition

CTs=600/5

In

A

B

C

Ia Ib Ic In

Ia

Ic

can III 0

Open

400 a 0 a 400 a

60333.3

886.2666.1

886.2667.1333.3

120333.3,0,0333.3

120

n

n

n

a

Ratio

I

jIn

jI

IcIaIcIbIaI

IcIbI

CT

Ground Relay Could Pickup

60333.3nI

1203.303.3

0

Single-Phase to Ground

Fault

CTs=600/5

In

A

B

C

Ib Ia

Ic

07.46nI

Short 6,000a

400 a 400 a

0666.46

667.1667.150

120333.3120333.3,050

120

n

n

n

a

Ratio

I

I

IcIbIaI

IcIbI

CT

SCI

050aI 1203.3

1203.3

In

SCI

Ground & Phase Relays both Pickup

Line-to-Line to Ground Fault

CTs=600/5

In

A

B

C

Ib Ia

Ic

607.46nI

Short 6,000a

400 a

6067.46

415.40333.23

886.2667.1301.432550

120333.312050,050

120

n

n

n

a

Ratio

I

jIn

jjI

IcIbIaI

IcIbI

CT

SCI

050aI 1203.3

In

aI

Ground & Phase Relays both Pickup

SCI

12050

bI CI

Three-Phase to Ground

Fault

CTs=600/5

In

A

B

C

Ib Ia

Ic

0nI

Short

0

120100120100,0100

120

n

n

a

Ratio

I

IcIbIaI

IcIbI

CT

SCI

0100aI2100aIb

aIc 100

000,12cI000,12bI000,12aI

000,12aI

SCI SCI000,12aI 000,12aI

Only Phase Relays Pickup Ib

Ia

Ic

Relay Settings

Time Overcurrent pickup

& time setting must be

capable of handling:

Peak Load

Cold-Load Pickup

Motor starting

Instantaneous Setting

must be capable of

handling:

XFMR Inrush

Capacitor Inrush

Asymmetrical Faults Safety factor=1.2xSymm Fault

Two Settings:

1. Time Overcurrent

2. Instantaneous

Power System Review

Relay Settings

Phase Time Over Current (TOC) Setting

Phase pick up:

Method 1: 2xImax < I Pick up < I Min (phase-phase Fault current)

Note: Ensure I Min-Fault ≥ 2 x I Peak- Load

I Min=Iphase-to-Phase=0.866 x I Three-Phase fault

Method 2: 25% Margin ; IPickup= Ifull-load/0.80

Ground Time Over Current (TOC) Setting

Ground Pick up:

Method 1: 2xI Normal ground Current < I Pick up< I Min Ground Fault Current

Where; Normal Ground Current Range: 10% to 20% of Load Current

Method 2: Ipickup=(0.40 to 0.75)x Ipeak-Load

Power System Review

Instantaneous Relays Pickup

Settings

Instantaneous Pickup

Range:

Typical Instantaneous Phase & Ground

Pick up= 2x Time Over Current relay pick ups

PickupPhaseeousinsPickupPhase IxIIx 102 tantan

Power System Review

How to determine Pickup &

Time Dial? Step 1: Calculate Short Circuit Current @ each Bus

( usually Phase-Phase Fault)

Step 2: Identify CT Ratio & Breaker Interrupting Cycles at

each Bus

Step 3: Calculate Relay Minimum Pickup for each Device

Step 3: Starts with the last relay and apply Time Margin of

0.3 to 0.4 sec (ANSI/IEEE Std-242 )between Relays:

o CB’s operating time (5 cycles): 0.08 sec

o Relay Over travel time: 0.1 sec

o Safety factor (CT saturation, Errors): 0.22 sec

Total 0.4 Seconds

Power System Review

0.4 Sec

Relay-Relay Setting

Power System Review

TCC Coordination Time

Margins

Relay-Fuse TCC Curve Separation Rule:

Mechanical Relay requires minimum time margin of 0.3 sec

time interval

Digital Relay requires minimum time margin of 0.2 sec time

interval

Relay-Relay (Mechanical) TCC Curve Separation Rule:

According to ANSI/IEEE Std-242:1986, the rime interval

between two relays in series must be 0.3 to 0.4 seconds.

This time interval components are:

Circuit Breaker Operating Time(5cycle): 0.08 sec

Relay Overtravel Time: 0.1 sec

Safety factor for CT Saturation & errors: 0.22 sec

Power System Review

Relay-Relay (Digital)TCC Curve Separation:

Time margin between series Relays must be minimum of

0.25 sec. This time separation consists of the following:

5 Cycle Breaker (0.08 sec)

Relay Accuracy (0.04 sec)

Safety factor & CT Ration (0.13 sec)

Relay-Recloser

Time Margin between Mechanical Relay & Hydraulic

Recloser must be minimum of 0.28-0.30 sec

Time Margin between Mechanical Relay & Electronic

Recloser must be minimum of 0.25 sec

TCC Coordination

Time Margins

Power System Review

Relay-Recloser-Fuse

Coordination In the following CKT coordinate Breaker B1, Cooper

Form-4C Recloser, ABB PCD2000 Reclsoer, and 100K

Tap Fuse.

1B R 3R

1L 2L 3L

400ALoad

4CForm

Cooper

3 2 1MVA25

kVkV 86.22/115

PCD2000

ABB

A1000

A40003

2@

FaultMin

BusFAULT

K100

AFaultMin

A

BusFAULT

443

30003

1@

A2000NΦ

A60003

3@

BusFAULT

2B

300ALoad 200ALoad

231ALoad

BUS

kV115

Power System Review


Relay settings:

Phase setting: PU=2.4 x 400=960A

Ground setting: PU= 960/2=480 A

Cooper Recloser Form 4C settings:

Phase setting: PU=2x300=600A

Ground setting: 160A<PU=600/3=200A<443A

ABB Recloser Model PCD2000 settings:

Phase setting: PU=2x200=400A

Ground setting: 140A<(PU=150 A)<443

Power System Review

Over Voltage Protection

Insulation Voltage Class

Basic Impulse Level (BIL)

Nameplate Rating

Surge arrestors.

Power System Review

Overvoltage Protection

Sources of Overvoltage:

Ferroresonance

Low Order Hormonics

Voltage Regulation (XFMR LTC Malfunction)

Transients caused by:

Lightning surge

Switching operations

Line-to-Ground faults

Capacitor Bank Switching

Protection methods:

Surge Arresters(ANSI C62.1-1981)

Static Wires

Useful IEEE/ANSI Standards Graph of Curves can be found in ANSI/IEEE Standard

C37.91-1985, “Guide for Protective Relay Applications

to Power Transformers,”

ANSI/IEEE C57.109-1993, “Guide for Transformer

Through-Fault Current Duration.”

IEEE/ANSI Standards 141&242

IEEE Std 242 – Buff Book

IEEE Std 141 – Red Book

IEEE Std 399 – Brown Book

•IEEE C37.90 – Relays

IEEE C37.91 – Transformer Protection

IEEE C37.102 – Guide for AC Generator Protection

References

1. J.D. Golver, M.S. Sarma, Power System Analysis and design,

4th ed., (Thomson Crop, 2008).

2. M.S. Sarma, Electric Machines, 2nd ed., (West Publishing Company,

1985).

3. A.E. Fitzgerald, C. Kingsley, and S. Umans, Electric

Machinery, 4th ed. (New York: McGraw-Hill, 1983).

4. P.M. Anderson, Analysis of Faulted Power systems(Ames, IA: Iowa

Satate university Press, 1973).

5.W.D. Stevenson, Jr., Elements of Power System Analysis, 4th

ed. (New York: McGraw-Hill, 1982).

Solution

Answer: 37.5 KVA

Break Time !!!!!

APPA-Module 7-Protection & Coordination

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