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Instruction

Leaflet

41

-

347.1

S

A

mi

MINI

ABB

Power

T

&

D

Company

Inc

.

Relay

Division

Coral

Springs

,

FL

33065

Type

HU

,

HU

-

1

and

HU

-

4

Transformer

Differential

Relays

Effective

:

April

1991

Supersedes

41

-

347.1

R

,

Dated

April

1987

(

|

)

Denotes

Change

Since

Last

Issue

File

No

.

E

103204

the

restraint

transformers

of

the

HU

and

HU

-

1

relays

are

connected

in

parallel

,

and

the

I

IT

pickup

of

these

relays

is

ten

times

the

relay

tap

value

.

On

the

other

hand

,

the

rectified

outputs

of

the

restraint

transform

-

ers

of

the

HU

-

4

relay

are

connected

in

series

,

and

the

IIT

-

unit

for

this

relay

is

set

at

fifteen

times

the

tap

value

.

Otherwise

,

the

three

relays

are

identical

.

Three

-

winding

banks

normally

require

the

HU

-

1

re

-

lay

,

although

the

auto

transformer

application

uses

the

HU

if

the

tertiary

is

not

loaded

.

The

HU

-

4

is

par

-

ticularly

applicable

to

protect

a

transformer

and

bus

section

combination

.

It

also

may

be

applied

to

three

-

winding

transformers

with

one

side

connected

to

two

breakers

.

CAUTION

Before

putting

relays

into

service

,

remove

all

blocking

which

may

have

been

inserted

for

the

purpose

of

securing

the

parts

during

shipment

,

make

sure

that

all

moving

parts

operate

freely

,

inspect

the

contacts

to

see

that

they

are

clean

and

close

properly

,

and

operate

the

relay

to

check

the

settings

and

electrical

connections

.

These

instructions

apply

to

the

following

types

of

relays

:

•

HU

•

HU

-

1

The

HU

,

HU

-

1

and

HU

-

4

are

available

with

a

sensi

-

tivity

of

either

30

%

or

35

%

times

tap

.

The

30

%

sen

-

sitivity

relay

satisfactorily

handles

up

to

15

%

mis

-

match

(

e

.

g

.

,

±

10

%

transformer

tap

changing

plus

5

%

ct

mismatch

)

.

The

35

%

sensitivity

relay

handles

as

much

as

20

%

mismatch

.

See

Figures

13

and

14

for

a

comparison

of

the

characteristics

of

the

two

sensitivities

.

Any

of

the

relays

may

be

recalibrated

in

the

field

to

obtain

either

characteristic

.

•

HU

-

4

1

.

APPLICATION

The

types

HU

,

HU

-

1

,

and

HU

-

4

relays

are

high

speed

relays

used

in

the

differential

protection

of

transformers

.

These

relays

can

be

applied

where

the

magnetizing

inrush

current

to

the

transformer

is

severe

.

Current

transformer

ratio

error

should

not

exceed

10

%

with

maximum

symmetrical

external

fault

cur

-

rent

flowing

and

the

maximum

symmetrical

error

cur

-

rent

which

is

flowing

in

the

differential

circuit

on

ex

-

ternal

faults

should

not

exceed

10

times

relay

tap

setting

.

The

types

HU

,

HU

-

1

,

and

HU

-

4

relays

have

two

,

three

,

or

four

restraint

transformers

,

respectively

,

and

associated

rows

of

taps

.

The

rectified

outputs

of

Ordinarily

the

30

%

sensitivity

relay

will

suffice

;

how

-

ever

,

where

ct

mismatch

is

abnormally

high

or

where

the

transformer

tap

-

changing

range

exceeds

±

10

%

,

this

calibration

may

be

too

sensitive

.

Z

CONSTRUCTION

The

types

HU

,

HU

-

1

and

HU

-

4

relays

consist

of

a

dif

-

ferential

unit

(

DU

)

,

a

harmonic

restraint

unit

(

HRU

)

,

an

indicating

instantaneous

trip

unit

(

NT

)

and

an

All

possible

contingencies

which

may

arise

during

installation

,

operation

,

or

maintenance

,

and

all

details

and

variations

of

this

equipment

do

not

purport

to

be

covered

by

these

instructions

.

If

further

information

is

desired

by

purchaser

regarding

this

particular

installation

,

operation

or

maintenance

of

this

equipment

,

the

local

Asea

Brown

Boveri

representative

should

be

contacted

.

Printed

in

USA

Courtesy of NationalSwitchgear.com

ro

r

i

*

NI

M

&

Operating

Ckt

.

Resistor

{

DU

)

To

Restraint

Transf

.

4

I

*

Operating

Ckt

.

Resistor

(

DU

)

Hi

t

Harmonic

Restraint

Unit

(

MRU

)

ik

.

AT

-

'

L

.

.

Harmonic

Restraint

Unit

IHRU

)

m

jgj

r

*

i

t

T

.

Differential

Unit

(

DU

)

jj

R

P

?

K

s

Parallel

Reactor

{

HRU

Operate

Filter

)

Differentia

!

Unit

(

DU

)

*

*

s

<

t

T

-

^

TAP

BLOCK

B

Restraint

Transf

.

t

jig

—

Restraint

Transf

.

2

3

—

Restraint

Transf

.

3

(

HU

-

1

Only

)

!

:

-

h

t

\

x

*

TAP

Bl

OCK

Restraint

Transf

.

4

Restraint

Transf

.

t

Restraint

Transf

.

2

Restraint

Transf

.

3

1

’

f

’

VT

r

*

*

t

,

•

i

k

-

j

*

»

1

L

p

igrlt

!

•

»

!

>

§

>

§

’

'

rf

*

1

*

1

*

'

*

1

*

1

*

1

*

LL

I

si

pR

*

lvi

\

*

k

i

i

-

jj

>

li

Restraint

Transformers

{

DU

)

Indicating

Contactor

Switch

(

ICS

)

Restraint

Transformer

(

DU

)

i

w

\

t

%

*

Indicating

Instantaneous

Trip

(

IIT

)

Indicating

Contactor

Switch

(

ICS

)

>

'

:

>

!

|

«

M

Indicating

Instantaneous

Trip

(

IIT

)

To

Restraint

Transf

.

3

(

HU

-

1

Only

)

To

Restraint

Transf

.

2

To

Restraint

Transf

.

1

To

Restraint

Transf

.

3

To

Restraint

Transf

.

2

To

Restraint

Transf

.

1

Figure

1

.

Type

HU

,

HU

-

1

Relays

(

Front

View

)

Figure

2

.

Type

HU

-

4

Relay

(

Front

View

)

Courtesy of NationalSwitchgear.com

...

I

\

s

m

§

:

*

[

3

•

•

f

|

|

f

DU

Restraint

-

Scries

Filter

-

Reactor

(

MRU

Restraint

)

,

iL

*

»

Parallel

Fiiter

-

Reaotor

(

Operate

MRU

)

gif

;

''

7

a

:

.

v

-

.

v

*

-

~

Parallel

Filter

-

Reactor

(

HRU

Restraint

)

m

•

;

m

Series

Filter

-

Reactor

(

Restraint

HRU

)

&

4

7

:

l

'

1

/

t

Parallel

Filter

-

Reactor

(

HRU

Restraint

)

t

.

Operating

Transf

.

(

HRU

)

-

-

i

Operating

Transf

.

(

HRU

)

.

:

t

Operating

Transf

.

(

DU

)

:

vj

j

Operating

Transf

.

(

DU

)

ISIS

*

-

.

7

.

..

E

3

L

»

M

>

J

r

»

M

»

i

L

*

«

*

J

•

1

5

<

3

V

..

=

s

-

v

-

i

’

'

V

,

Operating

Circuit

Filter

Capacitor

(

HRU

)

(

4

MFD

)

\

S

Operating

Circuit

Filter

Capacitor

(

HRU

)

(

4

MFD

)

T

l

:

R

1

Capacitor

--

0.45

MFD

HRU

Restraint

F

liter

Circuit

r

Capacitor

0.45

MFD

HRU

Restraint

F

it

ter

Circuit

&

a

»

£

*

4

«

(

4

Figure

4

.

Type

HU

-

4

Relays

(

Rear

View

)

Figure

3

.

Type

HU

,

HUH

Relays

(

Rear

View

)

Courtesy of NationalSwitchgear.com

I

.

L

41

-

347.1

S

indicating

contactor

switch

(

ICS

)

.

The

principal

parts

of

the

relays

and

their

locations

are

shown

in

Figures

1

to

7

.

rear

with

two

brass

spacers

and

silver

solder

.

These

non

-

magnetic

joints

represent

air

gaps

,

which

are

bridged

by

two

adjustable

magnetic

shunts

.

The

windings

are

wound

around

a

magnetic

core

.

The

ar

-

mature

is

fastened

to

this

core

and

is

free

to

move

in

the

front

air

gap

.

The

moving

contact

is

connected

to

the

free

end

of

a

leaf

spring

,

which

,

in

turn

,

is

fas

-

tened

to

the

armature

.

2.1

Differential

Unit

(

DU

)

The

differential

unit

of

these

relays

consists

of

re

-

straint

circuits

,

full

wave

rectifiers

,

saturating

operat

-

ing

transformer

,

and

a

dc

polar

unit

.

The

basic

differences

in

the

differential

unit

of

the

three

relays

is

in

the

restraint

circuit

.

The

restraint

circuit

of

the

HU

-

4

relay

consists

of

four

air

-

gap

restraint

transformers

and

four

full

wave

rec

-

tifiers

whose

outputs

are

connected

in

series

.

The

restraint

circuit

of

the

HU

-

1

relay

consists

of

three

air

-

gap

restraint

transformers

and

three

full

wave

rectifiers

whose

outputs

are

connected

in

parallel

.

The

restraint

circuit

of

the

HU

relay

consists

of

two

air

-

gap

restraint

transformers

and

two

full

wave

rec

-

tifiers

whose

outputs

are

connected

in

parallel

.

Each

of

the

restraint

transformers

and

the

operating

transformer

are

provided

with

taps

to

compensate

for

mismatch

of

line

current

transformers

.

These

taps

are

incorporated

in

the

relay

in

such

a

manner

that

changing

a

tap

on

a

restraint

transformer

auto

-

matically

changes

the

same

tap

on

the

operating

transformer

.

2.4

Indicating

Contactor

Switch

Unit

(

ICS

)

The

dc

indicating

contactor

switch

is

a

small

clapper

-

type

device

.

A

magnetic

armature

,

to

which

leaf

-

spring

mounted

contacts

are

attached

,

is

attracted

to

the

magnetic

core

upon

energization

of

the

switch

.

When

the

switch

closes

,

the

moving

contacts

bridge

two

stationary

contacts

,

completing

the

trip

circuit

.

Also

,

during

this

operation

,

two

fingers

on

the

arma

-

ture

deflect

a

spring

located

on

the

front

of

the

switch

,

which

allows

the

operation

indicator

target

to

drop

.

The

front

spring

,

in

addition

to

holding

the

target

,

provides

restraint

for

the

armature

and

thus

controls

the

pick

-

up

value

of

the

switch

.

2.5

Indicating

Instantaneous

Trip

Unit

(

NT

)

The

instantaneous

trip

unit

is

a

small

ac

operated

clapper

type

device

.

A

magnetic

armature

,

to

which

leaf

-

spring

mounted

contacts

are

attached

,

is

at

-

tracted

to

the

magnetic

core

upon

energization

of

the

switch

.

When

the

switch

closes

,

the

moving

contacts

bridge

two

stationary

contacts

completing

the

trip

cir

-

cuit

.

Also

,

during

the

operation

,

two

fingers

on

the

ar

-

mature

deflect

a

spring

located

on

the

front

of

the

switch

which

allows

the

operation

indicator

target

to

drop

.

A

core

screw

accessible

from

the

top

of

the

switch

provides

the

adjustable

pickup

range

.

3

.

OPERATION

The

types

HU

and

HU

-

1

relays

are

connected

to

the

protected

transformer

as

shown

in

Figures

10

and

11

.

The

HU

-

4

is

connected

to

the

protected

trans

-

former

as

shown

in

Figure

12

.

In

such

a

connection

the

relays

operate

to

protect

the

transformer

for

faults

internal

to

the

differential

zone

of

the

trans

-

former

,

but

not

for

faults

external

to

the

zone

.

Neither

do

the

relays

operate

on

magnetizing

inrush

currents

2.2

Harmonic

-

Restraint

Unit

(

HRU

)

The

harmonic

-

restraint

unit

of

the

HU

relays

consists

of

an

air

gap

operating

transformer

,

a

second

har

-

monic

block

filter

,

a

fundamental

block

second

har

-

monic

pass

filter

,

two

full

-

wave

rectifiers

,

indicating

instantaneous

trip

unit

,

varistor

,

and

a

dc

polar

unit

.

Taps

are

also

incorporated

in

this

unit

to

compen

-

sate

for

mismatch

of

the

line

current

transformers

.

Changing

a

tap

on

the

restraint

transformer

of

the

differential

unit

also

changes

the

tap

of

this

unit

.

2.3

Polar

Unit

The

polar

unit

consists

of

a

rectangular

shaped

mag

-

netic

frame

,

an

electromagnet

,

a

permanent

magnet

,

and

an

armature

.

The

poles

of

the

crescent

shaped

permanent

magnet

bridge

the

magnet

frame

.

The

magnetic

frame

consists

of

three

pieces

joined

in

the

4

Courtesy of NationalSwitchgear.com

I

.

L

41

-

347.1

S

associated

with

energization

of

the

transformer

even

though

these

currents

may

appear

as

an

internal

fault

.

To

avoid

these

false

operations

,

each

unit

of

the

relay

performs

a

separate

function

.

The

differen

-

tial

unit

(

DU

)

prevents

operation

on

an

external

fault

,

while

the

harmonic

-

restraint

unit

(

HRU

)

prevent

op

-

erations

on

magnetizing

inrush

currents

.

Hence

,

the

operation

of

the

relay

can

best

be

described

under

the

headings

of

external

fault

current

,

internal

fault

currents

,

and

magnetizing

inrush

currents

.

and

HU

-

1

relays

and

to

the

sum

of

the

restraint

cur

-

rent

flowing

in

the

HU

-

4

relay

.

The

sum

of

the

re

-

straint

current

flows

into

the

operating

transformer

and

produces

an

excess

of

operating

torque

,

and

the

differential

unit

operates

.

In

the

case

of

an

internal

fault

fed

from

one

source

only

,

the

fault

current

flows

in

one

restraint

trans

-

former

and

the

operating

transformer

.

An

excess

of

operating

torque

is

produced

on

the

differential

unit

and

it

operates

.

Faults

normally

appear

as

an

offset

sine

wave

with

a

decaying

dc

component

,

and

contain

very

few

har

-

monics

.

As

a

result

,

the

harmonic

-

restraint

unit

will

operate

during

internal

faults

to

permit

tripping

of

the

relay

.

For

heavy

internal

faults

,

the

indicating

instanta

-

neous

trip

unit

(

NT

)

will

operate

.

Since

this

unit

is

connected

to

an

air

gap

transformer

,

essentially

only

the

sine

wave

component

of

an

internal

fault

is

ap

-

plied

to

the

NT

unit

.

The

dc

component

of

the

fault

is

bypassed

by

the

transformer

primary

.

The

varistor

connected

across

the

dc

side

of

the

re

-

straint

rectifier

of

the

harmonic

restraint

unit

prevents

excessive

voltage

peaks

from

appearing

across

the

rectifiers

.

These

peaks

arise

through

transformer

ac

-

tion

of

the

harmonic

-

restraint

polar

-

unit

coils

during

heavy

internal

faults

.

The

varistor

has

a

large

value

of

resistance

for

low

voltages

,

while

presenting

a

low

value

of

resistance

for

high

voltages

.

This

character

-

istics

effectively

reduces

the

voltage

spikes

on

heavy

internal

faults

while

not

hampering

perfor

-

mance

during

inrush

,

where

the

voltage

is

consider

-

ably

lower

.

3.1

External

Fault

Currents

The

HU

family

of

relays

have

a

variable

percentage

characteristic

.

This

means

that

the

operating

current

required

to

close

the

contact

of

the

differential

unit

expressed

in

percent

of

restraint

varies

with

the

magnitude

of

the

larger

restraint

current

in

the

HU

and

HU

-

1

current

relays

and

with

the

sum

of

the

re

-

straint

current

in

the

HU

-

4

relays

.

Figures

13

and

14

illustrate

these

characteristics

.

To

use

these

curves

,

divide

each

restraint

current

by

the

appropriate

tap

and

enter

the

horizontal

axis

using

the

larger

or

larg

-

est

restraint

multiple

.

Then

enter

the

vertical

axis

,

us

-

ing

the

difference

of

the

restraint

multiples

.

With

the

relay

connected

as

shown

in

the

schematic

diagram

of

Figure

15

a

,

an

external

fault

causes

cur

-

rent

to

flow

in

the

air

-

gap

restraint

transformers

of

the

differential

unit

.

If

the

line

current

transformers

do

not

saturate

and

the

correct

ratio

matching

taps

ap

-

plied

,

no

effective

current

flows

in

the

operating

transformer

of

the

relay

.

Hence

,

only

contact

-

open

-

ing

torque

is

produced

on

the

differential

unit

.

On

heavy

external

faults

where

a

main

current

trans

-

former

saturates

,

current

flows

in

the

operating

cir

-

cuit

of

the

relay

.

With

such

a

condition

,

the

harmonic

-

restraint

unit

may

or

may

not

close

its

contacts

,

de

-

pending

upon

the

harmonics

present

in

the

false

op

-

erating

current

.

However

,

operation

of

the

relay

is

prevented

by

the

variable

percentage

characteristic

of

the

differential

unit

,

since

a

large

differential

cur

-

rent

is

required

to

close

its

contacts

during

heavy

ex

-

ternal

faults

.

3.3

Magnetizing

Inrush

Currents

Magnetizing

inrush

current

waves

have

various

wave

shapes

.

A

typical

wave

appears

as

a

rectified

half

wave

with

decaying

peaks

.

In

any

case

,

the

var

-

ious

wave

shapes

are

rich

in

harmonics

with

the

sec

-

ond

harmonic

predominant

.

Since

the

second

har

-

monic

is

always

present

in

inrush

waves

and

not

in

internal

fault

waves

,

this

harmonic

is

used

to

restrain

the

harmonic

-

restraint

unit

during

inrushes

.

The

dif

-

ferential

unit

may

or

may

not

close

its

contacts

,

de

-

pending

on

the

magnitude

of

the

inrush

.

3.2

Internal

Faults

In

the

case

of

an

internal

fault

as

shown

in

Figure

15

b

,

the

restraint

of

the

differential

unit

is

proportion

-

al

to

the

largest

restraint

current

flowing

in

the

HU

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Courtesy of NationalSwitchgear.com

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When

a

magnetizing

inrush

wave

is

applied

to

the

re

-

lay

,

the

dc

component

of

the

wave

is

bypassed

by

the

air

-

gap

operating

transformer

.

The

other

compo

-

nents

are

fed

into

the

filter

circuits

.

The

impedance

characteristics

of

these

filters

are

such

that

the

sec

-

ond

harmonic

component

flows

into

the

restraint

coil

of

the

polar

unit

,

while

the

other

harmonics

flow

into

the

operating

coil

.

The

polar

unit

will

not

close

its

contacts

unless

the

second

harmonic

content

is

less

than

15

percent

of

the

fundamental

component

.

be

approximately

1.0

volt

.

Use

Figure

17

if

the

pick

-

up

is

0.35

times

tap

.

Pickup

of

the

harmonic

-

restraint

unit

and

the

differ

-

ential

unit

is

either

30

or

35

%

of

tap

value

current

.

Pick

up

of

the

indicating

instantaneous

trip

unit

is

10

times

tap

value

current

for

the

HU

and

the

HU

-

1

re

-

lay

and

15

times

tap

value

current

for

the

HU

-

4

.

Components

of

the

harmonic

-

restraint

unit

are

se

-

lected

such

that

15

%

second

harmonic

will

prevent

operation

of

the

unit

.

This

factor

is

adequate

to

pre

-

vent

false

operation

on

inrushes

.

The

frequency

response

of

the

HU

and

HU

-

1

60

Hz

relays

is

shown

in

Figure

19

and

,

for

the

HU

and

HU

-

1

50

Hz

relays

is

shown

in

Figure

28

.

The

indicating

instantaneous

trip

unit

(

NT

)

will

not

op

-

erate

on

inrush

.

The

air

-

gap

transformer

will

bypass

Ihe

dc

component

of

the

inrush

thereby

reducing

the

magnitude

of

the

wave

applied

to

the

IIT

unit

.

If

the

inrush

has

an

initial

peak

of

16

times

tap

-

value

cur

-

rent

,

the

air

-

gap

transformer

will

reduce

this

peak

to

approximately

8

times

tap

value

on

the

secondary

of

the

transformer

.

4.1

Trip

Circuit

The

main

contacts

will

safely

close

30

amperes

at

250

volts

dc

,

and

the

seal

-

in

contacts

of

the

indicat

-

ing

contactor

switch

will

safely

carry

this

current

long

enough

to

trip

a

circuit

breaker

.

The

indicating

contactor

switch

has

two

taps

that

provide

a

pick

-

up

setting

of

0.2

or

2

amperes

.

To

change

taps

requires

connecting

the

lead

located

in

front

of

the

tap

block

to

the

desired

setting

by

means

of

a

screw

connection

3.4

Breaker

Maintenance

Before

some

of

the

ct

’

s

are

bypassed

for

breaker

maintenance

the

trip

circuit

should

be

opened

,

as

shown

in

Figures

9

through

12

.

Otherwise

the

false

-

unbalanced

current

will

cause

the

relay

to

trip

.

It

is

not

necessary

to

short

-

circuit

the

relay

operating

cir

-

cuit

since

it

has

an

adequate

continuous

-

current

rat

-

ing

.

(

See

“

Energy

Requirements

”

)

.

4

.

CHARACTERISTICS

Taps

are

incorporated

in

the

HU

family

of

relays

to

compensate

for

main

current

transformer

mismatch

.

These

taps

are

as

follows

:

2.9

,

3.2

,

3.5

,

3.8

,

4.2

,

4.6

,

5.0

,

8.7

.

To

measure

the

effective

unbalance

,

a

sensitive

low

-

reading

voltmeter

(

5000

ohms

per

volts

)

can

tempo

-

rarily

be

connected

across

the

operating

coil

resistor

(

at

top

of

case

)

.

With

a

perfect

balance

,

the

voltmeter

reading

will

be

zero

.

The

reading

should

not

exceed

the

values

indicated

by

the

15

%

mismatch

curve

at

Figure

16

when

the

relay

pickup

is

0.30

times

tap

.

If

the

amount

of

mismatch

is

measured

or

calculated

,

the

measured

voltage

can

be

checked

against

the

in

-

terpolated

value

from

the

curve

.

For

example

,

as

-

sume

that

the

larger

restraint

current

is

measured

as

1.5

tap

multiple

and

the

calculated

mismatch

is

7

%

.

Then

,

from

Figure

16

the

measured

voltage

should

5

.

SETTING

CAUTION

Since

the

tap

block

screw

carries

operating

cur

-

rent

,

be

sure

that

the

screws

are

turned

tight

.

In

order

to

avoid

opening

current

transformer

circuits

when

changing

taps

under

load

,

the

re

-

lay

must

be

first

removed

from

the

case

.

Chassis

operating

shorting

switches

on

the

case

will

short

the

secondary

of

the

current

transformer

.

The

taps

should

then

be

changed

with

the

relay

outside

of

the

case

and

then

reinserted

into

the

case

.

To

set

the

relay

,

calculations

must

be

performed

as

shown

under

“

Setting

Calculations

”

.

After

the

correct

tap

is

determined

,

connections

can

be

made

to

the

relay

transformers

by

placing

the

connector

screws

in

the

various

terminal

-

plate

holes

in

front

of

the

re

-

lay

.

Only

one

tap

screw

should

be

inserted

in

any

horizontal

row

of

taps

.

6

Courtesy of NationalSwitchgear.com

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5.1

Indicating

Contactor

Switch

(

ICS

)

No

setting

is

required

on

the

ICS

unit

except

the

se

-

lection

of

the

0.2

or

2.0

ampere

tap

setting

.

This

se

-

lection

is

made

by

connecting

the

lead

located

in

front

of

the

tap

block

to

the

desired

setting

by

means

of

the

connecting

screw

.

When

the

relay

energizes

a

125

-

or

250

-

volt

dc

type

WL

relay

switch

,

or

equiva

-

lent

,

use

the

0.2

ampere

tap

;

for

48

volt

dc

applica

-

tions

set

relay

in

2

tap

and

use

Type

WL

Relay

coil

S

#

304

C

209

G

01

or

equivalent

.

Trip

Circuit

Constants

Indicating

Contactor

Switch

(

ICS

)

6.2

Definitions

of

Terms

Ip

=

Primary

current

at

(

KVA

)

M

IR

=

Relay

input

current

at

(

KVA

)

M

IRH

,

IRL

.

IRI

ate

same

as

IR

except

for

high

,

low

and

intermediate

voltage

sides

respec

-

tively

.

Is

=

ct

secondary

current

at

(

KVA

)

M

T

=

relay

tap

setting

.

TH

,

TL

,

Tl

=

are

same

as

T

except

for

high

,

low

and

intermediate

voltage

windings

,

re

-

spectively

.

N

=

Number

of

current

transformer

turns

that

are

in

use

.

Np

=

N

/

NT

(

Proportion

of

total

turns

in

use

)

Nj

=

Current

transformer

ratio

,

full

tap

VCL

=

“

C

”

accuracy

class

voltage

ZA

=

Burden

impedance

of

any

devices

other

than

the

HU

,

HU

-

1

,

or

HU

-

4

relays

,

with

maximum

external

fault

current

flowing

.

•

ext

=

max

symmetrical

external

fault

current

in

sec

-

ondary

RMS

amperes

.

Zj

=

Total

secondary

burden

in

ohms

(

excluding

current

transformer

winding

resistance

.

)

0.2

ampere

tap

-

6.5

ohms

dc

resistance

2.0

ampere

tap

-

0.15

ohm

dc

resistance

5.2

Indicating

Instantaneous

Trip

(

IIT

)

No

setting

is

required

on

the

indicating

instanta

-

neous

trip

unit

.

This

unit

is

set

at

the

factory

to

pickup

as

follows

:

•

HU

/

HU

-

1

Relays

10

times

tap

value

current

•

HU

-

4

Relay

15

times

tap

value

current

6

.

SETTING

CALCULATIONS

Select

the

ratio

matching

taps

.

There

are

no

other

settings

.

In

order

to

calculate

the

required

tap

set

-

tings

and

check

current

transformer

performance

the

following

information

is

required

.

6.3

Calculation

Procedure

a

.

Select

current

transformer

taps

,

where

multi

-

ra

-

tion

types

are

used

.

Select

a

tap

to

give

approximately

5

amperes

at

maximum

load

.

This

will

provide

good

sensitivity

and

will

produce

no

thermal

problem

to

the

ct

.

,

the

leads

,

or

the

relay

.

Better

sensitivity

can

be

achieved

by

selecting

a

tap

to

give

more

than

5

amperes

if

a

careful

check

is

made

of

the

ct

,

the

leads

,

and

the

relay

capabil

-

ity

.

For

determining

the

required

continuous

rating

of

the

relay

,

use

the

expected

two

hour

maximum

load

,

since

the

relay

reaches

final

temperature

in

this

time

.

b

.

Calculate

the

relay

currents

,

IR

.

All

relay

currents

for

relay

tap

selection

should

be

based

on

the

same

KVA

capacity

.

c

.

Calculate

the

relay

current

ratio

(

s

)

using

the

low

-

est

current

as

reference

.

6.1

Required

Information

a

.

Maximum

transformer

power

rating

(

KVA

)

M

b

.

Maximum

external

fault

currents

c

.

Line

-

to

-

Line

voltage

ratings

of

power

transformer

(

VH

.

VI

.

VJ

d

.

Current

transformer

ratios

,

full

tap

(

Nj

)

e

.

Current

transformer

“

C

”

accuracy

class

voltage

(

or

excitation

or

ratio

correction

factor

curve

)

f

.

One

way

current

transformer

lead

resistance

at

25

°

C

(

RL

)

.

When

using

excitation

curve

,

include

ct

winding

resistance

.

g

.

Current

transformer

connections

(

wye

or

delta

)

ct

secondary

winding

resistance

,

Rs

-

7

Courtesy of NationalSwitchgear.com

I

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L

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S

d

.

Select

the

tap

ratio

as

close

as

possible

to

relay

current

ratio

from

Table

1

.

Choose

the

first

relay

tap

ratio

using

the

largest

current

ratio

from

step

3

.

The

other

tap

ratios

should

be

determined

us

-

ing

the

lower

tap

from

the

first

tap

ratio

as

reference

.

IR

should

not

exceed

relay

continuous

rating

as

defined

in

Energy

Requirement

Table

.

e

.

Check

IIT

operation

.

The

IIT

pickup

is

ten

times

the

relay

tap

value

for

the

HU

and

HU

-

1

,

or

15

times

tap

value

for

the

HU

-

4

.

Therefore

,

the

max

-

imum

symmetrical

error

current

which

is

flowing

in

the

differential

circuit

on

external

fault

current

due

to

dissimilar

ct

saturation

should

not

exceed

10

or

15

times

relay

tap

.

f

.

Determine

Mismatch

For

2

winding

banks

:

relay

ing

accuracy

classif

ication

.

If

the

“

C

”

accura

-

cy

is

used

,

performance

will

be

adequate

if

:

[

NpVci

-

(

lext

-

100

)

Rs

]

/

lext

is

greater

than

Zj

(

2

)

NOTE

:

Let

lext

=

100

where

maximum

external

fault

current

is

less

than

100

A

.

For

wye

-

connected

ct

:

Zj

=

lead

resistance

+

relay

burden

+

2

A

=

1.13

(

Rl

+

+

ZA

)

ohms

(

3

)

(

R

|

_

multiplier

,

1.13

,

is

used

to

account

for

0.15

temperature

rise

during

faults

.

proximation

.

Use

2

way

lead

resistance

for

single

phase

to

ground

fault

.

For

delta

-

connected

ct

:

an

ap

-

T

/

*

RL

_

\

\

VI

V

RH

0

)

%

mismatch

=

100

S

0.15

+

ZA

)

ohms

^

ZT

=

3

(

1.13

RL

+

where

S

is

the

smaller

of

the

two

terms

,

T

0.45

W

or

(

4

)

=

3.4

(

RL

+

T

+

3

Za

)

h

.

Examples

:

Refer

to

Tables

6

and

7

and

Figure

20

for

setting

ex

-

amples

.

For

3

winding

banks

:

Repeat

calculation

of

equation

(

1

)

and

apply

sim

-

ilar

equations

to

calculate

mismatch

from

the

intermediate

to

high

and

from

and

from

the

inter

-

mediate

to

low

voltage

windings

.

Where

tap

changing

under

the

load

is

performed

the

relays

should

be

set

on

the

basis

of

the

middle

or

neutral

tap

position

.

The

total

mismatch

,

includ

-

ing

the

automatic

tap

change

should

not

exceed

15

%

with

a

30

%

sensitivity

relay

,

and

20

%

with

a

35

%

sensitivity

relay

.

Note

from

Figures

13

and

14

that

an

ample

safety

margin

exists

at

these

lev

-

els

of

mismatch

.

g

.

Check

current

transformer

performance

.

Ratio

er

-

ror

should

not

exceed

10

%

with

maximum

symmetrical

external

fault

current

flowing

.

An

ac

-

curate

method

of

determining

ratio

error

is

to

use

ratio

-

correction

-

factor

curves

(

RCF

)

.

A

less

accu

-

rate

,

but

satisfactory

method

is

to

utilize

the

ANSI

t

The

factor

of

3

accounts

for

conditions

existing

during

a

phase

fault

.

Table

1

HU

Relay

Tap

Ratios

TAP

8.7

2.9

5.0

3.2

3.5

3.8

4.2

4.6

3.000

2.9

1.000

1.103

1.586

1.724

1.207

1.310

1.448

3.2

1.563

2.719

1.000

1.094

1.188

1.313

1.438

2.486

3.5

1.000

1.086

1.200

1.314

1.429

2.289

3.8

1.316

1.000

1.105

1.211

2.071

1.190

4.2

1.000

1.095

1.087

1.890

4.6

1.000

1.740

5.0

1.000

1.000

8.7

8

Courtesy of NationalSwitchgear.com

I

.

L

41

-

347.1

S

than

the

lower

polar

unit

.

However

,

if

the

pickup

val

-

ue

is

considered

to

be

too

low

,

it

should

be

checked

after

applying

a

polarizing

current

magnitude

of

20

times

tap

value

to

relay

terminals

3

and

7

.

This

will

cause

the

upper

polar

unit

to

pickup

at

a

current

of

approximately

1.65

amperes

.

7

.

INSTALLATION

The

relays

should

be

mounted

on

switchboard

pan

-

els

or

their

equivalent

in

a

location

free

from

dirt

moisture

,

excessive

vibration

and

heat

.

Mount

the

relay

vertically

by

means

of

the

four

mounting

holes

on

the

flange

for

semi

-

flush

mounting

,

or

by

means

of

the

rear

mounting

stud

or

studs

for

projection

mounting

.

Either

a

mounting

stud

or

the

mounting

screws

may

be

utilized

for

grounding

the

relay

.

The

electrical

connections

may

be

made

directly

to

the

terminals

by

means

of

screws

for

steel

-

panel

mount

-

ing

or

to

the

terminal

studs

furnished

with

the

relay

for

thick

panel

mounting

.

The

terminal

studs

may

be

easily

removed

or

inserted

by

locking

two

nuts

on

the

stud

and

then

turning

the

proper

nut

with

a

wrench

.

For

detailed

FT

case

information

,

refer

to

I

.

L

.

41

-

076

.

8.1

.

2

Indicating

Instantaneous

Trip

Pickup

.

With

switch

open

and

relay

set

on

the

number

5

tap

,

apply

current

specified

in

following

table

to

relay

.

In

-

stantaneous

trip

should

pickup

and

its

target

should

drop

freely

:

HU

/

HU

-

1

HU

-

4

50

amperes

75

amperes

The

contact

gap

should

be

approximately

0.094

inches

between

the

bridging

moving

contact

and

the

adjustable

stationary

contacts

.

The

bridging

moving

contact

should

touch

both

stationary

contacts

simul

-

taneously

.

8

.

ADJUSTMENTS

AND

MAINTENANCE

The

proper

adjustments

for

correct

operation

of

this

relay

have

been

made

at

the

factory

and

should

not

be

disturbed

after

receipt

by

the

customer

.

8.1

.

3

Indicating

Contactor

Switch

(

ICS

)

Block

contacts

of

the

polar

units

closed

.

Pass

suffi

-

cient

direct

current

through

the

trip

circuit

to

close

the

contacts

of

the

ICS

.

This

value

of

current

should

be

not

greater

than

the

particular

tap

setting

being

used

.

The

operation

-

indicator

target

should

drop

freely

.

8.1

Performance

Check

The

following

check

is

recommended

to

verify

that

the

relay

is

in

proper

working

order

.

All

checks

can

best

be

performed

by

connecting

HU

and

HU

-

1

re

-

lays

per

test

circuit

of

Figure

21

and

the

HU

-

4

relay

per

test

circuit

of

Figure

22

.

Relays

must

be

tested

in

the

case

.

8.1

.

4

Differential

Characteristic

a

.

Close

switch

to

position

1

.

Set

lac

to

zero

and

ISR

to

either

28

amperes

for

HU

/

HU

-

1

relays

or

38

amperes

for

HU

-

4

relay

.

Adjust

lac

to

20

amperes

.

Check

the

operating

point

for

the

relay

by

gradu

-

ally

adjusting

ISR

.

Operation

should

occur

between

the

following

limits

:

8.1

.

1

Minimum

Trip

Circuit

.

NOTE

:

The

moving

contact

of

the

upper

polar

unit

(

HRU

)

closes

to

the

left

-

hand

(

front

view

)

stationary

contact

.

The

moving

contact

of

the

lower

polar

unit

(

DU

)

clos

-

es

to

the

right

hand

(

front

view

)

station

-

ary

contact

.

Relay

Type

ILR

lac

With

SPDT

switch

open

and

relay

set

on

5

-

ampere

tap

,

apply

1.35

to

1.65

amperes

for

the

30

%

sensitiv

-

ity

relay

and

1.6

to

1.9

amperes

for

the

35

%

sensitiv

-

ity

relay

.

The

upper

polar

unit

(

HRU

)

should

operate

.

The

upper

polar

unit

may

operate

for

lower

currents

,

but

not

below

1.0

ampere

.

This

low

pickup

will

not

impair

its

operation

on

magnetizing

inrush

currents

and

should

not

be

disturbed

if

it

is

found

to

be

less

45

to

50

amps

.

HU

/

HU

-

1

20

amps

53

to

56

amps

.

HU

-

4

20

amps

.

b

.

For

30

%

Sensitivity

Relays

:

Close

switch

posi

-

tion

1

.

Set

lac

to

zero

and

adjust

ISR

to

either

10

amperes

for

HU

/

HU

-

1

relays

or

6

amperes

for

9

Courtesy of NationalSwitchgear.com

I

.

L

.

41

-

347.1

S

HU

-

4

relays

.

Increase

lac

to

2.8

amperes

.

If

the

lower

polar

unit

does

not

operate

,

lower

IgR

.

The

relay

should

operate

between

the

following

limits

:

9

.

IN

SERVICE

TEST

Refer

to

the

Tables

2

combinations

.

3

,

or

4

for

different

tap

All

relays

should

be

checked

at

least

once

every

year

or

at

such

other

time

intervals

as

may

be

dictat

-

ed

by

experience

to

be

suitable

to

the

particular

application

.

All

contacts

should

be

periodically

cleaned

.

A

con

-

tact

burnisher

style

#

182

A

836

H

01

is

recommended

for

this

purpose

.

The

use

of

abrasive

material

for

cleaning

contacts

is

not

recommended

,

because

of

the

_

danger

of

embedding

small

particles

in

the

face

of

the

soft

silver

and

thus

impairing

the

contact

.

All

checks

can

be

performed

by

connecting

the

relay

per

the

test

circuit

of

Figures

21

or

22

.

Relays

to

be

tested

in

their

case

.

Relay

Type

lac

*

LR

HU

/

HU

-

1

2.8

to

2.95

amps

11.8

to

12.8

amps

HU

-

4

2.8

to

2.95

amps

8.0

to

9.1

amps

c

.

Reverse

leads

to

restraint

transformers

and

re

-

peat

differential

test

outlined

in

paragraphs

a

and

b

.

Results

should

be

approximately

the

same

as

obtained

under

these

paragraphs

.

d

.

For

35

%

Sensitivity

Relays

:

Close

switch

to

po

-

sition

1

.

Set

lac

to

zero

and

adjust

ISR

to

either

9

amperes

for

HU

/

HU

-

1

relays

or

5

amperes

for

HU

-

4

relays

.

Increase

lac

to

2.8

amperes

.

If

the

lower

polar

unit

does

not

operate

lower

ISR

.

The

lower

polar

unit

should

operate

between

the

fol

-

lowing

limits

.

In

the

HU

relay

,

terminal

5

supplies

the

upper

tap

block

and

Terminal

7

supplies

the

lower

tap

block

.

In

the

HU

-

1

,

Terminal

5

supplies

the

first

(

upper

)

tap

block

,

Terminal

7

supplies

the

second

tap

block

and

Terminal

9

supplies

the

lower

tap

block

.

In

the

HU

-

4

,

Terminal

13

supplies

the

first

(

upper

)

tap

block

,

Ter

-

minal

5

supplies

the

second

tap

block

,

Terminal

7

supplies

the

third

tap

block

and

Terminal

9

supplies

the

lower

tap

block

.

ISR

should

be

connected

to

the

Terminal

with

the

lowest

tap

setting

.

Relay

Type

ac

ILR

HU

/

HU

-

1

2.8

to

2.95

amps

10.8

to

11.8

amps

HU

-

4

2.8

to

2.95

amps

7.0

to

7.8

amps

9.1

Minimum

Trip

9.1

.

1

Lower

Unit

(

Differential

)

With

S

.

P

.

D

.

T

.

switch

open

,

the

lower

polar

unit

in

a

30

%

relay

should

operate

with

lac

between

30

%

and

31

%

of

the

setting

of

the

tap

block

corresponding

to

the

terminal

conducting

ILR

.

For

35

%

relays

,

opera

-

tion

should

occur

between

34

%

and

36

%

of

tap

setting

.

e

.

Reverse

leads

to

restraint

transformers

and

re

-

peat

differential

test

outlined

in

paragraphs

a

and

d

.

Results

should

be

approximately

the

same

as

obtained

under

these

paragraphs

.

8.1

.

5

Harmonic

Restraint

Characteristic

Close

switch

to

position

2

.

Short

out

ILR

ammeter

.

Set

ldc

t

°

4

amperes

and

adjust

!

ac

until

upper

polar

unit

operates

.

Iac

should

read

between

6.5

and

9

amperes

.

Upper

Unit

(

Harmonic

Restraint

)

With

S

.

P

.

D

.

T

.

switch

open

,

the

upper

polar

unit

should

operate

with

lac

between

27

%

and

33

%

of

the

setting

of

the

tap

block

corresponding

to

the

terminal

conducting

ILR

.

The

application

of

a

polarizing

cur

-

rent

of

20

times

ILR

tap

value

current

between

Ter

-

minal

3

and

the

terminal

conducting

ILR

,

will

make

9.1

.

2

As

shown

in

Figure

23

,

these

values

of

alternating

current

correspond

to

17

percent

and

14

percent

second

harmonic

.

10

Courtesy of NationalSwitchgear.com