ABB Circuit Shield 87B User manual

IB

7.6

.

1.7

-

7

Issue

C

A

llll

*

IM

»

INSTRUCTIONS

High

Impedance

Differential

Relay

©

CIRCUIT

0

SHIELD

Type

87

B

Catalog

Series

419

B

£

HIGH

-

IMPEDANCE

OIFPERENTIAI

RELAY

*

®

0

2

SQ

•

*

a

too

.

t

?

s

#

'

400

TR

#

VOLTS

AC

RMS

SET

TES

1

ABB

Power

TSD

Company

A

-

f n

.

own

P

.

,

USA

v

.

-

;

Courtesy of NationalSwitchgear.com

High

-

Impedance

Differential

Relays

IB

7.6

.

1.7

-

7

Page

2

TABLE

OF

CONTENTS

Page

2

Page

2

Page

3

Page

6

Page

11

Page

14

Introduction

Precautions

Placing

Relay

into

Service

Application

Data

Testing

.

Obsolete

Models

INTRODUCTION

These

instructions

contain

the

information

required

to

properly

install

,

operate

and

test

the

ABB

Type

87

B

high

-

impedance

single

phase

differential

relay

.

The

Type

87

B

relay

is

a

high

-

speed

or

instantaneous

differential

voltage

device

intended

primarily

for

bus

differential

protection

.

High

current

sensitivity

also

allows

the

relay

to

be

used

for

differential

protection

of

resistance

grounded

systems

and

machines

or

reactors

.

The

relay

contains

voltage

-

limiting

resistors

(

varistors

)

which

limit

voltage

across

its

input

terminals

to

a

safe

value

during

system

faults

.

The

relay

is

housed

in

a

case

suitable

for

conventional

semi

-

flush

panel

mounting

.

The

unit

offers

totally

drawout

construction

with

integral

test

facilities

.

Current

transformer

shorting

is

accomplished

by

a

direct

-

acting

spring

and

blade

assembly

upon

removal

of

the

relay

from

its

case

.

Sequenced

disconnects

eliminate

any

possibility

of

nuisance

tripping

during

withdrawal

or

insertion

of

the

relay

.

A

target

indicator

is

mounted

on

the

front

panel

.

The

target

is

reset

by

means

of

a

pushbutton

extending

through

the

relay

cover

.

Control

voltage

must

be

present

to

reset

the

target

.

Earlier

models

,

catalog

series

219

B

are

covered

in

IB

7.6

.

1.7

-

5

.

PRECAUTIONS

The

following

precautions

should

be

taken

when

applying

these

relays

:

1

.

Incorrect

wiring

may

result

in

damage

.

Be

sure

wiring

agrees

with

the

connection

diagram

for

the

particular

relay

before

the

relay

is

energized

.

Be

sure

control

power

is

applied

in

the

correct

polarity

before

applying

.

2

.

Apply

only

the

rated

control

voltage

marked

on

the

relay

front

panel

.

The

proper

polarity

must

be

observed

when

the

DC

control

power

connections

are

made

.

3

.

Do

not

apply

high

voltage

tests

to

solid

state

relays

.

If

a

control

wiring

insulation

test

is

required

,

withdraw

the

relay

from

the

case

before

applying

test

voltage

.

4

.

A

lockout

relay

(

e

.

g

.

type

LOR

,

HEA

,

or

WL

)

must

be

used

to

short

circuit

the

input

signal

side

of

relay

87

B

upon

operation

of

the

differential

circuit

due

to

faults

within

the

protected

zone

.

5

.

The

entire

circuit

assembly

of

the

relay

is

removable

.

The

unit

should

insert

smoothly

.

Do

not

use

excessive

force

.

6

.

Follow

test

instructions

to

verify

that

relay

is

in

proper

working

order

.

If

a

relay

is

found

to

be

inoperative

,

return

to

factory

for

repair

.

Immediate

replacement

of

the

relay

can

be

made

available

from

the

factory

;

identify

by

catalog

and

serial

numbers

.

We

suggest

that

a

complete

spare

relay

be

ordered

as

a

replacement

,

and

the

inoperative

unit

be

repaired

and

retained

as

a

spare

.

7

.

CAUTION

:

Since

troubleshooting

entails

working

with

energized

equipment

,

caution

should

be

taken

to

avoid

personal

shock

.

Only

competent

technicians

familiar

with

good

safety

practices

should

services

these

devices

.

Courtesy of NationalSwitchgear.com

High

-

Impedance

Differential

Relays

IB

7.6

.

1.7

-

7

Page

3

PLACING

THE

RELAY

INTO

SERVICE

L

RECEIVING

.

HANDLING

^

STORAGE

Upon

receipt

of

the

relay

(

when

not

included

as

part

of

a

switchboard

)

examine

for

shipping

damage

.

If

damage

or

loss

is

evident

,

file

a

claim

at

once

and

promptly

notify

Asea

Brown

Boveri

.

Use

normal

care

in

handling

to

avoid

mechanical

damage

.

Keep

the

relay

clean

and

dry

.

2

.

INSTALLATION

Mounting

:

The

outline

dimensions

and

panel

drilling

and

cutout

information

is

given

in

Figure

1

.

Terminal

and

basic

circuit

identification

will

be

found

in

Figure

2

.

Connections

:

A

typical

external

connection

diagram

showing

(

3

)

Type

87

B

relays

used

for

bus

differential

protection

is

shown

in

Figure

3

.

Wiring

and

interconnections

should

be

in

accordance

with

instructions

.

Current

transformer

polarities

MUST

be

as

shown

.

The

relays

have

metal

front

panels

which

are

connected

through

printed

circuit

board

runs

and

connector

wiring

to

a

terminal

at

the

rear

of

the

relay

case

.

The

terminal

is

marked

“

G

”

.

In

all

applications

this

terminal

should

be

wired

to

ground

.

A

lockout

relay

must

be

wired

as

shown

in

Figure

3

.

DC

must

be

connected

in

the

proper

polarity

as

shown

in

the

diagram

.

To

obtain

best

sensitivities

and

facilitate

lower

pickup

settings

,

the

junction

points

of

CT

leads

should

he

made

equidistant

from

all

CT

'

s

,

or

leads

of

equal

resistance

provided

.

3

.

SETTINGS

VOLTAGE

PICKUP

:

75

-

400

Volts

AC

RMS

,

settable

by

means

of

a

front

panel

switch

at

75

,

100

,

150

,

200

,

250

,

300

,

350

or

400

volts

.

TEST

FEATURE

:

A

built

-

in

test

push

button

is

provided

for

operational

trip

tests

and

mounted

behind

the

removable

front

cover

.

When

using

the

built

-

in

test

switch

,

release

the

button

as

soon

as

the

87

B

operates

.

If

the

button

is

held

in

,

the

relay

will

continually

repeat

its

trip

and

reset

functions

rapidly

,

and

will

appear

to

chatter

.

RESET

:

The

relay

does

not

require

manual

reset

as

it

restores

itself

to

functional

status

upon

clearing

of

the

faults

and

resetting

of

the

lockout

relay

.

The

operation

indicator

is

of

the

memory

type

and

can

be

reset

after

a

fault

or

test

without

front

cover

removal

.

Courtesy of NationalSwitchgear.com

IB

7.6

.

1.7

-

7

Page

4

High

-

Impedance

Differential

Relays

TRIMMER

:

A

vernier

marked

pickup

inside

the

relay

on

the

upper

printed

circuit

board

allows

fine

calibration

of

pickup

settings

at

selected

switch

positions

.

4

.

Initial

Check

After

wiring

is

completed

and

checked

,

apply

control

power

and

reset

the

operation

indicator

.

If

the

indicator

cannot

be

reset

,

recheck

connections

,

voltage

and

polarity

.

Do

not

attempt

any

other

tests

until

wiring

errors

are

corrected

.

Verify

ratio

of

current

transformers

.

Check

polarity

at

CT

'

s

and

connections

to

the

relays

.

Exercise

test

push

button

to

check

proper

operation

of

87

B

and

lockout

relays

.

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SO

209.33

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NOTE

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DIMENSIONS

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Relay

Outline

and

Drilling

Figure

1

:

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STATION

GROUND

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VOLTAGE

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*

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o

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o

10

o

.

86

<

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>

(

-

)

Figure

2

:

Basic

Relay

Connections

419

B

Series

Units

Courtesy of NationalSwitchgear.com

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L

.

I

87

B

High

Impedance

Bus

Differential

Relay

,

Figure

3

s

Typical

External

Connections

,

Catalog

Series

419

B

,

for

Protection

of

Multiple

Bus

Sections

with

Bus

Ties

.

td

ON

:

p

:

00

CD

L

/

\

Courtesy of NationalSwitchgear.com

High

-

Impedance

Differential

Relays

IB

7.6

.

1.7

-

7

Page

6

SPECIFICATIONS

75

-

400

V

RMS

,

1500

Watt

-

seconds

Ratings

:

Input

Circuit

Table

1

;

Input

Impedance

and

Sensitivity

Current

Sensitivity

(

*

)

Primary

Amps

4000

:

5

2000

:

5

Pickup

Input

Resistance

(

burden

)

Ohms

±

10

%

Pickup

Current

A

.

RMS

±

10

%

Peak

Volts

(

Sine

)

Dial

1200

:

5

Setting

V

.

RMS

CT

20

12

106.1

1430

0.05

40

75

14

48

24

100

141.4

1600

0.06

19

64

32

150

212.1

1820

0.08

40

24

1950

0.10

80

200

282.8

48

29

96

250

353.6

2050

0.12

34

112

56

300

424.3

2120

0.14

38

128

64

495

2170

0.16

350

72

43

2210

144

400

565.7

0.18

(

*

)

System

current

values

are

listed

for

reference

only

and

represent

contribution

of

all

power

sources

.

Magnetizing

current

of

CT

'

s

is

not

included

.

Voltage

Pickup

:

±

5

%

of

setting

at

25

°

C

.

Tolerance

:

Operating

Time

:

Total

trip

time

:

23

-

40

milliseconds

(

includes

20

-

30

msec

,

time

of

the

lockout

relay

and

3

-

10

msec

,

operating

time

of

87

B

relay

)

.

Input

Withstand

:

150

Volts

RMS

continuous

400

Volts

RMS

for

5

minutes

1500

Wattsec

.

max

.

at

voltage

-

limiting

conditions

(

internal

system

faults

)

.

25

/

50

/

60

Hz

.

Frequency

:

Voltage

Limiting

:

1200

-

1500

Volts

instantaneous

at

input

currents

in

excess

of

0.5

-

1.0

ampere

.

Input

-

to

-

output

isolation

:

7500

V

peak

.

Dielectric

:

Catalog

Number

models

available

for

Control

Power

:

419

B

0002

419

B

0012

419

B

0022

419

B

0032

419

B

0042

419

B

0052

419

B

0082

419

B

0092

Drain

-

8

ma

(

stand

-

by

)

Drain

-

8

ma

(

stand

-

by

)

.

Drain

-

8.5

ma

(

stand

-

by

)

.

Drain

-

1

lma

(

stand

-

by

)

Drain

-

9.2

ma

(

stand

-

by

)

.

Drain

-

lOma

(

stand

-

by

)

.

Drain

-

12

ma

(

stand

-

by

)

.

Drain

-

18

ma

(

stand

-

by

)

.

+

20

%

-

50

%

+

20

%

-

50

%

+

20

%

-

50

%

+

20

%

-

50

%

+

20

%

-

50

%

+

20

%

-

50

%

+

20

%

-

50

%

+

20

%

-

50

%

110

Vdc

175

Vdc

220

Vdc

48

Vdc

125

Vdc

250

Vdc

32

Vdc

24

Vdc

Courtesy of NationalSwitchgear.com

High

-

Impedance

Differential

Relays

IB

7.6

.

1.7

-

7

Page

7

Output

Circuit

Contact

Rating

at

:

250

vdc

125

vdc

Tripping

Continuous

Break

30

Amperes

5

Amperes

0.3

Amperes

30

Amperes

5

Amperes

0.1

Amperes

More

than

3000

V

,

IMhz

.

bursts

at

60

Hz

repetition

rate

continuous

.

Transient

Immunity

;

Operating

Temperature

Range

:

Minus

-

30

to

+

70

degrees

C

.

UL

File

No

.

E

103204

UL

Recognized

:

PRINCIPLE

OF

OPERATION

The

Type

87

B

differential

relay

contains

solid

-

state

circuits

and

offers

high

-

speed

and

sensitive

protection

against

faults

within

the

protected

zone

of

substations

or

equipment

.

Its

input

presents

a

high

impedance

burden

to

current

transformers

(

see

table

1

)

for

secondary

differential

currents

below

0.5

amperes

and

corresponding

burden

voltages

below

1000

volts

peak

.

Leakage

current

through

the

relay

varistors

at

these

levels

is

negligible

.

The

voltage

pickup

setting

is

made

by

means

of

a

switch

and

trimmer

potentiometer

in

a

voltage

divider

circuit

.

The

relay

responds

to

modified

instantaneous

voltage

increase

across

its

terminals

above

the

set

point

during

internal

faults

.

The

pickup

voltage

should

be

set

above

the

moderate

voltages

which

may

occur

under

external

or

through

-

fault

conditions

due

to

unequal

performance

or

saturation

of

CT

'

s

.

Filter

and

delay

circuits

are

provided

against

system

transients

,

RFI

,

and

flux

exchange

between

current

transformers

.

The

relay

is

equipped

with

voltage

-

limiting

power

resistors

(

metal

oxide

varistors

)

to

limit

the

input

voltage

to

safe

values

during

internal

system

faults

.

Input

burden

at

heavy

faults

is

in

essence

,

a

relatively

high

dc

voltage

in

series

with

a

resistance

of

a

few

ohms

which

practically

does

not

impede

the

build

up

of

CT

summation

currents

.

Hence

,

the

relay

absorbs

instantaneous

power

in

the

order

of

kilowatts

while

responding

to

high

currents

and

has

assigned

wattsecond

limits

.

The

energy

delivered

by

current

transformers

depends

on

their

saturation

voltage

(

or

VA

rating

)

,

ratio

,

and

fault

current

magnitude

.

The

Type

87

B

relay

is

primarily

designed

to

operate

a

fast

lockout

relay

which

,

in

turn

,

short

circuits

the

relay

inputs

and

trips

associated

circuit

breakers

.

The

input

side

of

the

relay

is

isolated

from

the

output

circuits

by

an

optocoupler

.

The

output

side

consists

of

a

dry

contact

and

associated

clamping

,

delay

,

polarity

and

power

supply

circuits

.

A

target

is

provided

to

give

a

permanent

indication

of

relay

system

operation

and

is

reset

by

means

of

the

front

panel

push

-

button

.

The

built

-

in

test

feature

allows

operational

trip

test

of

the

Type

87

B

and

lockout

relay

.

When

a

differential

trip

occurs

,

the

output

contact

is

driven

closed

for

a

minimum

of

200

milliseconds

(

400

typical

)

then

automatically

resets

.

If

trip

level

input

is

maintained

,

the

relay

will

continue

to

cycle

through

the

trip

and

reset

functions

.

Courtesy of NationalSwitchgear.com

High

-

Impedance

Differential

Relays

IB

7.6

.

1.7

-

7

Page

8

APPLICATION

The

Type

87

B

is

a

single

-

phase

relay

of

the

high

-

impedance

high

-

speed

type

.

It

is

used

in

well

known

differential

circuits

with

standard

current

transformers

.

Typically

,

three

type

87

B

relays

and

a

lockout

relay

are

required

in

standard

configurations

for

bus

differential

protection

against

phase

-

to

-

phase

and

phase

-

to

-

ground

faults

.

A

properly

set

relay

will

discriminate

between

external

(

through

feed

)

and

internal

system

faults

.

The

relay

is

a

voltage

actuated

device

but

its

pick

-

up

sensitivity

is

proportional

to

current

magnitudes

during

internal

faults

.

The

voltage

across

the

relay

input

is

practically

zero

in

symmetrical

circuits

during

normal

operation

,

hence

the

continuous

input

rating

is

of

less

importance

.

Moderate

voltage

may

appear

in

the

secondary

circuits

due

to

unequal

performance

or

saturation

of

some

CT

'

s

.

However

,

these

voltages

will

result

in

smaller

differential

currents

(

in

percent

)

than

in

schemes

with

low

impedance

differential

relays

.

Thus

,

high

differential

impedance

(

usually

several

orders

of

magnitude

higher

than

the

shunt

impedance

of

saturated

CT

'

s

)

leaves

current

transformers

force

-

coupled

through

their

secondaries

and

allows

better

discrimination

between

faults

.

Internal

faults

lead

to

summation

of

all

infeed

secondary

currents

in

the

relay

with

some

shunting

effect

of

idle

CT

secondaries

.

Relay

voltage

and

current

rise

rapidly

during

heavy

internal

faults

.

The

signal

,

while

being

voltage

-

limited

by

varistors

,

causes

the

relays

to

operate

and

self

-

protect

the

input

of

87

B

relay

until

circuit

breakers

trip

.

All

differential

relays

of

high

-

impedance

type

have

limited

input

current

or

energy

ratings

.

The

described

protection

can

be

conveniently

expanded

to

more

CT

'

s

if

breakers

are

added

to

the

existing

scheme

.

The

standard

Type

87

B

relay

does

not

contain

restraining

circuits

.

Applications

which

involve

either

lightning

arresters

(

directly

connected

to

the

bus

)

or

non

-

relayed

capacitors

with

grounded

mid

-

points

or

other

equipment

subject

to

high

magnetizing

inrush

or

non

-

canceled

infeed

should

be

referred

to

the

factory

.

Application

of

the

Type

87

B

relay

and

calculation

of

proper

settings

require

consideration

of

the

above

described

properties

of

the

scheme

.

In

general

and

to

provide

optimum

performance

,

attention

is

recommended

to

:

proper

selection

of

current

transformers

and

wiring

,

voltage

settings

above

voltages

and

transients

expected

under

external

fault

or

inrush

conditions

,

sensitivity

to

internal

faults

,

and

relay

withstand

at

maximum

fault

magnitudes

.

For

example

,

the

following

selection

procedures

can

be

adapted

for

a

given

bus

differential

protection

scheme

:

Voltage

Settings

-

External

Faults

The

relay

should

be

set

above

maximum

secondary

circuit

voltage

which

will

appear

during

external

faults

.

Assume

that

the

CT

of

a

faulted

feeder

or

load

breaker

is

completely

saturated

and

one

or

more

source

CT

'

s

are

forcing

current

through

its

secondary

winding

.

1

.

Identify

ratio

and

location

of

CT

'

s

.

Obtain

or

calculate

DC

resistance

of

the

secondary

winding

of

the

CT

and

two

-

way

lead

length

from

the

junction

point

to

the

farthest

CT

.

Correct

resistance

values

to

the

highest

ambient

or

operating

temperature

.

2

.

Obtain

interrupting

rating

of

the

largest

circuit

breaker

(

symm

.

A

RMS

)

referred

to

secondary

side

of

CT

'

s

.

3

.

Product

of

this

current

and

resistance

sum

obtained

above

is

symmetrical

AC

RMS

voltage

.

4

.

To

obtain

minimum

relay

setting

,

multiply

this

value

by

a

factor

(

e

.

g

.

2.5

)

which

will

account

for

safe

margins

,

DC

offset

,

resistance

tolerances

and

current

transfer

between

CT

’

s

.

5

.

The

voltage

thus

calculated

represents

the

minimum

safe

setting

of

the

relay

.

If

the

value

is

between

set

points

,

use

the

pickup

setting

.

Still

higher

settings

will

provide

additional

safety

margins

with

some

increase

in

detectable

internal

fault

magnitude

.

In

most

cases

,

the

voltage

pickup

of

the

87

B

relay

can

be

set

above

the

saturation

voltage

rating

(

knee

point

)

of

CT

’

s

.

Courtesy of NationalSwitchgear.com

High

-

Impedance

Differential

Relays

IB

7.6

.

1.7

-

7

Page

9

These

conservative

calculations

can

be

refined

to

produce

lower

settings

if

the

following

or

other

practical

conditions

are

considered

:

Maximum

fault

current

is

usually

lower

than

interrupting

ratings

.

Faulted

circuit

CT

'

s

of

standard

design

never

saturate

completely

.

Source

CT

'

s

may

enter

saturation

region

.

Phase

-

to

-

ground

external

fault

currents

in

resistance

grounded

systems

are

relatively

low

,

hence

3

-

phase

fault

currents

and

one

-

way

lead

resistance

become

the

controlling

factors

.

Junction

points

of

leads

may

not

be

equidistant

but

closer

to

CT

'

s

of

feeders

which

are

subject

to

external

faults

.

Withstand

-

Internal

Faults

The

thermal

withstand

of

the

relay

is

controlled

by

internal

dissipation

limits

.

Energy

depends

on

the

speed

of

the

differential

and

lockout

relay

operation

,

maximum

available

fault

current

,

and

CT

saturation

characteristics

.

In

general

,

the

wattsecond

rating

of

high

impedance

relays

of

any

type

should

be

checked

against

expected

energy

.

For

convenience

,

one

could

use

a

simplified

method

as

reflected

in

Table

2

that

is

based

on

limits

of

CT

saturation

voltages

with

respect

to

relay

currents

and

a

conservative

total

operating

time

of

40

milliseconds

(

from

inception

of

the

fault

to

closing

instant

of

the

lockout

relay

contacts

)

.

Table

2

Typical

Input

Current

and

Energy

Limits

Current

Transformers

Max

Current

Transformers

Max

system

fault

current

(

Symm

RMS

)

Max

.

relay

Current

(

Symm

RMS

)

Max

.

system

fault

current

(

Symm

RMS

)

Max

relay

Current

(

Symm

RMS

)

Current

Transformers

Max

system

fault

current

Symm

RMS

)

relay

Current

(

Symm

RMS

)

Minimum

Ratio

Max

.

Satur

.

Voltage

Minimum

Ratio

Minimum

Ratio

Max

Satur

.

Voltage

Satur

..

Voltage

170

A

240

V

1500

:

5

1200

:

5

800

:

5

50

KA

37.5

KA

25

KA

100

A

2500

:

5

2000

:

5

1500

:

5

50

KA

37.5

KA

25

KA

350

V

300

A

170

V

1000

:

5

800

:

5

500

:

5

50

KA

37.5

KA

25

KA

150

A

260

V

50

KA

37.5

KA

25

KA

90

A

2000

:

5

1500

:

5

1000

:

5

360

V

3000

:

5

2500

:

5

1500

:

5

50

KA

37.5

KA

25

KA

250

A

200

V

1000

:

5

800

:

5

500

:

5

135

A

50

KA

37.5

KA

25

KA

280

V

2000

:

5

1500

:

5

1000

:

5

50

KA

37

.

5

KA

25

KA

75

A

4000

:

5

2500

:

5

2000

:

5

400

V

50

KA

37.5

KA

25

KA

220

A

210

V

1200

:

5

1000

:

5

600

:

5

50

KA

37.5

KA

25

KA

125

A

290

V

2000

:

5

1500

:

5

1000

:

5

50

KA

37.5

KA

25

KA

62

A

440

V

4000

:

5

3000

:

5

2000

:

5

50

KA

37.5

KA

25

KA

200

A

220

V

1500

:

5

1000

:

5

800

:

5

50

KA

37.5

KA

25

KA

310

V

110

A

2500

:

5

2000

:

5

1200

:

5

50

KA

37.5

KA

25

KA

40

A

600

V

(

*

)

50

KA

37.5

KA

25

KA

(

*

)

4000

:

5

(

*

)

CT

'

s

in

this

range

are

not

widely

available

due

to

limited

window

area

.

Consult

factory

.

If

the

maximum

fault

current

(

in

symmetrical

RMS

amperes

)

and

the

ratio

are

known

,

the

selected

saturation

voltage

of

any

CT

should

not

be

higher

than

indicated

on

the

corresponding

line

.

Conversely

,

the

CT

ratio

should

not

be

lower

than

one

shown

for

corresponding

values

of

the

system

fault

current

and

CT

saturation

voltage

.

Intermediate

values

can

be

obtained

by

interpolation

.

Alternatively

,

the

energy

can

be

accurately

calculated

from

the

instantaneous

product

of

secondary

'

current

and

voltage

pulses

.

One

should

bear

in

mind

,

however

,

that

the

total

circuit

is

not

linear

during

faults

.

Courtesy of NationalSwitchgear.com

IB

7.6

.

1.7

-

7

Page

10

High

-

Impedance

Differential

Relays

As

an

approximation

,

note

that

the

relay

input

voltages

are

approaching

square

shape

and

currents

triangular

pulse

form

at

high

internal

faults

.

Thus

,

the

product

of

CT

secondary

RMS

current

(

max

.

internal

fault

,

symmetrical

)

and

squared

value

of

CT

Saturation

RMS

voltage

multiplied

by

a

factor

30

X

10

'

6

is

a

measure

of

wattsecond

energy

per

pulse

that

is

absorbed

by

the

relay

.

This

value

that

is

multiplied

by

the

maximum

expected

number

of

pulses

should

be

less

than

relay

Wsec

.

rating

.

Note

that

pulses

occur

every

half

cycle

and

their

number

depends

on

the

operating

time

of

the

lockout

relay

to

the

contact

closing

.

Therefore

,

fast

lockout

relays

are

preferred

.

Current

Sensitivity

-

Internal

Faults

Since

the

varistor

current

within

the

pickup

range

of

the

relay

is

negligible

,

minimum

fault

current

to

trip

is

controlled

only

by

the

relay

burden

current

and

the

magnetizing

currents

of

current

transformers

.

Obtain

relay

Current

from

Table

1

and

add

to

the

sum

of

magnetizing

currents

of

all

CT

'

s

in

the

circuit

at

selected

pickup

voltage

(

consult

CT

magnetizing

curves

)

.

If

all

CT

'

s

are

identical

,

one

could

also

check

the

approximate

number

of

circuits

or

breakers

,

that

can

be

connected

to

the

relay

at

a

desired

current

sensitivity

and

voltage

setting

.

To

obtain

the

number

,

subtract

the

relay

current

from

the

required

fault

current

sensitivity

and

divide

by

the

magnetizing

current

of

one

CT

.

Current

Transformers

-

Wiring

The

relay

is

designed

for

use

with

dedicated

CT

'

s

.

Toroidal

or

bushing

type

current

transformers

with

low

leakage

impedance

are

preferred

.

All

current

transformers

must

be

of

the

same

ratio

,

and

preferably

,

have

the

same

relaying

class

rating

(

saturation

voltage

)

.

Highest

available

CT

tap

is

recommended

to

assure

that

the

secondary

winding

is

fully

distributed

around

the

core

.

The

best

sensitivity

will

be

obtained

if

CT

lead

resistances

to

the

junction

point

are

minimized

and

the

junction

is

equidistant

in

lead

length

from

all

CT

'

s

.

There

should

be

only

one

ground

connection

in

the

secondary

connection

.

See

Figure

3

on

Page

5

.

CT

polarity

and

recommended

connections

should

be

observed

.

A

lockout

relay

should

be

used

as

shown

.

The

user

should

select

current

transformers

,

wiring

,

and

terminations

that

are

capable

of

withstanding

circuit

voltages

encountered

during

faults

.

If

CT

secondaries

are

additionally

protected

by

gaps

or

varistors

,

their

trigger

or

threshold

voltage

should

not

be

less

than

1600

-

2000

volts

.

Courtesy of NationalSwitchgear.com

ABB Circuit Shield 87B User manual

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