CHAPTER 4

PROTECTION REQUIREMENTS

4.1

CHAPTER 4

PROTECTION REQUIREMENTS

4.1 General Means of protection for automatic disconnection against phase and earth faults

shall be provided on the customer main switch. The type and settings of protective devices shall be so selected that they can grade properly with HK Electric infeed protection.

The customer shall provide Time-Current curve showing that the proposed

protection scheme for the main switch can grade properly with HK Electric system under both phase fault and earth fault conditions.

4.2 Customer HV Main Switch 1. Anticipated maximum 11-kV fault level:- Phase fault: 18.4 kA (350 MVA) Earth fault: 2.0 kA

To grade with HK Electric 11-kV feeder protection, the protective relays of customer 11-kV main switch shall have an operating time not exceeding the maximum allowable time-current curves for phase fault and earth fault as shown in Drg. Nos. GCS/4/01 and 02 respectively.

2. Anticipated maximum 22-kV fault level:-

Phase fault: 25 kA (952 MVA) Earth fault: 2.5 kA

To grade with HK Electric 22-kV feeder protection, the protective relays of customer 22-kV main switch shall have an operating time not exceeding the maximum allowable time-current curves for phase fault and earth fault as shown in Drg. Nos. GCS/4/03 and 04 respectively.

3. Protection C.T.s shall have adequate output to prevent C.T. saturation.

The customer shall provide document/calculation sheet to show that the proposed C.T.s have adequate output for the application under both phase and earth fault conditions.

4.2

4.3 Customer LV Main Switch 1. The anticipated maximum LV (380 V) fault level is 40 kA (26 MVA). The

overcurrent protection of customer LV main switch shall grade with HK Electric's transformer overcurrent protection and has an operating time not exceeding the maximum allowable time-current curves for various ratings of LV main switches as shown in Drg. No. GCS/4/05.

2. The customer protective devices shall be set so that disconnection is

achieved within 5 seconds during an earth fault. 3. Bonding Between HK Electric and Customer's Earthing Systems a. Under the current regulations, the customer's earthing system shall

be bonded to that of the HK Electric’s earthing system for transformer supplies. This will cause a significant increase in LV earth fault current, the magnitude of which can be as high as phase fault current.

b. If the customer LV overcurrent and earth fault protections share the

same set of C.T.s, high output C.T.s and low burden type earth fault relay shall be used to prevent C.T. saturation. The customer shall provide document/calculation sheet to show that the proposed protection C.T.s have adequate output for the application under earth fault condition.

c. As an alternative to the use of high output C.T.s and low burden type

earth fault relay, separate sets of C.T.s can be used for overcurrent and earth fault protections as shown in Drg. No. GCS/4/06.

4.4 Protection Scheme For Main Switch The customer is advised to provide a summary sheet as shown in Drg. No.

GCS/4/07 and GCS/4/08 for LV and HV main switch protection scheme respectively to HK Electric for consideration.

4.5 Auxiliary Supply for Protection Scheme and Relay If the customer protection scheme or relay requires an auxiliary supply, the

auxiliary supply shall be reliable and not be interrupted during LV or HV faults on the customer equipment to ensure that the customer protection scheme and relay perform the protection function properly.

4.3

4.6 Schedule of Drawings - Protection Requirements Drawing No. Drawing Title GCS/4/01 Maximum Allowable Time-Current Curve of

Overcurrent Protection at Customer 11-kV Main Switch

GCS/4/02 Maximum Allowable Time-Current Curve of Earth

Fault Protection at Customer 11-kV Main Switch GCS/4/03 Maximum Allowable Time-Current Curve of

Overcurrent Protection at Customer 22-kV Main Switch

GCS/4/04 Maximum Allowable Time-Current Curve of Earth

Fault Protection at Customer 22-kV Main Switch GCS/4/05 Maximum Allowable Time-Current Curves of

Overcurrent Protection at Customer LV Main Switch GCS/4/06 Recommended C.T. Arrangement for Customer's

Protective Device at LV Main Switch GCS/4/07 LV Main Switch Protection Scheme Summary Sheet GCS/4/08 HV Main Switch Protection Scheme Summary Sheet

80000

60000

40000

20000

200

400

600

800

2000

4000

6000

8000

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3 0.2

9.0

8.0

7.0

6.0

5.0

4.0 3.0

2.0 0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

1.0

10.0

100

1000

10000

100000

0.1

1.0

10.0

Drg

. No.

GC

S/4/

01M

AX

IMU

M A

LLO

WA

BLE

TIM

E-C

UR

REN

T C

UR

VE

OF

OV

ERC

UR

REN

T PR

OTE

CTI

ON

AT

CU

STO

MER

11-

kV M

AIN

SW

ITC

H

4.4

8000

6000

4000

2000

200

400

600

800

20

40

60

80

9.0

8.0

7.0

6.0

5.0

4.0 3.0

2.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

9.0

8.0

7.0

6.0

5.0

4.0

3.0

2.0 0.9

0.8

0.7

0.6

0.5

0.4 0.3

0.2

0.1

1.0

10.0

10

100

1000

10000

0.1

1.0

10.0

Drg

. No.

GC

S/4/

02M

AX

IMU

M A

LLO

WA

BLE

TIM

E-C

UR

REN

T C

UR

VE

OF

EAR

TH F

AU

LT P

RO

TEC

TIO

NA

T C

UST

OM

ER 1

1-kV

MA

IN S

WIT

CH

4.5

8000

6000

4000

2000

800

600

400

200

20000

40000

60000

80000

0.2

0.3

0.40.5

0.6

0.7

0.80.9

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.2

0.3

0.40.5

0.6

0.7

0.8

0.92.0

3.0

4.0

5.0

6.0

7.08.0

9.0

0.1

1.0

10.0

100

1000

10000

100000

0.1

1.0

10.0

Drg

. No.

GC

S/4/

03M

AX

IMU

M A

LLO

WA

BLE

TIM

E-C

UR

REN

T C

UR

VE

OF

OV

ERC

UR

REN

T PR

OTE

CTI

ON

AT

CU

STO

MER

22-

kV M

AIN

SW

ITC

H

4.6

800

600

400

200

2000

4000

6000

8000

20

40

60

80

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.2

0.3

0.40.5

0.6

0.7

0.8

0.92.0

3.0

4.0

5.0

6.0

7.08.0

9.0

0.1

1.0

10.0

10

100

1000

10000

0.1

1.0

10.0

Drg

. No.

GC

S/4/

04M

AX

IMU

M A

LLO

WA

BLE

TIM

E-C

UR

REN

T C

UR

VE

OF

EAR

TH F

AU

LT P

RO

TEC

TIO

N A

T C

UST

OM

ER 2

2-kV

MA

IN S

WIT

CH

4.7

8000

6000

4000

2000

20000

40000

60000

80000

0.2

0.3

0.40.5

0.6

0.7

0.8

0.9

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.92.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.09

0.08

0.05

0.04

0.06

0.07

0.03

0.02

0.03

0.02

0.04

0.06

0.08

0.09

0.05

0.07

0.01

0.10

1.00

10.0

0

1000

10000

100000

0.01

0.10

1.00

10.0

0

Drg

. No.

GC

S/4/

05M

AX

IMU

M A

LLO

WA

BLE

TIM

E-C

UR

REN

T C

UR

VES

OF

OV

ERC

UR

REN

T P

RO

TEC

TIO

NA

T C

UST

OM

ER L

V M

AIN

SW

ITC

H

4.8

Drg

. No.

GC

S/4/

06R

ECO

MM

END

ED C

.T. A

RR

AN

GEM

ENT

FOR

CU

STO

MER

'S P

RO

TEC

TIV

E D

EVIC

E A

T LV

MA

IN S

WIT

CH

4.9

1. C

ircu

it B

reak

er I

nfor

mat

ion

: (M

ain

Sw

itch

No.

:

)

Mai

n S

wit

ch R

atin

g A

ny B

uilt

-in

Pro

tect

ive

Dev

ice

?In

stan

tane

ous

Tri

p C

urre

nt S

ettin

g (k

A)

and

Max

. Set

ting

Err

or

Set

ting

Det

ails

Yes

No

2.

Cur

rent

Tra

nsfo

rmer

: F

unct

ion

Mak

e M

odel

N

umbe

rR

atio

VA

and

Cla

ssA

ny C

.T. M

agne

tisat

ion

Cur

ve P

rovi

ded

to H

K E

lect

ric

?C

.T. R

esis

tanc

e (o

hm)

Con

nect

ion

Lea

d R

esis

tanc

e (o

hm)

Ove

rcur

rent

P

rote

ctio

n C

.T.

Y

es

No,

to b

e su

bmit

ted

late

r E

arth

Fau

lt P

rote

ctio

n C

.T.

Y

es

No,

to b

e su

bmit

ted

late

r

Wil

l the

ove

rcur

rent

pro

tect

ion

and

eart

h fa

ult p

rote

ctio

n sh

are

the

sam

e se

t of

C.T

.s ?

Y

es

No

3. R

elay

Inf

orm

atio

n :

Fun

ctio

n M

ake

Mod

el

Num

ber

Rat

ed

Cur

rent

(A)

Bur

den

at

Rat

ed C

urre

nt

(VA

)

Aux

ilia

ry S

uppl

y#

(A.C

., D

.C. o

r

N.A

.)

* C

hara

cter

isti

cs e

.g.

EI,

VI,

NI

(1.3

s),

NI

(3 s

)

Plu

g S

ettin

g

Ran

ge

Plu

g

Set

ting

Tim

e M

ulti

plie

r

Set

ting

Rel

ay I

mpe

danc

e

at P

lug

Set

ting

(ohm

)

Ove

rcur

rent

Rel

ay

Ear

th F

ault

Rel

ay

(*

: E

I =

Ext

rem

ely

Inve

rse,

VI

= V

ery

Inve

rse,

NI=

Nor

mal

Inv

erse

) # If

the

cust

omer

pro

tect

ion

sche

me

or r

elay

req

uire

s an

aux

ilia

ry s

uppl

y, th

e au

xili

ary

supp

ly s

hall

be

reli

able

and

not

be

inte

rrup

ted

duri

ng L

V o

r H

V f

aults

on

the

cust

omer

eq

uipm

ent t

o en

sure

that

the

cust

omer

pro

tect

ion

sche

me

and

rela

y pe

rfor

m th

e pr

otec

tion

func

tion

prop

erly

.

4. M

axim

um E

arth

Fau

lt L

oop

Impe

danc

e, if

ava

ilabl

e at

the

time

of s

ubm

issi

on :

____

____

__ o

hm

Not

es :

Fo

llow

ing

info

rmat

ion

shal

l be

prov

ided

:

1.

Cat

alog

ues

for

mai

n sw

itch

(w

ith

deta

ils

of b

uilt

-in

prot

ecti

ve d

evic

e, if

any

), C

.T.s

(in

clud

ing

C.T

. mag

neti

sati

on c

urve

) an

d re

lays

.

2.

A.C

. con

nect

ion

diag

ram

of

over

curr

ent a

nd e

arth

fau

lt p

rote

ctio

n fo

r th

e m

ain

swit

ch.

3. C

alcu

lati

on s

heet

sho

win

g th

at th

e pr

opos

ed C

.T.s

hav

e ad

equa

te o

utpu

t for

the

appl

icat

ion

unde

r bo

th p

hase

and

ear

th f

ault

con

diti

ons.

4.

Tim

e-cu

rren

t cha

ract

eris

tic

curv

e of

ove

rcur

rent

pro

tect

ion

at th

e pr

opos

ed s

etti

ngs

plot

ted

at th

e D

rg. N

o. G

CS

/4/0

5.

D

rg. N

o. G

CS

/4/0

7 L

V M

AIN

SW

ITC

H P

RO

TE

CT

ION

SC

HE

ME

SU

MM

AR

Y S

HE

ET

4.10

1. C

ircu

it B

reak

er I

nfor

mat

ion

: (M

ain

Sw

itch

No.

:

)

Mai

n S

wit

ch R

atin

g A

ny B

uilt

-in

Pro

tect

ive

Dev

ice

?In

stan

tane

ous

Tri

p C

urre

nt S

ettin

g (k

A)

and

Max

. Set

ting

Err

or

Set

ting

Det

ails

Yes

No

2.

Cur

rent

Tra

nsfo

rmer

: F

unct

ion

Mak

e M

odel

N

umbe

rR

atio

VA

and

Cla

ssA

ny C

.T. M

agne

tisat

ion

Cur

ve P

rovi

ded

to H

K E

lect

ric

?C

.T. R

esis

tanc

e (o

hm)

Con

nect

ion

Lea

d R

esis

tanc

e (o

hm)

Ove

rcur

rent

P

rote

ctio

n C

.T.

Y

es

No,

to b

e su

bmit

ted

late

r E

arth

Fau

lt P

rote

ctio

n C

.T.

Y

es

No,

to b

e su

bmit

ted

late

r

Wil

l the

ove

rcur

rent

pro

tect

ion

and

eart

h fa

ult p

rote

ctio

n sh

are

the

sam

e se

t of

C.T

.s ?

Y

es

No

3. R

elay

Inf

orm

atio

n :

Fun

ctio

n M

ake

Mod

el

Num

ber

Rat

ed

Cur

rent

(A)

Bur

den

at

Rat

ed C

urre

nt

(VA

)

Aux

ilia

ry S

uppl

y#

(A.C

., D

.C. o

r

N.A

.)

* C

hara

cter

isti

cs e

.g.

EI,

VI,

NI

(1.3

s),

NI

(3 s

)

Plu

g S

ettin

g

Ran

ge

Plu

g

Set

ting

Tim

e M

ulti

plie

r

Set

ting

Rel

ay I

mpe

danc

e

at P

lug

Set

ting

(ohm

)

Ove

rcur

rent

Rel

ay

Ear

th F

ault

Rel

ay

(*

: E

I =

Ext

rem

ely

Inve

rse,

VI

= V

ery

Inve

rse,

NI=

Nor

mal

Inv

erse

) # If

the

cust

omer

pro

tect

ion

sche

me

or r

elay

req

uire

s an

aux

ilia

ry s

uppl

y, th

e au

xili

ary

supp

ly s

hall

be

reli

able

and

not

be

inte

rrup

ted

duri

ng L

V o

r H

V f

aults

on

the

cust

omer

eq

uipm

ent t

o en

sure

that

the

cust

omer

pro

tect

ion

sche

me

and

rela

y pe

rfor

m th

e pr

otec

tion

func

tion

prop

erly

. N

otes

:

Foll

owin

g in

form

atio

n sh

all b

e pr

ovid

ed :

1.

C

atal

ogue

s fo

r m

ain

swit

ch (

wit

h de

tail

s of

bui

lt-i

n pr

otec

tive

dev

ice,

if a

ny),

C.T

.s (

incl

udin

g C

.T. m

agne

tisa

tion

cur

ve)

and

rela

ys.

2.

A.C

. con

nect

ion

diag

ram

of

over

curr

ent a

nd e

arth

fau

lt p

rote

ctio

n fo

r th

e m

ain

swit

ch.

3.

Cal

cula

tion

she

et s

how

ing

that

the

prop

osed

C.T

.s h

ave

adeq

uate

out

put f

or th

e ap

plic

atio

n un

der

both

pha

se a

nd e

arth

fau

lt c

ondi

tion

s.

4.

Tim

e-cu

rren

t cha

ract

eris

tic

curv

es o

f ov

ercu

rren

t pro

tect

ion

and

eart

h fa

ult p

rote

ctio

n at

the

prop

osed

set

ting

s pl

otte

d at

the

Drg

. No.

GC

S/4/

01 &

GC

S/4

/02

(for

11-

kV m

ain

swit

ch)

or D

rg. N

o. G

CS/

4/03

& G

CS

/4/0

4 (f

or 2

2-kV

mai

n sw

itch

) re

spec

tive

ly.

Drg

. No.

GC

S/4

/08

HV

MA

IN S

WIT

CH

PR

OT

EC

TIO

N S

CH

EM

E S

UM

MA

RY

SH

EE

T

4.11