Most Common Errors in Service Entrance and Load Side Installations Prior to Final DU Inspection

7/25/2019 Most Common Errors in Service Entrance and Load Side Installations Prior to Final DU Inspection

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Most Common Errors in

Service Entrance and

Load Side InstallationsPrior to Final DU Inspection

Industrial and Commercial Buildings

Primary Voltage / Overhead

For RME Forum November 28, 2014IIEE Convention

Presented by : Ray Anthony Rodriguez

Team Leader- Meralco South CBG Technical Support


2/193

Format of Presentation:

1. Error Mentioned or Shown2. Relevant Standards or Codes

3. Possible Corrections (-optional)


3/193

Contents :1. What is Primary Metering?

2. RME Responsibilities3. Errors

b. Location of Lightning Arresters

c. Using ABS instead of LBS

d. Not Proper Coordinatione. Not Appropriate Transformer BIL

and Connections


4/193

References :


5/193


6/193

BulacanBulacan

Metro ManilaMetro Manila RizalRizal

PampangaPampanga C

C

D C

A C C

B C C

CB A ( A) C

CB B&C (AC A) C

C E C

F () C

. B

A C

B D C

E C, C , C C

A C

CC C C

F . E C

E C C

C

C C

B

A B

( ) C

C L C

Major Load Growth CentersMajor Load Growth CentersMajor Load Growth CentersMajor Load Growth Centers

CaviteCavite

LagunaLaguna

BatangasBatangas

QuezonQuezon

CaviteCavite

LagunaLaguna

QuezonQuezon

B C

F C E C

C C

D C

F C C

( )

F B

C

H E

B B

C (C )

( ) B

F C C C

C C

L L C

A

L BA L

E C

A

( ) H . E (MEALAND) L

L

E L

A G L

C

C

C


7/193

Generation - Transmission - Distribution

Power Plants Transmission Lines

7

SubstationTransformers &

Equipment

DistributionLines &

Transformers

Customers


8/193

C

/B

&

C

/+ /+ /+ /+


9/193


10/193

M


11/193

, O I,CO

D = 5 30


12/193

M


13/193


14/193

Registered Master Electricians


15/193


16/193


17/193


18/193


Service Entrance and

Prior to Final DU Inspection


19/193

Not Enough Clearance

from other Conductors,Buildin s Structures and

Trees


20/193

Upper Level

Conductors

Open

Secondary

upto 750V

Primary upto

13.8 kV Y or

Delta 34.5Y/20 kV 115 kVLower Level

Conductors/ Nature of

Surface

mm (ft-in) mm (ft-in) mm (ft-in) mm (ft-in)

Railroad Tracks

7500 (24' 7") 8100 (26' 7'') 8100 (26' 7'') 8580 (28' 2")

Vertical Clearance of Wires, conductors or cables above ground, etc,

when it crosses over or overhang the surface

D

,

other areas subject to

truck traffic

5000 (16' 5") 5600 (18' 4") 5600 (18' 4") 6080 (19' 11")

Driveways,parking lots

and alleys

5000 (16' 5") 5600 (18' 4") 5600 (18' 4") 6080 (19' 11")

Spaces and ways

subject to pedestrians

or restricted traffic only

3800 (12' 6") 4400 (14' 5") 4400 (14' 5") 4880 (16')

13.8 kV Y or Delta470 (1' 7") 600 (2') 660 (2' 2") 1160 (3' 10")

34.5Y/20 kV530 (1' 9") 660 (2' 2") 725 (2' 4") 1220 (4')

115 kV 1030 (3' 5") 1160 (3' 10") 1220 (4') 1720 (5' 7")

Vertical Clearance at Supports Between Line Conductors


21/193

Distance from DUPrimary Metering

Pole Is less than 5

meters


22/193

Too Near to DU Pole and Lines


23/193

F6 G C B


24/193

Not Enough Working ClearanceBetween Poles and Insulators


25/193

Too Near to Buildings


26/193

Too Near to DU Primary Lines


27/193

Vertical Clearance Between Supply ConductorsSupported on the Same Structure

For 34.5/ 20 kV lines = 725 mm or 2 4

Clearances Between Wires Conductors or

Cables Carried on Different SupportingStructures

For 34.5/ 20 kV lines onlyHorizontal = 1500 mm

Vertical = 600 mm


28/193

Distance from DU

Primary Metering

Pole Is less than 5

meters


29/193

Working Clearance and distance from building


30/193

Not Enough Working Clearance


31/193

N E C


32/193

E C

& B


33/193

Crisscrossing of DU

and Customers Wiresalso clearances

Sangley Point Navy & Air Force


34/193

Not Enough Clearances

from Buildings


35/193

Not Enough Clearances

from Buildings


36/193

Upper Level

Conductors

Open

Secondary

upto 750V

Primary upto

13.8 kV Y or

Delta 34.5Y/20 kV 115 kVLower Level

Conductors/ Nature of

Surface

mm (ft-in) mm (ft-in) mm (ft-in) mm (ft-in)

Railroad Tracks

7500 (24' 7") 8100 (26' 7'') 8100 (26' 7'') 8580 (28' 2")

Vertical Clearance of Wires, conductors or cables above ground, etc,

when it crosses over or overhang the surface

D

,

other areas subject to

truck traffic

5000 (16' 5") 5600 (18' 4") 5600 (18' 4") 6080 (19' 11")

Driveways,parking lots

and alleys

5000 (16' 5") 5600 (18' 4") 5600 (18' 4") 6080 (19' 11")

Spaces and ways

subject to pedestrians

or restricted traffic only

3800 (12' 6") 4400 (14' 5") 4400 (14' 5") 4880 (16')

13.8 kV Y or Delta470 (1' 7") 600 (2') 660 (2' 2") 1160 (3' 10")

34.5Y/20 kV530 (1' 9") 660 (2' 2") 725 (2' 4") 1220 (4')

115 kV 1030 (3' 5") 1160 (3' 10") 1220 (4') 1720 (5' 7")

Vertical Clearance at Supports Between Line Conductors


37/193


38/193

:

(..

E

,

, .).

F ,

(5)

.

D = M = 5

3C3C


39/193

3C3C

DISTRIBUTORSDISTRIBUTORS


40/193

OLD COSMOSOLD COSMOS SANSAN PEDROPEDRO


41/193

OLD FORDOLD FORD


42/193

SHIN HEUNGSHIN HEUNG

SAMSUNGSAMSUNG


43/193

SAMSUNGSAMSUNG

CPIPCPIP

CALTEXCALTEX


44/193

CALTEXCALTEX

BIANBIAN

CPIP andCPIP and CarmelrayCarmelray 22


45/193

CPIP andCPIP and CarmelrayCarmelray 22


46/193

BOY SCOUTBOY SCOUT

OF THE PHILS, LOS BAOSOF THE PHILS, LOS BAOS

HV SWITCHGEAR BHV SWITCHGEAR B


47/193

HV SWITCHGEAR BHV SWITCHGEAR B

BESIDE METERING POLEBESIDE METERING POLE

PNCC SLEXPNCC SLEX


48/193

PEC Part 2 Table 3.4.6.3 (a) on 115 kV


49/193

PEC Part 2 Table 3.4.6.3 (a) on 115 kV

E l f 115 KV S b t ti


50/193

Example of 115 KV Substations

E ample of 115 KV S bstations


51/193

Example of 115 KV Substations


52/193

LindenLinden STA ROSA 115 KVSTA ROSA 115 KV

YAZAKIYAZAKI


53/193

TORRESTORRES


54/193

ABI,ABI, CabuyaoCabuyao

CPIPCPIP BatinoBatino


55/193

CPIP,CPIP, BatinoBatino


56/193

ALL ABO ABOE 600

EC . 1 1 A 1.10.3.1 1. 10.3.6

CHAE 1. AICLE 1.10 E I

1.10.3 O 600 N 47

1.10.3.2 M D F L 48

1.10.3.5() M D C

E E 52

1.10.3.5() E L A 53


57/193

ALL ABO ABOE 600

EC . 1 1 A 2.25.1.14 2.25.1.26

CHAE 2. AICLE 2.25 O B C F

2.25.3 O 600 132 2.25.3.11 C , ,

, , O L 135

2.25.3.12 C B O 135


58/193

ALL ABO ABOE 600

EC . 1 1 A 3.0.2.1 3.0.2.12

CHAE 3. AICLE 3.0 M

. . ,

3.0.2.20 M C 330

EC . 1 1 A 4.90.2.4

CHAE 4. AICLE 4.9 E O 600

4.90.2.4 M 790 4.90.2.4 M C L 791


59/193

- Distance from distribution lines Article 3.4.5.3 from PEC 2008part 2 pp.140-147 .

- Height wrt to distribution poles Table 3.4.10.5 (b) (1)a p.194 fromPEC 2008 part 2.


60/193

- Distance between conductors orpersonnel Article 3.4

Clearance between wires,conductors or cables at

supports,


61/193

Table 3.4.6.2 (a) (2) a

Horizontal clearance betweenline conductor smaller than

sags.

from PEC 2008 part 2 pp.162-164


62/193

- Clearance from trees Article3.4.5.3 from PEC 2008 part 2

pp.1471 PEC 2009 part1 vol.1


63/193


64/193

Location of Lightning Arresters

Should be located at the Highest Point


65/193

Should be located at the Highest Point

Due to Lightning Strikes


66/193

A

D

Mall STAMall STA ROSAROSA


67/193

Below the

Load Break Switch

Should be above orThe same level

CalambaCalamba IndustrialIndustrial


68/193

Below the

Load Break Switch

Should be above orThe same level

Right Sample


69/193

Lightning Arrester Above all


70/193

Right Sample -Lightning Arrester

Same Height of

LBS


71/193

A

N

() DL

A :

*

MCOM C O

MCO

34.5 27 22 C II

13.8 12 10 C II

13.2 12 10 C II


72/193

- Lightning arrester location Article 2090.3.11 p275-281 fromv .


73/193


74/193

Using Air Break Switches

Instead ofLoad Break Swithces

A B

.


75/193

. A H

.

.

.

A B

. . , ,

. A A B L

.

A B


76/193

Air Break Switch

A

.


77/193

.

D

. A ,

, .

.

A ( F6)

.

.

L B

Load Break Switch


78/193

Load Break Switch


79/193

Load Break Switch


80/193

& :


81/193

LOAD BEAK ICH

, ,

(C O)

. :

N

F

C

C

M

(A)

B

II

L

H A (, .)

13.2 14.4 60 40 95

13.8 14.4 60 40 110

34.5 34.5 60 30 110


82/193


83/193

Not Proper Coordination

Of Protective Devices

: M C I


84/193

Bank 1

83 MVA

Bank 2

83 MVA

Install 2 units of Synchro-check

relay at CIP II Substation for CBs

61SD4/62SD4 and 61SD8/62SD8

: M C I


85/193

SUBSTATION 1

Tap115 kV Line

Bk2

83 MVA

Bk1

83 MVA

SUBSTATION 3Bk350 MVA

SUBSTATION 2

Bank 1

33 MVABank 2

33 MVA

62WW2463WW24Install 2 units of Synchro-check

relay at FPIP Substation for CBs

62WW24/63WW24

61SD4

61SD8

62SD4

62SD8

63XE8

63XE24

Install 1 unit of Synchro-check

relay at Canlubang Substation

for 63XE8/24

SUBSTATION 4

Customers S/S

M

Customers Steam TurbineGenerators

Construction of 4.6 km, 1-795 MCM ACSR

conductor per phase from tapping point at FPIP-

Los Baos 115 kV Line to MGPP Switchyard

Install N.C. 115 kV LineDisconnect Switch and2 units LAs

Bank 1

33 MVA

Bank 2

115 kV-13.8 kV

25 MVA

Bank 1

115 kV-13.8 kV

25 MVA

G2 G1

SUBSTATION 5

63WT4

61WT4

Install 2 units of Synchro-check

relay at Los Baos Substation

for 63WT4/61WT4

64ZX4

Install 1 unit of Synchro-

check relay at Calauan

Substation for 64ZX4

Install 1 unit of 115 kV PT

Install 2 units of 115 kV PTs

Below 115 kV

Legend:230 kV

115 kV

Proposed 115 kV

for MGPP

115 kV SCF & Metering

: M B F D


86/193

Protection Coordination


87/193

Time,sec

10

100

50

5

30E

1,000A 2,000A

1A

34.5

= 16.7A

= 1,000A

3 = 2,000A

M =

30E

16.7 1.6 = 26.72 30E

Current, amp

0.01

0.1

0.5

0.05

10

100

1000

10000

10000 0

50

500

5000

5000 0

Breaker Ground

Delay Curve

Breaker Ground

Inst. Curve

Breaker Phase

Delay Curve

Breaker Phase

Inst. Curve

MMT curve TCT curve

C


88/193

Using Maximum Rating

Instead of proper coordinationWith DU rotection

M F L

O D


89/193

O D

M F L

O D


90/193

O D

C F


91/193


92/193

Power Fuse or

Fuse Cutouts ?

Power Fuses


93/193


94/193

Fuse Cutouts


95/193

F C

F C I I B


96/193

N

F

C

C

I

C

I

B

I

I

L

H A . (, .)

13.2 14.4 60 16 5 95

13.8 14.4 60 16 5 110

34.5 34.5 60 16 5 200


97/193

Power Fuse or Fuse Cutouts ?

C F


98/193


99/193

Multiple Set of

Power Fuses

M F

B F


100/193

B F

/C

J O (1)


101/193

J O (1) F


102/193


103/193

Not Appropriate

Transformer Specificationsand Connections


104/193

C:

,

.

TRANSFORMER CONNECTON(Advantages and Disadvantages)

Case I. Delta Grounded Wye


105/193

Case I. Delta Grounded Wye(Recommended why?)

Advantages:

1. Complete symmetry and currents with respect to the three (3)lines to neutral.

2. It provides two different values of secondary voltage instead of

one; i.e -480/277v. (Less expensive in design compared todelta delta connections in terms of insulation).

3. Stable neutral because of the delta, primary and good current

balance; i.e., overall loading can be closely balanced.

4. Most satisfactory connection due to a wide applications in LVdistribution systems, i.e., commercial buildings of power andlighting service.

Disadvantages:

1. It is also susceptible to ferroresonance *, especially during 1sequential switching when energized in series with cable


106/193

sequential switching when energized in series with cablecapacitance to ground.

2. The bank cannot be parallel with D-D or Y-Y banks because ofthe phase difference of 30 degrees between line voltages ofthe banks on the secondary side.

* F

.

I

( ) ( ). I

, .

I ,

.

3

(3) .

,

,

A. Advantage to Distribution Utility

1. Any unbalancing of load the secondary will just becontained at the primary System neutral current will not


107/193

contained at the primary. System neutral current will notbe affected.

B. Advantage to Wye Grounded Secondary to Customer

1. Smaller fault current.

2. Fault in any leg will be readily isolated. (In delta connectedsecondary, it is necessary to have two legs on before itcan be isolated. If only any one legs on faulty, it isnecessary to wait for a fault on another leg before it canbe isolated.

3. Economy in insulation, since than delta connectedsecondary.


108/193

Case IV. Grounded Wye Delta:

Ad t


109/193

Advantages:

1. Drastically reduces the possibility of ferroresonance.

2. In case of fuse blowing of one line on the primary, 3-phasepower is continued to be served the secondary. It operatesas an open type-open delta bank and a the wye connection

continues to carry the load as much a 58% of a closed.

3. All voltages are balanced and no roving neutrals arepresent.

Disadvantages:

1 Transformer bank acts as grounding transformer for fault


110/193

1. Transformer bank acts as grounding transformer for faultexternal to itself.

2. Unbalanced in load between phases cause current to flowin other wye-delta transformer banks connected to thesame line.

3. If transformer normally carries 100% load, fuse blowing none line on the primary will cause the remaining twophases (open wye - open delta operation) overload by 73%.


111/193

G di B k


112/193

Grounding Bank

Transformer


113/193


114/193

BIL B I L. I

, .

BIL:


115/193

, .

BIL

.

, .

.

I ,

.

,

.

> & C

O E / D


116/193

B

B I I L(, M)

D A . . .

D 95 95 150

, C

95 110 150

110 110 200

D 110 110 200

ANSI- IEEE and IEC on BIL


117/193

?

A 34.5 :

F ANI 100 BIL

A 36 :

F IEC 70 BIL

ANSI- IEEE and IEC on BIL


118/193

?

L E

E (EE)

IEC

ANIIEEE

C .

D ? ( )


119/193

. ( )

.

(400 , 200 , 110 , 66 , 33) 200MA.D .

(11, 6.6 , 3.3 , 440, 230) 200 MA.

A , . A

, .

. H,

.

.

.

I .

.I , C D.( F

L)

I (H), C D (F

L) B D , B G

( D ).


120/193

4. Insulator KV rating Table 3.8.4.1.p.245 from PEC 2008 part 2 ora e . . . p. .


121/193


122/193

LBS Handle

Not Connected to

roun ng a

No Grounding Mat


123/193

Operating handle not grounded


124/193

LB H NO C

G M O G


125/193

G M C LB H


126/193

L

G M C LB H


127/193

LB H

G M

G M C LB H


128/193

G M E

I


129/193

G M E

I


130/193


131/193

- Grounding mat connection and

material Article 2.90.3.20 -. . . . -

2009 vol.


132/193


Service Entrance InstallationsP i t Fi l DU I ti


133/193

Prior to Final DU Inspection

-End of Presentation-

Industrial and Commercial Buildings

Primary Voltage / OverheadFor RME Forum November 28, 2014

IIEE Convention

Presented by : Ray Anthony Rodriguez

Team Leader- Meralco South CBG Technical Support


134/193


135/193

Addendum 1

y u

Standard Clearances

D C


136/193

D C


137/193

Vertical Line Configuration

Horizontal Line Configuration

Pole with Vertical Line andHorizontal Line Configuration

Triangular Line Configuration

The applicants primary distribution

Customer-Owned Facilities


138/193

pp p y

facilities and substation shall comply withthe provisions of the latest edition of the

Philippine Electrical Code regarding

safety and clearance requirements.

Vertical Clearance of Conductors Above

Ground or Other Surfaces


139/193

D C


140/193

SAG = measured vertically from conductor (below itsend points) to the straight line joining its

t/ ti l d f th id i t f

Sag


141/193

support/vertical drop of the mid-point of a span

of conductor below its end supports.

SPAN = horizontal distance between support points

141

Level Span

Vertical Clearance Between Supply Conductors

Supported on the Same Structure

For 34 5/ 20 kV lines = 725 mm or 2 4


142/193

For 34.5/ 20 kV lines = 725 mm or 2 4

Clearances Between Wires Conductors or

Cables Carried on Different Supporting

Structures

For 34.5/ 20 kV lines only

Horizontal = 1500 mmVertical = 600 mm

F


143/193

F

Horizontal and Vertical ClearanceBetween Conductors

F

C

Clearances In Any Direction from Line


144/193

Conductors to Supports and to Verticalor Lateral Conductors, Span or Guy

Wires Attached to the Same Support


145/193


146/193

Clearances of Wires, Conductors,


147/193

Cables and Rigid Energized Parts fromBuildings, Signs, Chimneys, Radio and

TV Antennas, Tanks and Other

Installations Except bridges


148/193


149/193


150/193

PEC Requirements


151/193

151

Outermost face of building

D C


152/193

3,000 mm clearance

boundary

(minimum)

Property

Plant strip/

Side walk

facilities

/ B C.

CLEARANCES FROM BUILDINGS

T LEGEND:

V

VH

T T

D C


153/193

ARE PROHIBITEDCONDUCTORS

REGIONS WHERE

CLEARANCECONTROLLING

V

T

H

V

H

H

VT T

HH

Vertical (Arc)

Vertical

T

V

HorizontalH

/ B C.

T

T TV

T

CLEARANCES FROM OTHER STRUCTURES

D C


154/193

VT H

TV

LEGEND:

REGIONS WHERES I G N77H H

V

H

T

VT

H

H

CONDUCTORS

ARE PROHIBITED

H H

V

H

V T

Vertical (Arc)

H Horizontal

Vertical

T

V

CONTROLLINGCLEARANCE

/ B C.

Minimum Clearance (in Millimeters) of Exposed/Non-insulatedWires, Conductors, Cables, and Unguarded Rigid Energized

Parts Adjacent but Not Attached to Buildings and Other

Installations Except Bridges

D C


155/193

Meralco System Voltage, kV

6.24/3.6, 13.8/7.96, 34.5/20 115Clearance of

Conductors Rigid Parts

Conductors

1. Buildings

a. Horizontal(1) To walls, projections,and guarded windows

2 300 2 000 2 750

(2) To unguarded windows 2 300 2 000 2 750

(3) To balconies and areas

readily accessible topedestrians

2 300 2 000 2 750

b. Vertical(1) Over or under roofs orprojections not readilyaccessible to pedestrians

3 800 3 600 4 250

(2) Over or under balconiesand roofs readily accessible

4 100 4 000 4 550

D C


156/193

and roofs readily accessible

to pedestrians(3) Over roofs accessible tovehicles but not sub ect to

4 100 4 000 4 550

truck traffic(4) Over roofs accessible to

truck traffic

5 600 5 500 6 050

2. Signs, chimneys,billboards, radio andtelevision antennas, tanks,and other installations notclassified as buildings orbridgesa. Horizontal 2 300 2 000 2 750b. Vertical (over or under) 2 450 2 300 2 900

CH < (HB HM)/2

:

HB = Height of the building

above ground


157/193

above ground

HM = Height of the topmost

measured at the same

level of reference as the

building

CH = Horizontal clearance

between the outermost

face of the building and

the nearest part of

Meralco facilities

Horizontal ClearanceBetween Conductors Bounding


158/193

the Climbing Space

For 34.5/ 20 kV lines = 1000 mm

C


159/193

Approach Distance to Energized Parts


160/193

For 34.5/ 20 kV lines only- -

Phase-to-Phase = 770 mm

For Outdoor Substation:

Minimum Required Distance

For 34.5/ 20 kV lines


161/193

Vertical & HorizontalClearance from Buildings = 3048 mm

Center-to-center phase spacing for buses = 915 mm

Center-to-center phase spacing for switching = 1219 mmPhase-to-Ground = 610 mm

Between lines of different voltages = 1067 mm

Source: PEC 2009 Vol. 1 Part 1

Article 1.10.3.1 to 1.10.3.6

A D


162/193


163/193

General Guidelines

Measurement of Clearances and Spacings

Unless otherwise specified, clearances shall be measured from

D E C

E A F


164/193

surface to surface and spacings shall be measured center to

.

For clearance purposes, live metallic hardware electrically

connected to line conductors shall be considered part of the line

conductors shall be considered part of the line conductors.

Metallic bases of surge arresters, cutouts and other similar

devices shall be considered as part of the supporting structure.

General Guidelines

Covered Conductors

Covered conductors (including tree wires) shall be considered as

D E C

E A F


165/193

bare conductors for all clearance requirements

General Guidelines

Reduction in Clearance Requirements

The clearances shown in this guideline may be reduced

D E C

E A F


166/193

particularly in cases where the PEC specifically allows or where

.

All reductions in clearances shall conform to allowable limit set

by PEC.

Specific Guidelines

Horizontal Clearance of Supporting Structure from other Objects

Poles, support arms and equipment attached thereto, and braces

D E C

E A F


167/193

shall have the following clearances from other objects. The

objects concerned.

Specific Guidelines


Along streets, roads and highways

D E C

E A F


168/193

Where there are no curbs, supporting structures should be

,

right-of-way to avoid contact with ordinary vehicles.

Location of overhead utility installations on highways with narrow

right-of-way or on urban streets with closely abutting

improvements are special cases which must be resolved in a

manner consistent with prevailing limitations and conditions (PEC

Part 2 2000, Sect. 3.4.2.1 [b][1]).

Specific Guidelines


From Railroad Tracks

D E C

E A F


169/193

For overhead lines crossing or in parallel with railroad tracks, all

, , ,

and equipment attached thereto that are less than 6700 mm above

track rail shall be located not less than 3600 mm from the said

track rail. At industrial sidings (i.e., short railroad tracks

connected to the main track), a clearance of not less than 2130

mm is permitted (Fig. 3)

Specific Guidelines

Overhead Line Clearance

Vertical Clearance of Conductors above Ground or other Surfaces

D E C

E A F


170/193

The vertical clearances specified for conductors above ground

. . . . . . .

be applied at any point in the span. These clearances shall be

maintained considering the maximum span and highest

temperature that can be attained by the conductors during

operation.


171/193

Add d 2


172/193

Addendum 2

Case II. Grounded Wye Grounded Wye

Provided Transformers are:A. Single-Phase Type )

B. Three (3) Phase Shell Type ) Why?C. Three (3) Phase Five (5) legged Core-Type )

Advantages:

A 1 I id diff l f d l


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A. 1. It provides two different values of secondary voltagesinstead of one. (20 KV-139/278V or 34.5 KV-

2. Availability of single phase (1) circuits with only oneconductor run (1 to N voltage)

3. Economical in terms of insulation.4. Provides path for ground current, sufficient for protective

devices to detect and operate.5. Suited to systems having high line voltages and relatively

low currents.6. Best connection to minimize if not totally illuminate the

occurrence of ferroresonance.

Single phase sequential switching at the fuse disconnects does

not produce a ferroresonant condition since transformer magnetizingreactance are not energized in series with the cable capacitance. Thecable capacitance is merely a load on one phase to neutral and is notin series with the transformer magnetizing reactance.


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7. It makes it possible to ground all three phases symmetrically

phase source, making it almost fool proof.

8. Low KV rating of LAs together with discharge spark overvoltage which is consonant with BIL requirement oftransformer as well as other associated equipment thuseconomy in design of the system is achieved.

Additional four (4) oscillograph studies showed that with sinewave voltages between lines, the line to neutral voltages of the Y-Y

banks about 60% third harmonic component.

9. Three phase Shell Type & 5 legged Core Type

I 3 t f f h ll t 5 l d t


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In a 3 transformer of shell-type or 5-legged core- type,react in the same manner as a (3) - 1 distribution-

neutral connected to system neutral. The recommendedconnection is free from ferroresonant overvoltageconditions.

10. Distribution Utility recommends 5-legged core type and not3-legged core type to avoid problems of tank heating due to

unbalances loading condition, or secondary faults whichcause a primary fuse to open.

Disadvantages:

1. Necessitates tertiary windings to stabilize the neutralpotential in the primary wye and to suppress thirdharmonic currents.

2. Severe induction voltages to telephone lines in case of line to

gro nd fa lt


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ground fault.

. ree- egge core type trans ormer exper ences tan eat ng,specially during unbalanced loading.

Remedy: With the use of five-legged core type transformer,shell type transformers or to provide with a lowresistance lines installed in a 3-legged core type willact as a path for the magnetic flux.

4. Deviation of voltage from the theoretical one duringunbalanced load condition.

NOTES:

a) If the primary neutral is not connected to the source


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a) If the primary neutral is not connected to the source,unbalanced load causes a roving neutral. (Roving neutral not stable neutral)

b) If the neutral wire is connected from the source to the neutralof the primaries, each phase can work independently of theother; any unbalanced in current is then carried by theneutral.


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Case III. Delta Delta Connection

Advantages:

1. No third harmonic current will occur.

2. Failure of one phase can still operate as an open delta.

3 Sh i f l d di t th i d f h h


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3. Sharing of load according to the impedance of he phases.

has a high impedance, therefore, it tends to take a smallershare of the load.

4. Availability of balanced symmetrical voltage and currentswith load or at no load.

5. Tank heating is minimized.

Disadvantages:

1. Higher KV rating of arrester needed thereby increase ininvestment of equipment is necessary.

2. No path for sufficient ground current could be provided

thus preventing protection devices to be applicable


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thus preventing protection devices to be applicable.

. rov es on y a s ng e va ue o secon ary vo age noprovided with neutral)

4. At least two conductors or ones could be made to supplysingle phase loads.

5. Higher cost, more insulation required.


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Case V. Ungrounded Primary Wye and Grounded Wye Secondary

with Delta Tertiary:

1 This set-up eliminates the 3rd harmonic problems and


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1. This set-up eliminates the 3 harmonic problems and.

2. The zero sequence reactance Xo, at the delta, provides the

path for the zero sequence current, it has a very low Xoreactance in its grounded wye in a set-up.

Advantages to Distribution Utility any unbalancing of load at thesecondary will just be contained at the primary systemneutral current will not be affected.

Advantages to customer of Grounded Wye secondary:



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2. Fault in any leg of the secondary will be readily isolated.Does not need to wait for a fault on another leg as in delta

connection.

3. Less insulation than DELTA connected.

Disadvantages:

1. Susceptible to ferroresonance

Advantages: Single Phase

1. Same as wye grounded secondary advantages to

customer


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customer.

3. Tank heating eliminated

4. Lower first cost

Three Phase

1. Must be shell type or 5 legged core type to eliminate tankheating.


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Addendum 3


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Addendum 3u

Primary-Metered Service

M

I


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I

(O)

C F (CF)

, I,CO


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, I,CO


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20 / 34.5

I M

I L L

(3 .../3 C...)

20 / 34.5

I M

I L L

(3 .../3 C...)


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M


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M

20 / 34.5

I M

I L L

(3 .../3 C...)

20 / 34.5

I M

I L L

(3 .../3 C...)


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Most Common Errors in Service Entrance and Load Side Installations Prior to Final DU Inspection

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Transcript of Most Common Errors in Service Entrance and Load Side Installations Prior to Final DU Inspection