get-1008l distribution data book

8/20/2019 GET-1008L Distribution Data Book

1/35lo·n

nOMI

DISTRIBUTION DATA BOOK

A col l

ectio

n of fundamental data pe rtain ing to the elements o f and the

loads on distr ibuti on syste

ms

In working on problems involving distribution

circuits and equipmenl our engineers often lind

il convenient to refer to basic data that have been

compiled from various sources

by

our Power

Distribution Systems Engineering Operation.

Since this material

is

equally useful to distribution

engineers in the electric utility industry we are

printing it under one cover and presenting it as

a Distribution Data Book.

GENER L ELECTRIC

GET l

P n

led

in u


2/35

TABLE

OF CONTENTS

SECTION

PAGE

I

Circuit Characteristics . . . . . . . . . . . . . . . . 5

A. Resistance

and

Reactance

of

Overhead Lines 5

B Resistance and Reactance of Cables. . . . . 5

C

Underground Cables 5

D Aeri al Cables. . . . . . . . . . . . . . . . . 11

E Tran

sformer

Characte ri stics .

11

II Underground

Distr

i

bu t

ion Systems

fo

r

Residential Areas . . . . . . . . . . 13

A Primary System 13

B Secondary System . . . 3

C

Transformers 13

O. Separable Insulated

Connector

~ u

~ 14

1

Modules vailable

14

2

Selection

•

. • . . . 14

II I Transformer Connections • 15

A Transformer Polarity 15

B Single-phase Paralleling . . . . . . . . . . . . . 15

C Small Three-phase Step-down Banks 15

1 Delta-delta Banks

. . . . . . . . . . .

. . 15

2 Wye-delta Banks 16

3. Delta·wye Banks . 16

4 Open-wye Open·del

ta

Banks 16

5 Open-delta Open-delta Banks . 16

6 Wye-wye Banks

. 16

7

Caution

. 16

D

Autot

ransformers .

•

.

16

IV. Sh

or t

-circuit Calculations . 17

A Line Impeda nce . . 17

B Transformer Imp edance . . . 17

C Impedance

of

Lines

wit

h Different

Vol

tages.

. . . . . . . . . . . . . . . . . . . . 17

D. Effect of Offset. . . . . . . . . . . . . . . . . . 17

E Per Unit 18

F. Allowable Short -circuit Currents for

Insulated Cond uctors . 19

1

Temperature Limits 19

2 Conductor Heating. . . . . . . 19

3. Characteristics of Short Circuits 19

4 Application Procedure

20

5 Exa

mples of Data

Use . . . . . . .

. .

20

V. Voltage Calcu l

ations

. 22

A Voltage Drop . 22

B

Tables for Est imating Vo ltage

Drop.

. . . . 22

1 Three·phase Problems . . . . . . .

22

2

Single-phase Problems

. . . . . . . . . .

23

VI. Voltage Regulating Equipment . . . . . . . 26

A Selection of Regulator . 26

1

Type

. . . . . . . . . . . . . . .

26

2 Location and Size . . .

26

3. Choice for Three·phase Circuits 28

SECTION

P GE

B Regulator Control Settings . . . . 28

1

Regulator Bandwidth

28

2 Time Delay . . . . . . . . . . . . . . . . . 30

3

Voltage Level 30

4 Line-drop Compensator Setting

Chart . . . . . . . . . . . . . . . . . . . 30

C Light Flicker. . . . . . . . . . . . . . . . . . . . 31

D. Lamp Operating Voltage. . . . . . . . . . . .

32

E

R

educ

tion

of

Light Flicker by

Banking Secondaries. . . . . . . . . . . . . 32

VII. Application of Shunt Cap

ac

it

ors

. . .

33

A Basic Considerations in Applying

Shunt Capacitors . . 33

1 Released Capacity 33

2 Voltage Rise . . . . . . . . . . . . . 34

3. Reduction

of

Losses . . . . . . . . .

. .

34

4 Protection 36

5

Additional Benefits . . . .

36

VII I Lightning Protec tion

of

Di stribution

Systems 39

A. Primary Dist r

ibution

Systems. . . . . . . . . 39

1

Impulse Withstand

Le

vel to

be Protected 39

2 Selection

of Arrester

. . . . . . . 39

3. Effective Location of Arresters 41

4 Special Applications . . . . . . . . . . . 42

5

Lightning Protection of

UD

Systems . 43

6

Overhead Line Protection

. .

43

B Second ary Distribution Systems. . . . . . . 44

IX

Overcurrent

Protection of Distribution

Systems . . . . . . . . . . . . . . .

46

A Primary Circuits . 46

1 Calculating Short-circuit Currents . . 46

2 Selection of Overcurrenr Protective

Equipment

. .

. . 47

3 Coordination Requirements

. . . . . . 49

B.

Seconda

ry

Circuits.

. . . . . . . . . . . . .

. . 50

X. System Design - Loading Data . 51

A. Estimating L

oad

51

B L

oad Factor

51

C

Coincidence of Diversity Factor . . . . . . . 52

D. Distribution Transformer Size 52

E

Th

ermal Loading of

Un

derground

Cables.. 55

F Design of the Secondary System 55

G Monitor ing Transformer Loading 56

XI. Losses and Economic Data . . . . . . . . . . . . 57

A Line Loss . . . . . . . . . . . . . . . . . . . . . . 57

B.

Tr

ansforme r Losses . . . . . . . 57

C. Evaluation of Energy Losses . . .. .

57

D Increased Revenue from Increased

Voltage . . . . . . . . 59

E Pr

esent Va

lue

of 1.00 59


3/35

T BLES

P

Table 1. Physical and e lectrical characteristics of open

-w

ire distribution line conductors . . . . . . .

Table 2.

DC

resis

tance

and correction factors for

AC

resistance

. .

Table 3. Conductor sizes, insulation th ickness and jacket thickness

Part A. Crosslinked -polyethylene-i nsulated cab le

s .

. . . . . . . . . . . • . . . . . . . • . . . .

Part B. Rubber-insulated

cables.

. . . • . _ . _ .• . • • _ . . . • . . . . .

Part C. Paper -insulated cables .

•

.

. .

. . .

•

_ . _

. .

Ta

bl

e 4.

Approximate

distribu tion

transformer

imped

ances.

. . . . . . . . . . . . . . . . . . • . . . . • . . .

. .

Table 5. Full-load curr

ent

of

transformers in amperes • •

Table

6.

Typical data fo r single-

conductor

concentric neutral cable, crosslinked-

po l

yethylene

-insu la

ted . .

.

Table 7. Typical data for si ngle-phase trip lexed 600.., service cable, crosslinked-

jX)lyethylene-insulated . . . _ . . . . . . . . .

Table 8 . Trans

former

imba lance .

Tab le 9. Circuit breakers, circu it reclosers, dist ri bution expulsion ar resters and fuses

Table 10. Max imum short-circuit temper

at

ures for types of insul

at

ion. . . . •

Table 11. Natu ral si nes , tangents and angl es corresponding to cosine values of 1.

00

to

0.00

. . . . . . . .

. .

Table 12. Voltage drops

of

open -wi re lines in volts per 100,000 ampere feet . • . _ .

Table 13. Voltage drops

of

underground cables in volts per 100,000 ampere feet . . . . . . . . . . . . . . .

. .

Table 14. Function

perfo

rmed by regulators and capacitors . . •

Table 15. l oad bonus regulation .

. .

.

Table 16. Power-

factor

co rrection fa

ctors.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. .

Table 17. Applicat ion guide for

group

-

fu

sing ca

pacitor

banks wit h General Electric universal

ca

ble-

type

and oil cut

out

fuse link ratings N ,

OI L

, K , and

T types

(G

ro tmd ed-wye

and

de lta co nnections; 25-,

50

- and 100-kVar units)

. .

Table 18 . Application guide fo r

group

-fusing

capacitor

banks with General Electr ic universal

cab le-type and oil cutou t fuse link ratings N , O i l , K , and T types

(Floating-wye

con

n

ection;

25-,

50

- and 100-kVar units) _

Table 19. Applicat ion gu ide for

group

-fusing capacitor

banks

wit h General Electric universal

cable-

type

and o l cu tout fuse link

rat

in

gs

N , Oil , K , and T types

(Grounded-wye and delta

connect

ions; 150-,2

00

-, and

300

-kVar un its) .

Table 20. Application guide for group-fu sing capacitor banks with General

El

ec tric universal

ca ble-ty pe and o il

cutout

fu se link r

at

in

gs N , O IL

,

UK ,

and T ty pes

(Float ing-wye connections; 150

-,

20 0-, and 300-kVar units) . . . . . . . . . . . . . . . . . .

. .

Table 21. Bas ic impulse insula

tion

leve ls (B lls) and withstand tests .

Table 22. Arrester ratings

vs

maximum overvoltages . .

Table 23. P

erformance

characte

ri

stics

of

General Electric

distribution

arresters

Table 24.

Di

electri c tests for dry-

type

transformers and dry -

type

sh

unt

reactors _• . . • . _ . . _ . .

Table 25. UD transformer-arreste r protection .

. _• • . . • _ . . _

Table 26. T ime-current curves for HR rec losers

. .

Table 27. Distri

bution

transformer losses .

Table 28. Distribution transformer losses

at othe

r than rated voltages . . .

Table 29. Losses for distribution transformers operating

at other

than rated voltages .

Table 30. Prese

nt

values (Vn) of 1 .

00

in vestments

to

be made in years (n) from now, based

on certain rates

of

interest (i)

. .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. .


4/35

I - CIRCUIT CHARACTERISTICS

A.

Res istance and Reactance

of

Overhead Lines

Resistance depends primarily

on

the

conductor

size and

type

of

conductor

used. Reactance depends not

only

on the

conductor size but also on the equivalent delta spacing be tween

the conductors. Accordingly, Table 1 gives the physical and

electrical characteristics for commonly used overhead conductor

sizes and types of conductors.

The

conductor

reactance may be separated into

two

parts -

the internal reactance

of

the condu

ctor

including the area

around the conductor of one foot radius and the external

reactance

of

the

conductor

beyond the one· foot radius. Hence,

the total reactance X) per

conductor is

equal

to

the sum of the

two parts, or:

X • Xl X

2

in

ohms

per

1000

feet

Xl

;: reactance of conductor at one foot

X

2

= reactance of

conductor

beyond one foot

Table 1 gives the values for

Xl

for the various

conductor

types and sizes. Fig.

1

gives the va lues of

X

2

for various

equivalent spacings between conductors as may be used in

practice.

For ordinary single· phase circuits. the equivalent spacing is

the distance between conductors. For ordinary three-phase

circuits, the equivalent spacing

is

expressed by

the

formula:

~

x

B

x C where A, B and C are the di stances, center·to·

center.

of

the con ductors.

as

follows:

The reactances of three-conductor or triplexed cables may be

obtained by usi ng t he upper scales of thickness of insulation and

jacket in Fig. 3. For cables not in direct contact with each

other, use

the bott

o m scale (abscissa)

of

Fig. 3.

Example showing me

th

o of us ing Tables)

Given: A triplexed

50

0

MCM.

aluminum, 15 kV grounded

neutral , shielded and jacketed cross-l inked polye

th

ylene cable,

9OC.

From Table 2. D-C resistance at 25C

=

0.03538 ohms

per

1000

228

90

feet. At 9OC, the resistance would

be 0.03538

x 253 ..

0.04447 ohms per

1000

feet. The a·c correction factor

is

1.

06,

50 the a·c resistanct at 9OC 0.0447 x 1.06 =

0.04714 ohms

per

1000 feet.

From Table 3, Part A. The insulation thickness

is

175 mils. The

jacket thickness is 80 mi ls. An additional 100 mils shou ld be

added for semicon layers and shielding. (See

pa

ragraph C. w

hi

ch

follows.)

The

total thickness of insulation and sheath system

is

1

75

80 100

355

m

s.

From Fig.

3.

At the

in

tersection of 500

MCM

and

355

mils

(interpole between 350 and 400 mils), read 0.036 ohms per

1000 feet.

Underground Cables

To

assist

in

obtaining the spacings. a few typical arrange. C.

ments wit h their equivalent spacings are shown in F

ig.

2. The

arrangements used in practice wi ll vary from system to system,

For three·conductor cables, the insulation thicknesses

ordinar

ily

used can be obtained from Table 3, Parts A,

Band C,

and then the reactance can be

obta

ined directly from Fi

g.

3 at

the intersection

of

the cable si

ze

and insulation thickness lines.

On th ree-conductor cables an i

dentify

ing

tape is

frequently

applied over the insulation of t

he

individual conductors. Th is

tape

usually adds approximately 30 mils to the diameter of the

ooncluctor and consequently 15 mils snould

be

added to the

insulation thickness to find the correct value of reactance. For

inner semi·con tapes,

outer

semi·co n tapes and shield add 100

mils when this shielding system

is

used. Metallic tape insulation

shields generally add 10 to 30 mils to cable diameter. For sector

cables use a corresponding round

conduc

tor diameter.

but because of space limitat ions only these few are shown.

8.

Re

sistance

an

d Reactance

of

Cables

Cable resistances are given in Table

2,

and cable reactances in

Fig. 3. The reactance data

that

follow are based

on

the formula:

X ..

0.023

(loge K

X

=

Reactance in

ohms

per

1000

feet at 60 hertz.

S • Spacing of conductors (center·to·center) in inches.

D

=

Diameter of conductor in inches.

K - A coefficient dependent on the ratio of the inside

diameter of a con

ductor to

the outside diameter of the

cond uctor. For cable of standard·strand construct ion, K

equals 0 .25.

These reactance curves are co rr

ect

for shielded or non,

shielded cable without a magnetic bin der.

To obtain the reactance for three single condu

cto

r cab les

with random spacing in a conduit , multiply the reactance for

three

co

ndu ctor cable spacing (Fig. 3) by 1.20 for non·magnetic

oond uit or by 1.50 for magnetic conduit.

Reference on cab le ampacities are given

in

Section X under

Thermal Loading of Underground

Cab les

5


5/35

Table 1. Physical and el

ect

ri

ca

l characterist i

cs

of open

-w

ire distribution line conductors

Size

I I

Diamele

L

o..

Aw,

Str ands) MCM

In I n.

1000 Fl .

Copper - Hilrd Drawn

,

111

16.51

0.1285

50

6

111

26.25 0.162

80

4

(3)

41

.7

4

0.254

.

2

(7)

66.37 0.292

205

•

(7)

83.69

0.328

258

1/0

(7)

105.5 0.368

326

2/0

(7)

133.1

0.414

4

11

3/0

(7)

167

.8

0.464

518

4/0

(7)

211.6 0.522

653

19)

250

0.574 772

119)

300

0.629 926

(1 9)

350

0.679

OS

AUSt

ee

l

ACSR

6

6/ 1 26.25

0.198

36.2

4

6/1

41.74 0.250

57.6

2

6/1

66:37

0.316

91.6

1/0

611

105.54 0,398

145.6

2/0 8/1

133. 1

0.447 183.7

3/0 6/1

167.8 0.502 231.6

410

6/1

211.6 0.563

192.1

2617

266.8

0.642 366.8

26/7

336.4

0.721

462.4

26/7

397 .5

0.783

546.4

26/7

477.0 0.858

655.7

26/7

556.5 0.927

765.0

26

/7

795.0

1.108 1093.0

(S l

rlnds)

AU Aluminum - Ha

rd

Drewn

4

(7) 0.232 390

2

(7)

0.292

62.0

1/0

(7)

0.368

98.5

2/0

(7)

0.41 4

124.3

3/0

(7)

0.

46

4

156.7

410

{7) 0.522

197.6

(7) 266.8

0.586

249.1

(191

336.4

0.666

315.7

19)

397.5 0.724

373.0

( 1

9)

477.0

0.793

447.6

(19

1

556 .5

0.856 522.0

37)

795.0

1.

026

N6.0

Copperwetd _ Copper

8A

0.199

74.3

6A

0.230

101.6

4A

0.290

161.5

2A

0.366

256.8

' Conducror af 80 C. 40

C

AMBIENT, emissivity

-0 .

5 for copper. 0.2 forlliuminum.

LOWl r

current

Vlllues correspond to

srill

air.

Higher

current

vlllues corres

pond

ro

air moving

it

two

feel

pilr

second.

o Resisfimce of

conoocror

in ohms/fOOD

f l, 60

hertz. C remp(Jrllture

-X reactance of

conduc

to r out tJ one foot III ohms per 1000 ft. 60 hertz.

Approx. Amp_

Cap ac

i ty

50 80

70 110

110 161

\45

2

0

170 245

200 285

240 335

280 390

330 450

375 510

425 575

475 635

55

85

75 120

110 165

50

225

175

260

210

305

245

355

290

410

340

480

380 535

430

605

480 670

620

850

75

115

105

60

.45 215

170 250

200 290

240

340

280

400

330


6/35

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(QIOVAL[N

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'n

M

M.

io>

0.08

I

300

7

3-conduclor cable

' 00

thickness of Insula ion

0.0

+ shield a sheath In

250

6

mils

200

.-

.0

I

150

.-.>

5.0

100

V

-

>

450

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7/35

CHARACTERISTICS

Table 3. Conductor sizes,

in

sulation thickness and jacket thi ckne

ss

Part

B.

Rubber insulated cables *

Insula

tion

Thickness

Single-conduct or Jacket Th ickn llS

100

Percent 133

Percent

100 Porcent

133

Per

cen

t

Insul ati on Insul ati on

Insul

atio

n

Insulation

Circu it Co

ndu

c

tor Level t

Le

ve

l'

Co

nd uctor

Level t

Con ductor Lavel

age

Size,

(Grounded

(Ungrounded

Size,

IGr

ou

nd

ed

Size,

(

Un

gr

ou

nd

ed

o ·Phase,

A WG or

Neutral

Neu

tr

all

AWGo.

N ....tr aJ)

AWGo

. Neutra l)

s

MCM m

il

s

mm mit s

mm

MCM

mils

mm

MCM

ml S

I

mm

0·600 1

8·16

30 0.76 30

0.76 18·16 .. .

.. .

.

..

.. .

1

4-9

45 1.14 45 1.14

14

·9

15 0.38 15

0.38

8·2

60

1.52

60 1.52 8·2 30

0.76 30 0.76

1-4/0

80 2.03 80 2.03

1-4/0

45 1.14 45

1.14

225·500

95 2 .41 95

2.4 1 225·500

65 1.65

65 1.

65

525· 1

000 110

2.79

110 2.79

500·1000

65 1.65

65

1.65

Over-IOOD

125 3.18 125

3.18

Over.1

0ClO

95

2041

95

2.41

14

·8

60 1.52 60

1.52

7·2

80 2.03 80

2.03

1


8/35

Table 5. Fu ll-load currents o f transforme

rs

in am peres

Single-ph. sl Circu lls

Circ uil ~ t O

'VA

1

20

24

0 480

2400 4160

4800

7200 762

0 12,000

5

41.7

20.8

I DA

2.08

1.20

1.04

0.69

0.66

0.42

10 83 .3

41.7 20.8 4.17

2.40

2.08

1.39

1.31

0.83

15

125

62.5 31.3 6.25

3.61 3.13

2.08

1.97

1.25

25 208 104

52.1

ID

6.01

5.21

3.48 3,28 208

37,5

3 3

156

78. 1 15.6 9.01

7.8 1 5.21 4.92 3.12

50

417

208

104

20.8

12.0 10.4

6.94

6.56

4.17

75 625 313 156

31.3

18.0

15.6 10.4

9.84

6.25

1

00

833

417

208

41.7 24.0 20.8

13.9

13. 1

8.33

167

1392

696 348

69,6 40.2

34.8 23.2 21.9 13.9

250

2083 1042 521

104 60.1 52.1

34.7

32.8

20,8

333 2775

1388 694 139 SO.O

69.4 46.3

43.7 27.8

500

4167

2083 1

0


9/35

DISTRIBUTION SYSTEMS FOR RESIDENTIAL AREAS

Table 7. Ty

pi

cal dat a for single-phase triplexed 600V service cable, crosslinked polyethy lene

in

sulated

Overall

I

mpeda

n

ce -

Ohm s

Size_AWG Cable

per Condu ctor

% Volt age

Reg ul

ation

or MCM Diamel&r

per

1000

h .

p r 10,000 a mp.h .

Ampa


10/35

Wy

e-delta Banks

I

t

the high-voltage neutral of the transformer bank is

to the

circuit

neutral, the transformer bank may burn

theJoliowing

reasons:

1. It will cafry circulating current in the delta in an attempt

to

balance any unbalanced load connected

to

the primary

line beyond it.

2. It will

act as a grounding bank and

will

supply

fault

current to any fault on the circui l

to

Which

it is

connected.

3. It provides a delta in which triple harmonic currents will

circulate.

All of these effects cause the bank

to

carry current in

to its normal load current, and often this combination

sufficient to cause roast-out of the bank.

When this transformer connection is used, and the high .

neutral of the transformer is not connected to the

neutral,

an

open conductor in the primary results in a

phase input

and

output

of the bank.

If

the transformer

motor

load, a harmful overcurrent

is

produced

in

each

motor circuit. An equal current flows in two

nductors of the motor branch circuit. and the

sum

of the two

flow in the

third

conductor.

The usual overload protection in

motor

circuits consists of a

device in only two

of

the conductors.

If

the highest

the three currents happens to be in the unprotected circuit,

will very likely occur.

If a th ird overload device is installed in each motor circui t.

t

he

likelihood

of

motor failure from this

cause is

is

he probability of an open primary line to the

Such a probability is effected by the kind of

and protective arrangements used in that part of the

Dclta -wye Banks

T

he

comments about

motor

pro tcction in regard to wye·

.

Open·wye, Open-delt a Banks

Distribution lines in rural

areas

often consist of two phase

and one neutral wire. In urban distribution it

is

sometimes

rable

to have multi

·phase, where only single-phase primary

is

b

le

and the second

phase

wire

is

installed. These lines

nate from three-

phase.

four·wire, ground·neutral systems

are known commonly as V' ·phase lines. T

he

major

of

the load laken

from

these

V ·phase

lines

is

but

occasionally it

is

necessary to supply three·

motor

loads from

these

lines. in addi tion

to

a single·phase,

/240·volt connection.

Since both transformers carry the three·phase load, and one

the single·phase load in addition, the latter transformer

be

the larger unit. It must carry the vectorial sum

of

the

of the three·phase load, while

e smaller transformer must carry

only

58 percent

of

the

For example, i f i t is desired to carry a

·phase load of seven kVA and a three.phase load of f ive

kVA.

where the loads have the

same power factor

transformer

sizes are arrived at as follows:

La rge

Smll il

Transformer Trans

fo:mer

Singl

e·

phase 1000

7 kV A

Three-phase load

(0.58 )

51

2.9

2.9

9.9

kVA

2.9

kVA

Required transf

ormer

size

lQkVA

3 kVA

These sizes are based on the assumption that the loads are

continuous, steady·state loads. In actual practice. this is seldom

the

case.

Some judgment can

be

exercised, depending upon the

knowledge of actual load conditions. as in the selection of

transformers for any other application.

5. Open-delta , O

pe

n·de

lt

a

Ba

nks

This connection is similar to open·wye, open·delta except

that the transformers are connected phase·to·phase instead

of

phase·lo·neutral. Selection

of

large and small transformer ratings

can

be made the same way.

6. Wye·wye Banks

A bank of wye·wye transformers should

not

be used unless

the system is four·wi

re.

It is important to remember that the

primary neutral of the transformer bank should be tied

firmly

to the system neutral.

If

this

is not

done, excessi

ve

voltages may

develop on the secondary side.

7. Caution

Single·phase, self·protected transformers should Jot be used

to supply three·phase, four·wire, closed·del ta circuits serving

combined three·phase power and single'phase lighting loads.

If

the secondary breaker in the lighting phase opens, the lighting

phase is

still supplied with 240 volts. With the breaker open,

however, there is nothing to hold the low·voltage neutral at the

midpoint between the 240 volts. The voltage betweef) each

phase

to

ne

u tral will depend on the relative impedance of the

loads connected

on

either side

of

the 120/240·vol t circuit. Since

lhese

are

rarely equal. the lam

ps

on one

side

will probably burn

out from overvoltage.

D. Autotransformers

A considerable saving in cost may often

be

effected by using

autotransformers instead of

two

·winding transformers.

When

it

is

desired to effect a comparatively small voltage change. or

where both voltages are

low

, an autotransformer can usually be

used as successfully as a two·winding transformer.

Autotransformers should not. except under special con·

ditions.

be used

where the difference between the high ·vol

tage

and low

-voltage ratings

is

great.

because

the occurrence

of

g ounds at certain points w ill sllbject the insulation on the

low·voltage circuit to the same stress as the high-voltage circuit.

Auto transformers are rated on the

basis

of their kVA output

rather than the transformer kV A . Efficiencies. regulation and

other electrical characteristics are also

based

on output rating.

IV

- SHO RT-CIRCUIT CALCULATIONS

A. Line Impedance

When the resistance AL and the reactance

XL

have been

determined, the impedance, ZL' of a circuit

can

be obtained

from the relation ZL .. JAL 2 + XL 2.11 limited only

by

a circuit

impedance, the short·circuit current is as follows:

Three ·phase fault = m p r s in each phase.

v3 Z

L

line-Io.neutral fault : -,;=,E--_ amperes, assuming that the

v32ZL

impedance of the phase conductor and the neutral conductor

are

equal and that the phase conductors are arranged like the

points of

an

equilateral triangle with the neutral conductor

an

equal distan

ce

from all

phase

conductors.

l ine

· o· ine fault = am

peres

L

wher

e:

E

=

line·to·line voltage

Zl '

line to neutral impedance in ohms. or the impedance

of

one conductor to the point of fault.

B. Transformer Impedance

It is frequently necessary to take

into

account the effect of

step

·up or step·down transformer banks. The impedance

of

delta·wye, wye·delta. and delta·delta transformer banks should

be

combined directly

with

conductor impedances in calculating

short·circuit currents. The transformer impedance, which is

usually given in percent, will have to be converted to ohms

before it

is

combined wi th the line impedance. This can

be

done

with the relation:

n

10E2

Z - _ '' ' '_

lI - kVA

where:

ZT n ' transformer impedance in ohms

ZT% • transformer impedance in percent

E - line·to·line voltage in kV

kVA = rating of the three· phase transformer bank

The short·circuit currents

for

the combination of line and

transformer

are:

Three·phase fault Vi E amperes in each

phase.

3(Zl

+

ZTn'

Line·to·neutral fault

= ..Jj(

E amperes wi th the

3(2Z

L

+ ZTn'

same assumptions as given under line impedance.

Line·to·line fault ' 2 (Zl .; ZTn amperes.

-In

the case of a multi·grounded

neutral system the

impedance of

the

neutral is

somewhat

less

thao that

of a phase

conductor

of equat

s i ~ e 10

f

igu

ring the impedance of a multi·

grounded

oeutr&1 conduc

tor

, a faCIOr

of 2 3 is sugge ted. because of

the

multiple

path

for

the return

current.

C. Impedance of lines with Different Voltag

When it is necessary to c ombine a line and

impedance with the impedances of another line

of

voltage, the impedance

of

the new line must be

put

o

voltage base as the or iginal line. This

can

be done by

the impedance of the new line

by

the ratio of the sq

line·to ·line voltages of the transformer connectin

together. It must

be

remembered that the ohms

var

ies directly as the voltage squared. Therefore, in

g

l

ow

voltage

to

a higher vottage, the impedance

will

in

vice·versa. The transformer line·to·Hne voltages sq

must

be

taken so that this will be the case.

D. Effect of Offs

et

The magnit ude of the short·circuit current, as

from voltage and impedance values, does not

represent the rms value of the current

for

the first

because of

the fact that the current wave may b

unsymmet r ical

with

respect to its zero axis. The rm

the first half-cycle increases

as

the amount

of

offse

For constant reactance circuits the maximum value

rms

of

the offset current wave

can

attain

with

respec

of the symmetrical current wave is a funct ion. a

things, of the reactance / resistance ratio of the circu

point

of

fault .

tn the Transactions

of

the American Institute

o

Engineers (Vol. 67, 1948) paper entitled

Simplifie

rion of Fault Currents are the various multiplying

be used

with

the currents calculated by the form

These

are t

he basis

of the values shown in Table 9.

When applying circuit breakers, circuit reclosers,

expulsion arresters and fuses. the formulae for the t

which

will

give the highest value

of

rms symmetr

should be used. Then the multiplying factor in Tab

be

applied to determine the rms current which

compared with the rating of the device.

The relationship shown by the curve in Fig. 7

give

that

can be used

in calculating the maximum rms

first half-cycle of fault current. This curve can be u

of Table 9 for checking the suitability of the interrU

of fuse cutouts and reclosers when the circuit con

particular installation

are kno

wn.

Ratio of for Sl,lbstation tr llnsformer plus primary ci

R

exceeds

4 and ts

usually 1

to

3.

Fig. 7. Mult iplying factot

for

det&rmining short ·circ uit

rlll ·ampete·rated devices, such as distribu tion cuto ut

cal

cu

l

8ted Vmm

otrical sho

rt

·c;rcuit

cu

rre

nt


11/35

Table 9. Circuit breaker

s,

circuit reclosers. distribution expulsion a

rr

esters and fuses

Reacun


12/35

CALCULATIONS

•

220

'&D

..,

•

COPP R CONDUCTORS

LU

MINUM CONDUCTORS

': fN _ __ r

i

1

Y ' l ' f I Y f : l J

} t · ~ f

.-

..

.. .

••

,-

. n .. ;

,;;;;

•

•

: ' 1

•

I·

.

-

1-

'"

-

-1000

,..., _no

-'

.

•

Rr ....

N t y e e .. ..

,

, .

..

. . . .

Ou. .

.. c ~ [ O '>

[ . ,.,

..

,.

,

- - t t t t - t - t - i . O ~ H

' e (. ·'

.. 00.

,

.....

,.

t .

0 . ,0 >0. ·7>.·

100 ]0

, CTeL[ .. .

.CTC , EHU • •

:

---{

-{,

, ,.>i-.d -o,;,.,-,,

O,

.

t, . ;('

lIO 10 ,>0 • >0 0.00

•

_I -r- _ 40

,000

'0

.,0

c . . . . $I owe 00 .. e .

' >0''''

111

,,.

Fig. 8. Maximum siZes of insulated copper and alum inum conductors for a conductor t emperature change from 75 C initi

al

to 200 C final during a short·circuit·cu rrent interrupting interval .

A'

.

•

..

:Yf

.

;,:-'

1

..

~

/$

){ .;p

-

-

4. Application

Proce du

re

Step'

- Evaluate the symmetrical short·circuit current

Step 2 - Knowing

th

e clearing time

of

the protective device,

determine a correction fac tor Ko from Fig.

1' .

Mult ply the symmetrical current by factor Ko to

allow for the d·c component

Step 3 - If the problem involves

an

initial temperature other

than 75 C

or

a maximum short·circuit temperature

other th

an

200 C a correction

fa

ctor K

t

should

be

obtained

from

Fig. 9. Multiply the symmetrical

curre

nt

(or its corrected value from Step 2) by the

factor K

t

to allow

for

different limiting temperatures

..

,10

'

.

.

Step 4 - Check the conductor

size

being considered on Fig.

Fig. 9. Corret:tion factors K

t

for initial and ma •.

short

·circuit

temperatu

res

.

,

,

,

'OTo

.

,u..

.'

,

,

,

, ,

, ,

10. Oscillograms showing dec ay of d ·c com ponent

asymmetry of current

and effect

01

S using the corrected value

of

current. The

permissible time should exceed the protector inter·

rupting time to

prevent

cab

le damage.

5. Examples o f Data Use

EHampl a 1 - Feeder ci rcuits are

to

be

run

fr

om

a 48D-volt, 6D-hertz load

center unit su

bst

ation. During

normal

operat ion it has been

decid

ed that a No. 2 AWG

Versato

l Geoprene Cable

(co pper conductor) will provide adequate current·carr ying

capacity. Evautalion indicates

that

the symmetrical shon·

ci.cuit

current

is

16,000

amperes.

The interrup

t ing

time

of

th

e c ho

sen

breaker

is

1.5

cycles

and it is desired to check

the cab le 's short·circuit capacity.

Sol

ution;

Symmetrical curre nt - 16,000

amps.

Time duration - 1.5 cyc les.

Factor Ko - 1.3 (

From

Fig. 111.

Corrected current - 16.00 0 x 1.3 - 20,800 amps.

In

Fig. 8

we

deTermine

thaI

a N

o.2

AWG

copper conductor will

wi

thstand 20,800

amperes for more

than

two cycles. The refore, an

interrupting time o f 1-

1/2

cycles

will

adequately prolect Ihe

cable.

E>


13/35

v - VOLTAGE CALCULATIONS

Voltage Drop

When

the

electrical characteristics of

the

line under con·

have

been

determined, the line

drop for

a

g i ~ n

of power-factor cos can be computed from

formula :

Volts

drop

= I fR

cos J +

X sin 0

here R and X are

the

total resistance and reactance,

of one

conductor

of the line under consideration.

formula

gives the voltage drop on one conductor, line-to

The three-phase line-te-line drop is..j3 imes the above

drop is tw ice the above value, To

drop in percen t, the fo l lowing equation

can

be

%

volts

drop = kVA

fR cosO + X sinO)

10

kV2

kVA

is three·phase kVA, R and X are the

total

resistance

of one

conductor

in ohms and

kV

is

·line kilovolts.

For

single'phase circuits,

kVA is

single·

kVA, R

and X are

total

values

for both

conductors, and

is

the

actual single'phase

kilovolts.

It

can

be seen from

the vector diagram

in

Fig. 12

that both

are approximate, but are close enough

for

practica l

In this diagram, is shown

as

the

powedactor

angle at the

of

the feeder because,

on

most

distribution

feeders,

is

the

only lo

cation at

which

the power factor

of

the load

be

measured.

To assist in the application of this formula, Table 11 has

le gives

the

values of ,sines, tangents, and

l

es

which correspond

to

cosine or power·factor values

from

O.

In actual practice, loads are usually distributed over the

rather than concentrated at one end. When this is the

simpl ifying assumptions can often be made. These are

own in

Fig. 1

3.

For instance,

if

a load

is uniformly distributed

the

drop to

the end

of

the tine

is

the

same as if

to t

al

load were concentrated at a

point

half

way out

on the

. Th is is mathematically correct

for

a very large number of

For a small number of

distributed

loads the error may be

When the load can be divided into a number of large

loads

distributed

along the tines,

it is

possible to

lin

e

into

the sections between loads

for

calculation

to

consider each section

individually

w

ith

the

hich

it

carries.

If there is

distributed

load

on

a line and it is desired to

find

voltage

drop to

some

point on

the line, the

following

will be

helpful:

kVA

(R

cosO+X sinO)

Ll

% volts drop = 2

10

kV

e re:

kVA

"

total

three·phase load

in

L l ine

A • resistance per 1000

It

X '" reactance per 1000

It

'

source power' factor angle

L l • distance

from

source

to

desired

point

in

thousands of feet

L . total length of line in thousands of feet

CoI(ula led d,ap

Fig.

12. VlI(:

lor diagrem

~ ~ = = : : = = = = = = = O ~ ~ r ~ ~ = = ~ ~ ; :

v,

,.

B. T

ab

les for Estimating Voltage Drop

Voltage drops

for

open·wire and cable circuits can be

quickly

estimated by simple calc

ul

ations and

use of

the foflowing

ampe

re · eet tables. The values given in the tables are the

absolute difference in voltage (voltage drop) between sending

end and receiving end line·

to

·neutral voltages

of

a balanced

three·phase

circuit for

each 100,000 ampere·feet of combined

load and circu

it

length. Tab le 12 covers standard. open·wire

three·phase voltages used for distribution. A wide range of

spacing is use d to cover various line construction. Table

13

gives

similar

information for

various

classes of distribution

cable

voltages.

1. Th ree ·phase Prob lems

In using

the

tables. the

first

thing required is

the

number of

ampere·feet involved

in

the problem. This

is

obtained

by

multiplying

the amperes per phase by length

of circuit in feet.

Divide this ampere·feet by 100

,000

to determine the multiplier

to be used

wit

h values in the tables. For the

proper

voltage,

conductor s ze,

conductor

material, power factor, and

conductor spacing (interpolate, if necessary) find the vol tage

drop factor in

the table and mul t

iply by

the

multiplier

determined previously. Th is

will

be the absolute line·to·neutral

volts

differe

nce (drop) between the sending and receiving ends

of the

circuit.

Dividing

by

l ine·to·:1eutral voltage

of

sending end

So . e. LlRt

(A)

tatle

t

M,a

l

t


14/35

Tabl

e 12.

Voltage drops of open_wire

lin

es

in yolts

per 100

,

000 ampere le et Inote

1)

SYSTEM VOLTAGE CLASS

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Table 13. Vo ltage drops

of underground

cab l

es

in volts per 100 ,000

ampere

feel see note

CABLE VOLTAGE CLASS 000 V

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18/35

VI

- VOLTAGE REGULATING EQUIPMENT

. Selection of Regulator

The

two

fundamental factors

of

service, from both the

r's and the operating company's point-of-view,

is

the

of continuity and as nearly a constant vol tage

as

is

economically possible. To the consumer,

an

in

voltage regulation means greater satisfaction

electric devices and a stronger incentive

for

extending the

of electric energy. To the operating company, an improve·

in voltage regulation results in greater customer satisfac

greater goodw ill towards the operating company, an

of service rendered, and a higher

average

vol

tage

ich results in higher revenue to the company for the

va lue of connected load. Where the load

is

chiefly lighting

as in residential areas, this variation

in kW

·hr

will

be most pronounced .

Fig.

14 gives the

on typical circuits.

. Type

Several different types of equipment are used to maintain

roughout a system. This equipment can be

into three major classes:

1.

Source voltage control; generat ing station bus voltage

control.

2. Voltage ratio control.

a. l oad tap changing transformers

b. Step voltage regulators

c. Induct ion voltage regulators

3.

Ki

lovar control

a. Synchronous condensers

b. Switched capaci tors

The l ypes and sizes of the equipment chosen depend upon

of the load and the characteristics of the system.

It

should be recognized that

the

easiest and least expensive

et hod of system voltage control

is

by variation of the

X

>14

L

·

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e

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AS5umpliOM

Feeder load loc

i

or

• 0.30,

pI

=0.95

UQhlillQ

l

ood

5 ° 1

10 10 1.

VolloQe

drop ofteelillQ all lighlinQ

lood

7 °1

0 1

drop

01

o

ron uat

p ak

R ...e

llu

. fro m incr o s d

loo

d 0 1

3 c

p.r

kWh

200

,

generating station bus voltage, using the generator field control.

Although fun use shou ld be made of th

is

method of voltage

control, this met hod alone does not meet all of the require

ments of the system. To meet the system requiremen ts most

utilities use,

in

varying degrees, a combination of

au

tomatic

voltage·ratio and kilovar control or. as applied here, regulators

and shunt capacitors. The question arises as to how much

emphasis should be placed upon each of these methods of

voltage control. The technical functions that can be performed

by regulators and capacitors are given in Table 14.

2. l ocation and Size

To determine the correct location and size of the regulator,

the loading and voltage characterist ics of the circuit should be

known. Also, the voltage conditions from the substation to the

end of the feeder should be known fo r b oth the peak and light

loads. These voltages may be measured or t hey may be

calculated if the following are available: a circuit diagram which

shows

the

size, spacing, and length of conductor;

an

indication

of at least the most important loads and the phases to which

they connect; and a notation

as

to whether the loads and

circuits are single-phase or three·phase.

The size of the regulator depends upon the load which it

must carry and the percent of voltage regulation. Therefore it

is

necessary first to determine the proper location for the

regulator. In determining the location for a regulator it

is

adv isable to consider

the

effect of load growth as well as present

loa

d condit

ions_

If a voltage profile based on a reasonable

estimate of

fu

ture load

is

made and compared with a vo ltage

profile based on present load, a determi nati on of the extent of

voltage control requ ired with time can be made. A regulator

that is sized and located in accordance with this procedure

will

provide proper voltage correct ion for present and future load

conditions. See Fig. 15.

. , ~

00 XlO

2000

XlO

Example: Compensating for a 5-percenr drop at yearly peak load

o

600 kVA increases the annual revenuB $f 250.

Fi

g.

14. Dollar< reve

nu

e

pe

r yea r r ecovered b y

compe

nsating

fo

r vo lt age

dr op a t yea

rly

peak

t

oa

d

VOLT GE REGUL TING E

Table 14. Function pe rformed by re gulators and ca pa citors

P

trlo

rmed By Perfor

...

d By

FI,nc.

ti

on

Voltage Ra To Con

ol Kilo"a. Cont rol

Commllnts

Vo ltage Reg

ul

aTOf

$)

)Switched Capaci to.s

L

c.,

raise and lower OUTPUT VOLTAGE. YES YES '

·

No

inherent

with switched capacit

Or<

bu

this eHect by being swllched off ,

,

Carl rilise

SVSlem

voltages on source or i

"put

NO

YES

side of regulati"g mea"s .

,

Capable

.

stepless

"

small voltage step

YES

NO'

·

Not inherent with switched capaCitors.

bu

control.

duce

small c h

ar>ge5

in vollage if

ba"k

s i ~ e

system

impeda...::e to ba"k is small.

4.

Capable

.

mai"tai"i"g a

±

314-volt band·

YES

NO'

Switched capacilOfs do not usuallv pefmit

w.dth,

bandwidth,

5.

Capable

of

many SWitching operations with· YES

NO'

·

Capacitor switch contacts deterio'Dle

ra

oul

l'eQuent inspec tion.

large numbe,

01

switching operatio"s per da

6.

Reduces 12R loss lI"d 1

2

X loss in system . NO'

YES

·

Not

inherent with uoltage regulators but s

tion in losses may rasult on output side b

,"creased volta{le.

7.

Reduces thermal loading. NO

YES

8. Raises

system

loading capabililV.

YES'

YES

·

Voltage

regulat

ors

will raise

the

loading

ca

output

side

but

will

0"'

raise loading ca

system

on

input side.

NOTE : Neilhe, egulerors nor cepacitofs by themselves can fulf il l all

of

these desired funct,ons. However, used

s a

c ~ m b , a l , o n , ,the twO

voltage

control

can

maintain

relati vely

flat

feeder voltage

profile and

at the same

time

reduce system

lones and provide for

com,derable s

grOWlh on the feeder.

The amount of kVA of regulation required for a single·phase

regu lator

in

a single'phase circuit can be determined as the

product of percent vol tage regulation and the total circuit kVA

beyond the regulator div id ed by 100

(see

Fig. 16.).

A three-phase circuit can be regulated by one th ree-phase

regu

lator, two single-phase regulators, or three single·phase

regu lators. Fig. 17, 18, 19, 20a and 20b show the connections

fo

r the different methods. There are two types of th ree·phase

regulato rs:

a. Three·phase core·and·coi l construction with three·pha

se

switchi

ng

mechanism.

b. Triplex. Three separate single·phase units mechanically

coupled within one rank.

The amount of kVA of regulation required for wye·

connected three-phase regulators

is

equal to the product of

percent voltagE regulation and the circuit kVA beyond the

regulator divided by 100 (see Fig. 17.).

•

;;

>

UI II

moll

~ 0 I t a 9

profll.

- --- - -,;.

Conte

t locollon lOt

tl9uloto. ,IUd In

oeco,donet

. I th

ultimol.

lOad

10 co t

p


19/35

TAGE REGULATING EQUIPMENT

("""'''''

eon

... lon

~ ' £

VA,o

l R

. . . . .

_

) ( I C ~ . u k V ' 1

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..•.

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.:

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Method I

p 11"9>100< in

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VOLTAGE REGULATING E

•

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20/35

REGULATING EQUIPMENT

Singl '

EI,valor

M ~

Hoists

Rleiprotall

ng

Cron

Pumpi

.

,

Compr,,,or.

,

Automalic

;

Spal_wlld .

,

1\

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,'''0'

1

olid Lines

composi

te curves

of

voltage f(icker

studies by

General Electric

Company.

Gener; 1

Electric Rev iew

August

1925;

Kansas City

Power

&

Light

Company, Electrical World

May 19,

1934;

T.

& D. CommiHee, EEl, October 24,1934,

Chicago;

Detroit

Edison

Company;

est

Pennsylvania Power

Company; Public

Service

Company of Northern

Illinois.

DOlled Lines voltage flicker

allowed by two

utilities, references Electrical

World November

3,

1958 and

June

26,

1961.

Fig. 24. Relations of voltage fluc

tuat

ions to frequency of their

occur

rence iincandescent lamps)

consumption corresponding

to

a given connected load.

amount

of

increased revenue resulting

from

the additional

can

be calculated using the

following

formula:

'"

Voltage·sensitive kW·hr Load

Total kW-hl'

load

voltage reduction in band width x load factor x annual peak

x rate in cents per kW-hr.

01 bandwidth

of

one

or two

volts. A change in revenue

from

large voltage changes can be determined by

Fig. 14.

time

delay should

be set

so that a proper compromise

the number

01 tap change operations and the

control

desired. I the

time

delay is

too

short, the

will operate excessively

by

responding to

voltage changes. It is recommended, then , that the

of

operations

be

controlled

by

changing the

time

delay,

than

by

varying the bandwidth.

regulators are cascaded on a

circuit

the regulator

to the source should have the shortest

time

delay setting,

time delays should be increased for regulators. located

is set lor the

from the source.

3. Volt


21/35

Burning lamps

may

be extinguished if voltage drop to appro>:;·

75 percent o the ,ated

ine

voltage.

Fig. 27. FllIores


22/35

OF SHUNT CAPACITORS

p., wnll (a pocUot kVA • .Y

kVA ,

mple: Assume

II 5Q()(}--k

VA SUbstatiorr has II load power faeror

of

0.70

that 2000

k

VA

of

,,pacitors IIf. applied.

The Pf/f·uni t

capacitof

k VA

- 0.40

for which

the

feleased

capaci

tv IH 0.70 power

f lewr

per unit or

(0.24

x

50001 - 1200 kVA. Also

it may be

noted

rhe

dotted

ines) {niH

the

final power faclo

r is IIbOUI 0.92.

Fig.

32.

Thermal ca pacity re lEtlsed bV application0 1 ca pa


23/35

OF SHUNT CAPACITOR

S

ble 17.

App licat ion guide for group-fusi ng capacitor banks with Genera l Electric uni

ve

r

sa

l cab

le-

type and oil

cu tout fuse link rati ngs N, O

IL

, K, and T types

·WVE ANO DELTA CONNECTIONS

BANKS

W

ITH l00

·

KVAR

UNITS

.

. V O I I $

.

4160 Valli 4800

Voln 7200 Vol

.

12470 Vo u.

13200 Volt. 13800 voru

l(u.. N/D,I - '(' T NID,I

."

NIDi Kn"

N/D,I

Kn"

W O r

Kn"

NIOli

Kn"

NID il

."

' ,00

100

/-

50

57/60

50

,.

25 25

25

25

00

-

1

00

/-

-

tOO / -

8s/ tOO

50

.

50

,.

30

-

100

1-

50

50

50

9

51 100

80/ - 851100

85

/ 100

I

-

100/

-

-

100/-

'

100

/-

-

'00 1

-

'00 1

-

'00 1

,

TOR SANKS

WI

TH 25 ANO

50

KVAR

UNITSI

2400

Vol

41

60 Volts

4800

Volls 7200 12410 Yolts

13200

Volts 13800 VoU,

e

1(

3

NID,I

'

N

ID

,I

m

Nl

a,1

m

N/Dil

m

NIO

,I

m NIOil

."

N/D

il

."

,.

2. 2.

.

..

50

/-

.

25

,.

25

2

.

.

7&

/60 501 -

50

.

JO

20

2.

2.

2.

>2

713

1-

501-

75/ -

501-

,.

25 25

25 25

B51-

65/ -

75/ - 501-

50

JO

2.

30 2. 30 2.

75/ -

501

-

,.

25 25 25

75/ - 501-

.

25

,.

25

,.

25

85

65

/-

50

.

SO

,.

30

S

f

50

/-

SO

,.

0

,.

15f 50 /-

75

/- 501-

50

,.

75/-

50

1-

75

/-

501- 75/60 501-

15/- SO/ -

75/ - 501- 75

/-

501-

75

/-

SO

/- 75/ -

501-

75

/-

501-

85 /-

65/

-

75

/-

501

-

'51

-

50

/-

15

I

851

-

65

/-

851 -

651-

85

/-

65

/-

651- 85 /- 65/- 85

/-

65

/-

100 h .. ' ' ' . / .u/ll; ,' . , ould nOf

uned

SOOO .,.,,,e" f.

15 ·

,

,,,d 1 r ~ . J ' ' ' . 111.111 ' u em

.

hould

nOI eX

;eed 4()(}()

m{Jt'n .

For . ,gll1''', oI'l1 (; iH: or b;mlr .

Ihe .m

gle·

ha

. e

k ~ a , '041 '9 3 10

obI

' II,,,

I1Q

.. l l 1 n r

3· , .11

,. ng. and mul /l ' Ih

''''9Ie. h .

by 1

131

0 o

m ,,,

I

he

nJ

l 1m 3· ha. ~ o l l ~ g t I 'al,n9_ SeIeOO,

, ... 0 ' .

'

Fig. 38. Proposed ch

aracle

rislil;S 01 150 ·, 200 ·,

an

d 3OO

rated 2400·1960 ~ o l


24/35

OF SHUNT CAPACITORS

Application guide for group-fusing capacitor banks with General Electric universal cab le-type and oil

cutout fuse link ratings N, OIL, K, and T types

FlOA.TING ·WYE CONNECTION

CAPACITOR BANKS WITIi

25.

50 ·

OR l00

· KVAR

UNITSIt

4160

Volt.

4800 Voh.

7200 Voh.

8320 Vol . 12470 Volts 13200 Vol .

13800 V"II>

J. h

.. Ky

. "

NIO,I

'

"1/0,1

'

NI

Oil

'

N{Oil

'

NIOil

'

NIOil

'

1,0,\

'

,

-

- -

40130

' ' ' '

,

,

,

'

45140

' '

'

'

75160

'

'

'

85175 45/50

'

' ' ' '

'

,. -

-

85/-

-

40/ -

' '

-

'

951-

-

75/60

'

'

.,

,.-

75160

'

451.0

'

4

5

40

85/ -

'

'

45

150

'

45

150

'

''''

95/-

-

85/-

~ I '

,

'

'

951-

-

,.-

'

~ I O O

' ''''' '

00

'

'

95/_

-

75 60

'

75 60

'

-

'

'

' '

'

151-

,. -

151_

'

125

851

-

'

'

'

851-

'

,.-

'

75/-

'

215 -

851 -

'

85

1-

'

,.-

-

,. -

-

,.-

425

,.-

-

95

/

-

,

'

,. -

-

- Application guide for group-fusing capacitor banks with General Electr ic universal cable-type and oil

cutout

fuse link rat ings N, OIL, K, and "TH types

·WVE

AND DELTA CONNECTIONS

I

TOR

BANI{S

WITH

150-, 200· AND 300·I( VAR UNITS

'

'

'

''''

''''''

00 ' / -

100/ _ 85/100

200'/

-

2 - ~ , . o c up ,

..

_

a/xl

. 25()(}ampe

Orf circulr curren .

1

>

15

25/25

4(1/40

'''''

5/65

95/95

100/ '00

125/ 100/ 1

00

125/

100/100

150/ 140/ 1401

150/

140/1401

200'/

-

e 20 - Application guide for group-fusing capacitor banks with General El

ect

r

ic

universal cable-type and o

il

cutout fuse link ratings

N,

"OIL

, K,

and

T

types

FLOATtN

G·WVE

CONNECT

I ONS

CAPACITOR SA NKS WITH 150-

zoo.

ANa 3

00

I{VAR UNITS

3·pIo_

4160 Votu

4800 VolU

7200

Vot .. 8320 Vol "

12.410

Vol

13.200 Vott. 13.900 Vol ..

K•• •

N/o;l

'

N/o;l

,.

N/o;l

'

N/o;l

'

N/o;l

'

NfOil

'

N/o;l

'

.'

951100

'''''

,. -

65/65

'

40140

"''''

40140

,.'

25125

;ro/20

-

20120

'

- -

- -

75175 751€0

.,,'

45140

:1()/30

4

0/40

25125

2 >125

'

- -

-

-

100/100

-

,. -

,.'

'

'

,.'

"''''

"'-

40/

40

,

'

- -

- -

- -

-

-

8 >1100

65165

,. - 65165

,.-

'

'

- -

- -

-

- -

-

951100

'

,. - 65165

,.- 6 >165

-

- -

- -

-

1001100

-

10011

00

- -

VIII LI HTNIN PROTECTION OF DISTRIBUTION SYSTEM

A.

Primary Distribution Systems

Continual research in the laboratory and in the field on

lightning and its effects on circuits and apparatus has established

the fundamentals of lightning

protection

so well

that the

careful

selection

and

application of modern arresters will provide

distribution systems with a high degree of immunity from

lightning troubles.

Adequate lightning protection of distribution systems

depends upon three major considerations:

1. The selection of distribution transformers

and

other

distribution

equipment that

have an insulation strength

to

lightning voltages

not

less than present·day basic insula·

tion levels.

2. The selection of arrester ra t ings which will limit

the

lightning stress

to

a value well below the standard

impulse-withstand level of

ap

paratus .

3. The effective application of the arresters, by mounting

them in close

shunt

relation with the apparatus

to

be

protected and, whenever possible, interconnecting

the

primary arrester ground to transformer secondary neutral.

1. Impulse Withstand Level

to

be P

rotected

ANSI basic in sulation levels and withs tand test values for

electrical apparatus are shown in Table 21. For example, this

table shows

that

the primary winding of a 15·kV voltage class

distribution transformer must withstand a

1.2

x 50

tlS

impulse

full ·wave test of

95

-kV crest

and

a chopped·wave

test

of 11O·kV

crest.

Conservative protection for a distribution transformer

throughout

its service life generally requires

get-1008l distribution data book

Documents