GE STD15C Manuale utente

K-45307K

INSTRUCTIONS

TRANSFORMER

DIFFERENTIAL

RELAYS WITH

PERCENTAGE

AN!)

HARMONIC

RESTRAINT

TYPES

STD15C

and

STD16C

Protection

and

Control

205

Great

Valley

Parkway

Malvern,

19355-1337

GEK-45307

DESCRIPTION

APPLICATION

CALCULATION

SETTINGS

Method

Current

Transformer Connections

Determination

Turns

and

Type

STD

Relay

Tap

Setting

Current Transformer

Ratio

Error

Percent

Slope

Setting

Determination of

Turns

and

STD

Relay

Tap

Setting

Percent

Ratio

Error

Repeat

Turns

and

Relay

Tap

Setting

Repeat

Percent

Ratio

Error

III

Percent

Slope

Setting

RATINGS

Models

12STD15B

and

12STD16B

Auxiliary

Relay

Control

Circuit

CHARACTERISTICS

Pickup

and

Operating

Time

Overcurrent

Unit

Pickup

Percentage

Differential Characteristics

Harmonic

Restraint

Characteristics

BURDENS

CONSTRUCTION

Current

Transformers

Through—Current

Restraint Circuit

Differential-Current

Circuit

Overcurrent

Unit

Main

Operating

Unit

Target

and

Seal-in

Unit

Case

RECEIVING,

HANDLING

AND

STORAGE

ACCEPTANCE

TESTS

Visual

Inspection

Mechanical

Inspection

Electrical

Tests

Test

Equipment

INSTALLATION

PROCEDURE

Tests

Pickup

Harmonic

Current

Restraint

Through-Current

Restraint

Instantaneous

Overcurrent

Unit

Dropout

Main

Unit

Location

Mounting

Connections

ADJUSTMENTS

Tap

Plug

Positioning

Percent

Slope

Setting

OPERATION

Targets

Disabling

Type

STD

Relay

MAINTENANCE

Contact Cleaning

PERIODIC

TESTS

Pickup

Harmonic

Current

Restraint

Through-Current

Restraint

SERVICING

RENEWAL

PARTS

GEK-45

307

TRANSFORMER

DIFFERENTIAL

RELAYS

WITH

PERCENTAGE

AND

HARMONIC

RESTRAINT

STD15C

and

STD16C

INTRODUCTION

Relays

the

STD

type

are

transformer

differential

relays

provided

with

the

features

of percentage

and

harmonic

restraint.

static

decision

unit

controls

small

telephone-type

relay

that

provides

the

contact output.

Percentage

restraint

permits

accurate

discrimination

between

internal

and

external

faults

high

current,

while

harmonic

restraint

enables

the

relay

distinguish,

the

difference

waveform,

between

the

differential

current

caused

internal

fault,

and

that

transformer

magnetizing

inrush.

DES

CR1

PTI

Each Type

STD

relay

single-phase

unit.

The

Type

STD15C

relay

designed

used

for

the

protection

two-winding

power

transformers

and

has

two

through-

current

restraint

circuits

and

one

differential—current

circuit.

The

Type

STD16C

relay

is designed

for

use

with

three—winding

power

transformers

and

has

three

through-current

restraint

circuits

and

one

differential—current

circuit.

may

also

used

for

four-circuit

transformer

protection

(see

Figure

when

only

three

circuits

require

through-current

restraint,

while the

fourth

circuit,

being

the

weakest,

needs

through-current

restraint.

APPLICATION

The

current

transformer

ratios

and

relay

taps

should

selected

obtain

the

maximum

sensitivity

without

risking

thermal

overload

the

relay

current

transformer

(CT),

the

possibility

misoperation.

Therefore,

current

transformer

ratios

the

various

windings

the

power

transformer

should

selected

with the

following

points

mind:

The

lower

the

relay

tap

and

the

lower

the

ratio

selected,

the

higher

will

the

sensitivity.

However,

the

lowest

ratio

and

the

lowest

relay

tap

may

not

compatible

with

some

the

following

restrictions.

Where

choice

available

increasing

either

the

ratio

the

relay

tap,

desirable

increase

the

ratio

preference

the

relay

tap.

Since

the

relay

burden

likely

small

compared

the lead

burden,

increasing

the

ratio

tends

improve

the

relative

performance

the

CT5,

result

reducing

the

maximum

secondary

fault

current

and

increasing

the

accuracy

the

CTs.

These

1nstrucron5

not

purport

cover

i.11

details

variations

equipaent

nez

provide

for

every

possible

ctingency

met

connection

with

installation,

operation

IlntnCe.

Should

further

nforma

ton

desi red

should

parti

cular

probleme

arise

which

are

not

covered

ziWficiently

for

the

purchaser’s

purposes,

the

matter

should

referred

the

General

Electric

Company.

the

extent

required

the

products

described

herein

meet

applicable

ANSI,

IEt

andN

standards,

but

such

assurance

given

with

respect

local

codes

and

ordinances

because

they

varç

greatly.

GEK—45307

The

secondary

current

should not

exceed

the continuous

thermal

rating

the

secondary

winding.

The

relay

current

corresponding

maximum

kVA

(on

forced-cooled

basis)

should

not

exceed

twice

tap

value,

which

the

thermal

rating

the

relay.

The

ratios

should

high

enough

that

the

secondary

currents

will

not

damage

the

relay

under

maximum

internal

fault

conditions

(refer

RATINGS).

The

relay

current

corresponding

rated

kVA

the

power

transformer

(on

self-

cooled

basis)

should

not

exceed

the

relay

tap

value

selected

(magnetizing

inrush

night

operate

the

instantaneous

overcurrent

unit).

the

transformer

under

consideration

does

not

have

self—cooled

rating,

the

transformer

manufacturer

should

consulted for

the

“equivalent

self—cooled

rating”;

that

the

rating

self-cooled

transformer

that

would

have

the

same

magnetizing

inrush

characteristics

the

transformer

being

considered.

The

current

transformer

tap

chosen

must

able

supply

the

relay

with

times

rated

relay

tap

current,

with

error

less

than

20%

the

total

current.

the

current

transformers

produce

error

greater

than

20%

less

than

times

tap

value,

the

harmonic

content

the

secondary

current

may

sufficient

cause

false

restraint

internal

faults.

The

ratios

should

selected

provide

balanced secondary

current

external

faults.

Since

rarely

possible

match

the secondary

currents

exactly

selection

current

transformer

ratios,

ratio—matching

taps

are

provided

the

relay

means

which

the

currents

may

usually

matched

within

5%.

When

the

protected

transformer

equipped

with

load-ratio

control

obvious

that

match

cannot

obtained

all

points

the

ratio-

changing

range.

this

case,

the

secondary

currents

are

matched

the

middle

the

range

and

the

percentage_differential

characteristic

the

relay

relied

upon

prevent

relay

operation

the

unbalanced

current

which

flows

when

the

load-ratio

control

the

ends

the

range.

some

applications,

the

power

transformer

will

connected

the

high

voltage

low

voltage

system

through

four

breakers

(as

shown

Figure

for

example

ring—bus

arrangement.

this

case,

the

ratios

must

selected

that

the

secondary

windings

will

not

thermally

overloaded

load

current

flowing

around

the

ring

addition

the

transformer

load

current.

recommended

that

CTs

each

the

two low

voltage

(or

high

voltage)

breakers

connected

separate

restraining

winding

assure

restraint

heavy

through-fault

current

flowing

around

the

ring

bus.

is not

desirable

protect

two

parallel

transformer

banks

with

one

set

differential

protection,

since

the

sensitivity

the

protection

would

reduced.

addition,

the

banks

can

switched

separately,

there is

possibility

false

operation

magnetizing

inrush

one

transformer

bank,

causing

“sympathetic

inrush”

into

the

bank

already

energized.

this

case,

the

harmonics

tend

flow

between

the

banks,

with the

possibility

that

there

will

insufficient

harmonics

the

relay

current

restrain

the

relay.

Typical

elementary

diagrams

for

the

STD15C

and

STD16C

are

illustrated

Figures

and

GEK—45307

CALCULATION

SETTINGS

METHOD

The

calculations

required

for

determining

the proper

relay

and

taps

are

outlined

below.

sample

calculation,

for

the

transformer

shown

Figure

then

given.

CURRENT

TRANSFORMER

CONNECTIONS

Power

Transformer

Connections

Current

Transformer

Connections

Delta-Wye

Wye-Delta

Wye-Del

Del

ta-Wye

Delta-Delta

Wye—Wye

Wye-Wye

Delta-Delta

Delta-Zigzag

with

phase

Delta—Delta

shift

between

primary

and

secondary

DETERMINATION

TURNS

AND

TYPE

STD

RELAY

TAP

SETTING

Determine

the

maximum

line currents

(Max.

the

basis

that

each

power

transformer

winding

may

carry

the

maximum

forced—cooled

rated

kVA

the

transformer.

—

Maximum

Transformer

kVA

Max.

(Line

kV)

2. Determine

the

full—load

rated

line

currents

(100%

the

basis

that

each

power

transformer

winding

may

carry

the

full

self-cooled

rated

kVA

the

transformer,

the

“equivalent”

self-cooled

ratings.

—

100%

Transformer

kVA

100%

‘P

(Line

kV)

Actually,

this calculation

does

not

mean

that

all

windings

will

necessarily

carry

these

maximum

load

currents

continuously.

This

only

convenient

way

calculating

the

currents

the

other

windings

proportion

their

voltage

ratings.

This

the

requirement

for

selecting

the

relay

tap

setting

that

the

relay

will

not

operate

for

any

external

fault.

Select

ratios

that

the

secondary

current

corresponding

maximum

Ip does

not

exceed

the

secondary

thermal

rating

amperes).

the

case

where

transformer

connected

ring

bus,

for

example,

the

ratio

should

selected

that

the

thermal

rating

will

not

exceeded

the

maximum

load

current

either

breaker.

Also,

select

ratios

that

the

relay

currents

can

properly

matched

means

the

relay taps.

(Highest

current

not

than

times

lowest

current).

For

Wye-connected

CTs

Tap

Current

100%

GEK-45307

For

Delta-connected

CTs

Tap

Current

LnL

where

the

number

secondary

turns.

Check

the

matching

relay

currents

relay

taps,

keep

the

mismatch

error

low

possible.

Calculate

the

percentage

mismatch

follows:

two—winding

transformers,

determine

the

ratio

the

two

relay

currents

and

the

tap

values

selected.

The

differences

between

these

ratios,

divided

the

smaller

ratio,

the

percent

mismatch.

The

mismatch

normally

should

not

exceed

5%.

For

three-winding

transformers,

the

percent of

mismatch

error

should

checked

for

all

combinations

currents

taps.

taps

cannot

selected

keep

this

percentage

error

within

allowable

limits,

will

necessary

choose

different

ratio

one

lines,

obtain

better

match

between

relay

currents

and

relay

taps.

Check

see

that

the

sum

the

relay

currents

that

will

applied

the

relay

for

fault

the

terminals

the

power

transformer

less

than

220

amperes

RMS

for

second.

the

period

during

which

fault

current

flows

the

relay

can

definitely

limited

shorter

time,

higher

current

can

accommodated

accordance

with

the

relation:

(Amperes)?

seconds

48,400

Also

check

that

the

suni

the

multiples

tap

current

internal

external

fault

not

exceed

150.

CURRENT

TRANSFORMER

RATIO

ERROR

The

ratio

error

must

less

than

20%

times

relay

rated

tap

current.

This

based

the

instantaneous

unit

being

set

its

normal

setting,

which

times

tap

rating.

the

instantaneous

unit

pickup

raised

above

this

value,

the

20%

figure

must

reduced,

described

the

CHARACTERISTICS

section.

The

calculations

listed

below

are

for

the

worst—fault

condition,

far

performance

concerned,

which

internal

ground

fault

between

the

and

the

transformer

winding,

with

none

the

fault

current

supplied

through

the

neutral of

the

protected

transformer.

Determine

the

burden

each

CT,

using

the

following

expressions:

For

Wye-connected

CTs

Ne+2f

Ohms

(Equation

For

Delta-connected

CTs

Ohms

(Equation

1000

GEK-45307

where

STD

relay

total

burden

(see

Table

number

turns

bushing

resistance

per

turn,

milliohms

(at

maximum

expected

tempera

ture)

busing

resistance

per

lead,

milliohms

(at

maximum

expected

temperature)

one-way

control

cable

lead

resistance

(at

maximum

expected

temperature)

TABLE

Total

Burden

for

Cycle

Relays

STD

TAPS

AMPS

TAP

AMPS

BURDEN

OHMS

(B)

MIN

P.U.

AMPS

2.9

23.2

0.180 0.87

3.2

25.6

0.156

0.96

3.5

28.0 0.140

1.05

3.8

30.4

0.120

1.14

4.2

33.6

0.112

1.26

4.6

36.8

0.096 1.38

5.0

40.0

0.088

1.50

8.7

69.6

0.048

2.61

Determine

secondary

current

for

times

tap

setting.

STD

relay

tap

rating

(Note:

For

the

location

fault

assumed,

all

the

fault

current

supplied

one

CT,

that

current

and

relay

current

are the

same,

regardless

whether

the

CTs

are

connected

wye

delta.)

Determine

secondary

voltage

required

times

tap

setting.

Esec

From

excitation

curve

particular

tap

current

transformer

being

used,

determine

excitation

current

IE.

corresponding

this

secondary

voltage,

Esec.

Determine

the

percent

error

each

the

expression:

error

100

This

should

not

exceed

20%

any

set

CTs.

does,

will

necessary

choose

higher

tap

that set

CTs,

and

repeat

the

calculations

selection

relay

taps,

mismatch

error,

and

percent

ratio

error.

GE:K-45307

PERCENT

SLOPE

SETTING

The

proper

percent

slope

required

determined

the

sum

of:

The

maximum

range

manual

taps

and

the

load—ratio-control,

automatic

tap

changing

means,

percent.

The

maximum

percent

mismatch

the

relay

taps.

Set

the

desired

percent

slope

means

(See

Figure

6A).

The

percentage

slope

setting

selected

should

greater

than

the

ratio

maximum

total

error

current

the

smaller

the

through

currents.

general,

the

total

error

current

does

not

exceed

20%,

the

25%

setting

used.

exceeds

20%,

but

not

35%,

the

40%

setting

used.

the

movable

lead

used

(as

Figure

for

example)

the

percent

slope

setting

should

chosen

about

twice

high,

since

the

movable

lead

provides

restraint.

EXAMPLE

(REFER

FIGURE

Determination

Turns

and

STD

Relay

Tap

Settings

Transformer

and

Line

Maximum

3750/

(Line

kV)

19.7

49.5

157

100%

3000/

(Line

kV)

15.7

39.6

125

Assume

turns

(N)

20 20

Maximum

secondary

(less

than

5a)

0.98

2.47

2.62

100%

secondary

0.79

1.98

2.08

connections

Delta

Wye

Delta

Relay

Current

for

100%

Sec.

1.37

1.98

3.60

Select

relay

tap for

one

the

line

currents

and

calculate

what

the

currents

other

lines

would

they

were

increased

the

same

ratio.

any

current

greater

than

times

any

other,

the

8.7

tap

should

chosen

for

it,

and

new

ideal

relay

taps

calculated

for

the

other

lines.

Ideal

Relay

Taps

(Set

8.7)

3.31

4.78 8.7

10.

Try

Relay

Taps

3.2

4.6 8.7

11.

Check

Mismatch

Error

Ratio

Taps

Lines

B-A

1.43

Ratio

Sec.

Lines

Currents

1.98

1.37

—

1.44

Mismatch

1.44

0.7%

Ratio

Taps

LinesC-B

-!.j-

1.89

Ratio

Sec.

Line

Currents

1.82

1.89

1.82

Mismatch

3.8%

K—45

307

Ratio

Taps

Lines

C-A

2.72

Ratio

Sec.Line

Currents

2.63

Mismatch

2.72

-2.63

(All

are

less

than

5%;

therefore

mismatch

error

not

excessive)

12.

Check

that

the

sum

of the

maximum

relay

currents

less

than

220

amps

for

second,

and

therefore,

short-time

rating

relay

not

exceeded.

II.

Percent

Ratio

Error

ASSUME

(all

measured

their

maximum

One-way

CONTROL

CABLE

RESISTANCE

Bushing

resistance

per

turn

II II

Bushing

resistance

per

lead

II II

expected

temperatures)

(R)

0.284

ohms

Ce)

rnilliohms

(e)

2.5

Ce)

2.3

(f)

niilliohms

(f)=525

(f)

18.6

Burdens

CTs,

using

Equation

from

page

Line

(0.156)

(20x4)

(2.0

75)

1000

0.312

0.205

0.568

1.085

(.284)

Line

0.096

(20

2.5)

(2.0

52.5)

1000

T.o85

25.6

27.8

.00

3.4%

0.568

0.8

36.8

29.4

136%

0.833

69.6

58.0

0.5

0.8%

Exciting

current

line

too

high;

should

improve

performance.

Repeat

—

Turns

and

Relay

Tap

Setting

try

higher

tap

100%

Try

turns

(necessary

change

also

for proper

matching)

100%

secondary

Relay

Current

Ideal

Relay

Taps

(Set

8.7)

Use

Relay

Taps

Mismatch

Error is

less

than

0.096

0.138

0.568

0.80

Line

(0.048)

(60

2.3)+(2

18.6)

0.568

0.096

0.180

0.568

0.833

Impedance,

ohms

times

tap,

amperes

voltage

require

(IZ)

required,

from

excitation

curve

Ratio

Error

15.7 39.6

125

40 80

0.79 0.99

1.56

1.37

0.99

2.70

4.40

3.19

8.7

4.6

3.2 8.7

GEK-45307

Repeat

Percent

Ratio

Error

Burden

CTs

Line

0.192

0.205

0.568

0.965

Line

0.156

0.188

0.568

0.912

Line

0.096

0.226

0.568

0.890

Impedance

Ohms

0.965

0.912

0.890

times

Tap,

Amperes

36.8 25.6 69.6

voltage

required

(17)

35.6 23.4

61.9

‘C

required,

from

excitation

curve

1.1 0.25

0.17

Ratio

Error

3.1%

1.0%

0.3%

Percent

error

less

than

20%,

taps

and

relay

taps

are

satisfactory.

III

Percent

Slope

Setting

Assume

load

ratio

control

maximum

range

10.0%

Relay

tap

mismatch,

from

above

(Lines

A-B)

4.6%

Use

25%

setting

14.6%

RATI

NGS

MODELS

12STD15C

AND

12STD16C

Continuous

Rating

The

through-current

transformer

and

differential-current

transformer

will

stand

twice

tap value

for

any

combination

taps,

or they

will

stand

twice

tap

value

all

but

one

the

restraint

windings

carry

current,

and

the

full

restraint

current

(equal

twice

tap value)

flows

through

the

differential—current

transformer.

Short

Time

Rating

(Thermal)

220

amperes

for

second,

measured

the primary

any

transformer

the

type

STD

relay.

Higher

currents

may

applied

for

shorter

lengths

time

accordance

with

the

following

equation:

48,400

where

current

amperes

time

seconds.

Short

Time

(Electrical

For

both

the

STD15C

and

STD16C

the

sum

the

multiples

tap

current

fed

the

relay

from

the

several

sets

current

transformers

should not

exceed

150.

These

multiples

should

calculated

the

basis of

RMS

symmetrical

fault

current.

This

limitation

result

the

voltage

rating

the

rectifiers

the

through—

current

restraint

circuit.

Note

that

Figure

external

fault

current

can

flow

through

circuit

breakers

52—1

and

52—2

without

being

limited

the

transformer

peda

ce.

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