CT-Sizing

PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235

DOC. NO. CU-47000-0202 REV. 01

A.1

CT sizi sizing ng calc calcul ulat atio ion n for for 400k 400kV V Exi Exist stin ing g Bus Bus-B -Bar ar Prot Protec ecti tion on

A.1.1

Ap pl plicable CT CT an an d core Nu Numb er ers: Feeder Detail 400kV

A.1.2

A.1.3

A.1.4 .1.4

CT Ratio

CT No

2000/1

400-6-CT 400-7-CT

Core

Ref. Drawing No.

1

765/400kV Unnao substation SLD:CU-470000001,Rev.00

System Parameter (As per Specification,Vol-II General Technical Requirement 071806-47ES-0200 Rev.0 Cl.6.1) Variable

Value

Unit

Vn

420

kV

Nominal Voltage

Ispec

40

kA

Primary Short Circuit Current

t

1

s

f n

50

Hz

X/R

30

-

Description

Maximum duration of short circuit current System supply Frequency X/R ratio of system

CT Parameter (As (As per Specification ,Vol-III Instrument Transformer 071806-47ES-7230 Rev.0.Cl.2.11.2) Rev.0.Cl.2.11.2) IPN

2000

A

ISN

1

A

Rated Secondary Current

RCT

5

W

CT Resistance at 75 C

Rated Primary Current

o

Rela Relay y Par Param amet eter er (As (As per per the the atta attach ched ed Annex nnexur ure e 1) 1) IR

1

A

Sr

10

VA

Maximum Protective relay Burden(Burden & CT requirement of RA DSS relays)

tm

15

ms

Busbar Protection Relay Operating time(As per Annexure-I)

tCB

40

ms

Circuit Breaker Operating time(As per Annexure-I)

Rated Input Current of Relay used

Page 1

PROJECT: 765kV UNNAO SUBSTATION SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235

A.1.5

Secondary Le Lead Pa Parameter IL

100

m

AL

6

mm2

1

-

3.746

W/km

r L

A.1.6

DOC. NO. CU-47000-0202 REV. 01

Single way length of leads Cross sectional area of leads No of runs of cable connected to CT secondary o

AC resistance of 6 Sq.mm Cu, lead lead at 75 C

Details of of Re Relay Pr Proposed

1

Re R elay Type

:

2

Rated Current,IR

: 1A

Bus Diffrential Diffrential Protection (ABB-RADSS)

3

Short time current carrying capacity,Ith (relay)

:

100 X IR for 1s

= 100 X 1 A for for 1s = 100A

4

Maximum relay input current during through fault, If

=

for 1sec

IPSC/IPN X ISN = 40000/2 40000/2000 000 X 1 = 20.0 20.00A 0A

A.1.7 .1.7

<100A [Ith(relay)]

For Formula and and Requ equirem iremen entts-M s-Meter eterin ing g The following formulae and requirements are applied

1

Rated Symmetrical Short Circuit Current factor(K ssc) KSSC

As per IEC 44-6(Cl.3.15) 44-6(Cl.3.15) = IPSC/IPN = 40 X 1000/20 1000/2000 00 = 20.0 20.00 0

Standard Value of KSSC

2

= 20 20

As per IEC 44-6(Cl.4.1)

Primary Time Constant(TP) For the System Close in Fault

X/R= 30 30 L/R= 30/(2X3.1 30/(2X3.14X50 4X50))

Page 2

PROJECT: 765kV UNNAO SUBSTATION SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235

A.1.5

Secondary Le Lead Pa Parameter IL

100

m

AL

6

mm2

1

-

3.746

W/km

r L

A.1.6

DOC. NO. CU-47000-0202 REV. 01


AC resistance of 6 Sq.mm Cu, lead lead at 75 C

Details of of Re Relay Pr Proposed

1

Re R elay Type

:

2

Rated Current,IR

: 1A

Bus Diffrential Diffrential Protection (ABB-RADSS)

3

Short time current carrying capacity,Ith (relay)

:

100 X IR for 1s

= 100 X 1 A for for 1s = 100A

4

Maximum relay input current during through fault, If

=

for 1sec

IPSC/IPN X ISN = 40000/2 40000/2000 000 X 1 = 20.0 20.00A 0A

A.1.7 .1.7

<100A [Ith(relay)]

For Formula and and Requ equirem iremen entts-M s-Meter eterin ing g The following formulae and requirements are applied

1

Rated Symmetrical Short Circuit Current factor(K ssc) KSSC

As per IEC 44-6(Cl.3.15) 44-6(Cl.3.15) = IPSC/IPN = 40 X 1000/20 1000/2000 00 = 20.0 20.00 0


2

= 20 20


Primary Time Constant(TP) For the System Close in Fault

X/R= 30 30 L/R= 30/(2X3.1 30/(2X3.14X50 4X50))

Page 2


DOC. NO. CU-47000-0202 REV. 01

Therefore Primary Time Constant(T P) at system fault

=

0.096sec = 95.5 95.54m 4msec sec

Standard Value of T P

3

= 120


Duty Cycle(C-O) Single Energisation

= C-t' C-t'-O -O

where t' = Duration of first first current flow t'= tm+tCB = 55ms Sele Select cted ed Duty Duty Cycl Cycle e

4

=

Say 80 mSec

C-80 C-80ms ms-O -O

Resistive Burden(External Burden) RI = (2.IL.r L /1000)

Two way lead resistance

( IL=100 Mtr Longest distance of CT cabling as per Layout) = (2X100X3. (2X100X3.746/10 746/1000) 00) =

2

Rr = Sr/I Sr/Ir r

Relay burden on CT

= 10/1 10/1^^2 =

Rb = RI+R RI+Rr r = 10.75W

Page 3

Considered uniform for CT


DOC. NO. CU-47000-0202 REV. 01

Standard Value of Rb

5

=

Knee Point Voltage

Vk>= 0.5 x If x (RCT+RI)

>= 0.5*20*(5+0.75) >= 57.49 V

8

Rated Equivalent Rated Secondary e.m.f

Eal

= Kssc x Ktd x (RCT + Rb) x ISN

Ktd = Ktf = 2 x pi x f x TP x ( 1 - e

(-t'/TP)

)+1

2 x 3.14 x 50 x (0.12) x (1-e(-0.08/0.12)) + 1

Ktd = Ktf = 19.334

Eal

= Kssc X Ktd X (Rct + Rb) X Isn

Eal

= 6863.73 V

20 x 1.019x (5 + 12.75) x 1

As Equivalent Rated Secondary e.m.f is greater than Knee Point Voltage, CT is capable of supplying Eal to the relay circuit.

A.1.8

Results

t a t n e r r u C y r a m i r P ) N P d I e ( t p a a R T

y r a d n ) o N c S e I t S ( d n e e r t r a u R C

) n f ( y c n e u q e r F d e t a R

(A)

(A)

2000

1

) h t I e ( t m n i T e r r t r u o h C l S a d m e r t e a h R T

e ) m i h T t I t t r ( o n h e r S r f u o C l n o a i t m r a r e u h D T

(Hz)

(kA)

(sec)

(kA)

50

40kA

1

100

c i ) m a n y n d y I t D ( d n e e r t r a u R C

Page 4

r o t t r c a o F h t S n l e a r c r i r u t e C t i m u c m r y i S C

t n a t s n o C e m i T y r a m i r P

(-)

(-)

(ms)

(-)

TPX

20

120

C-80ms-O

C E I r e p s a s s a l C

e l c y C y t u d d e i f i c e p S

n e d r u B e v i t s i s e R

f . m . e . c e S g n i t i m i L . i u q E

(W)

(V)

12.8W

6864V

PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B

DOC. NO. CU-47000-0202 REV. 01

B.1

CT sizing calculation for 400kV Transformer Differential Protection(87TA)-Low Impedace Protection

B.1.1

Applicable CT and core Numbers:

B.1.2

B.1.3

B.1.4

B.1.5

Feeder Detail

CT Ratio

CT No

Core No.

ICT-1

1600/1

400-6-CTT

2

ICT-2

1600/1

400-7-CTT

2

Ref. Drawing No. 765/400kV Unnao substation SLD:CU-47000-0001,Rev.00


Value

Unit

Vn

420

kV

Nominal Voltage

Description

Ispec

40

kA


t

1

s

f n

50

Hz

X/R

30

-


CT Parameter (As per Specification ,Vol-III Instrument Transformer 071806-47ES-7230 Rev.0.Cl.2.11.2) IPN

1600

A


ISN

1

A


RCT

5

W



o

Relay Parameter (As per the attached Annexure 1) IR

1

A

Sr

0.1

VA

Maximum Protective relay Burden(Burden & CT requirement of Micom r elays)

tm

30

ms

Transformer Differential Relay Operating time(As per Annexure-I)

IS

0.02

A

Minimum Setting of Relay

tCB

40

ms


Single way length of leads

Secondary Lead Parameter IL

350

m

AL

6

mm2

1

-

r L

3.746

W/ km

Cross sectional area of leads No of runs of cable connected to CT secondary o

AC resistance of 6 Sq.mm Cu, lead at 75 C

Page 5

PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B B.1.6

B.1.7

DOC. NO. CU-47000-0202 REV. 01

Transformer Parameter --

1000

MVA

VP

765

kV

Transformer MVA Rating Primary Voltage Rating

VS

400

kV

Secondary Voltage Rating

--

14

%

Percentage Impedance(As per T /Specification,Vol-III 017806-47ES-7130 Rev.o Cl.2.8.1,page 3 & GTP)

Details of Relay Proposed

1

Relay Type

: Transformer differential, Micom P633

2

Rated Current,I R

: 1A

3

Short time current carrying capacity,I th (relay)

: 100 X IR for 1s = 100 X 1 A for 1s = 100A

4

Maximum relay input current during through fault, I f:

for 1sec Source feed considered from 765 KV side and fault current taken as per calculations at Sl. No.1.8 (b) below

IPSC/IPN X ISN = 10310/1600 X 1 <100A [Ith(relay)]

= 6.44A

5

Full load Current,I L

= MVA/(-/3 x VP) = 1000 X 1000/1.732 X 400 = 1443A

B.1.8 1

Through Fault Current Through Fault MVA of Transformer

: MVA Rating/% Impedance = 1000 X 100/14 = 7142.86MVA

2

Through Fault Current on Secondary side of Transformer I PSC(MV):

Fault-MVA/(-/3 XVP) = 7142.86/(1.732*400) = 10.31kA

Page 6

PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B B.1.9

DOC. NO. CU-47000-0202 REV. 01

Formula and Requirements The following formulae and requirements are applied

1

Rated Symmetrical Short Circuit Current factor(K ssc)


KSSC

= Ispec/IPN = 40 X 1000/1600 = 25.00


2

= 25


Primary Time Constant(T P) For the System Close in Fault

X/R= 30 L/R= 30/(2X3.14X50)

Therefore, Primary Time Constant(T P) at system fault

=

0.096sec = 95.54msec


3

= 120



= C-t'-O

where t' = Duration of first current flow t'= tm + tCB = 70ms Selected Duty Cycle

4

=

(say 80 ms)

C-80ms-O



( IL=350 Mtr Longest distance of CT cabling as per Layout) = (2*350*3.746/1000) = 2.62W

2

Rr = Sr/Ir

Relay burden on CT

= 0.1/1^2 = 0.10W

Page 7


DOC. NO. CU-47000-0202 REV. 01 Rb = RI+Rr = 2.722W


5

= 5.00W

Knee Point Voltage

Condition 1

Vk>= K X (RCT+RI)

Applicable If x (X/R)

Condition 2


<= 500 x I SN

6.44 X 30

<= 500 X 1

193.3125

<= 500

Not Applicable 500 x ISN

< If x (X/R)

<

1200

500 X 1

< 25 X 30

<

1200

< 193.3125

<

1200

500

As Condition 2 is satisfied K, K= 0.14 x I f x (X/R) 0.14 X 6.44 X 30 = 27.06

Vk>= K x (RCT+RI) >= 27.06*(5+2.62) >= 206.26V

Vk = 250.00V

6


Eal


Ktd = Ktf = 2 x pi x f x T P x ( 1 - e

(-t'/TP)

)+1

2*3.14*50*(0.12)*(1-EXP(-0.08/0.12))+1

Page 8


DOC. NO. CU-47000-0202 REV. 01 Ktd = Ktf = 19.33

Eal


Eal

= 4833.61V

25*19.33*(5+5)*1

As Equivalent Rated Secondary e.m.f is greater than Knee Point Voltage, CT is capable of supplying Eal to the relay circuit. B.2.10 Results y r a t m i r a ) P t N P d n I r ( e e t r p a u a R C T

(A) 1600

a ( d t n d n o e r e c t r a e u R S C

) n f ( y c n e d u e q t e a r R F

l a t ) r m h o r t h e I ( h S t T n d r e e e t r m u a i R T C

f e ) h o t m l I ( n i o T a t n i t t m r a o r e r r e r u h h u D S T C

c i ) m a n y n d y I ( t D d n r e e t r a u R C

r e p s a s s a C l E C I

r o l i t t a u c c c a i r r F t i e C t n t m r e r m o r y h u S S C

e m i T t y n r a a t s m n i r o P C

y t u d d e i f i e c l e c p y S C

(A) 1

(Hz) 50

(kA) 40kA

(sec) 1

(kA) 100

(-) TPX

(-) 25

(ms) 120

(-) C-80ms-O

)

N y S r I

Page 9

e v n i t s e i s d r e u R B

(W) 5W

f . g m . n e i . t . i i u c m e q i E L S (V) 4834V


DOC. NO. CU-47000-0202 REV. 01

B.2

CT sizing calculation for 400kV Transformer Differential Protection(87TB)-Low Impedace Protection

B.2.1


B.2.2

B.2.3

B.2.4

B.2.5

Feeder Detail

CT Ratio

CT No

Core

ICT-1

1600/1

400-6-CT

4

ICT-2

1600/1

400-7-CT

4



Value

Unit

Vn

420

kV

Nominal Voltage

Description

Ispec

40

kA


t

1

s

f n

50

Hz

X/R

30

-



1600

A


ISN

1

A


RCT

5

W


Rated Input Current of BCU used

o


1

A

Sr

0.2

VA

Maximum Protective relay Burden(Burden & CT r equirement of Micom relays)

tm

30

ms


IS

0.02

-


tCB

40

ms


IL

100

m


AL

6

mm2

1

-

3.746

W/ km

Secondary Lead Parameter

r L

Cross sectional area of leads No of runs of cable connected to CT secondary o


Page 10


B.2.6

B.2.7

DOC. NO. CU-47000-0202 REV. 01


1000

MVA

VP

765

kV


VS

400

kV


--

14

%

Percentage Impedance(As per T/Specificati on,Vol-III 017806-47ES-7130 Rev.o Cl.2.8.1,page 3 & GTP)


1

Relay Type

: Transformer differential, MicomP643

2

Rated Current,I R

: 1A

3

Short time current carrying capacity,I th (relay)

: 100 X IR for 1s = 100 X 1 A for 1s = 100A

4

Maximum relay input current during through fault, I f:

for 1sec Source feed considered from 765 KV side and fault current taken as per calculations at Sl. No.1.8 (b) below

IPSC/IPN X ISN = 10310/1600 X 1 = 6.44A

5


<100A [Ith(relay)]

= MVA/(-/3 x V P) = 1000 X 1000/1.732 X 400 = 1443A

B.2.8 1



2

roug au urren on econ ary s e o Transformer I PSC(MV):

= Fault-MVA/(-/3 XVP) = 7142.86/(1.732*400) = 10.31kA

Page 11


B.2.9

DOC. NO. CU-47000-0202 REV. 01

Formula and Requirements-Metering

The following formulae and requirements are applied 1


Rated Symmetrical Short Circuit Current factor(K sec)

KSSC

= Ispec/IPN = 40 X 1000/1600 = 25.00


2

= 25

Primary Time Constant(T P)

For the System Close in Fault

X/R= 30 L/R= 30/(2X3.14X50)

Therefore Primary Time Constant(TP) at system fault

=

0.096sec = 95.54msec


3

= 120

Duty Cycle(C-O)

= C-t'-O

Single Energisation

where t' = Duration of first current flow t'= tm + tCB = 70ms Selected Duty Cycle

4

=

(say 80 ms)

C-80ms-O



( IL=100 Mtr Longest distance of CT cabling as per Layout) = (2X100X3.746/1000) =

2

Rr = Sr/Ir

Relay burden on CT

= 0.2/1^2 =

Page 12


DOC. NO. CU-47000-0202 REV. 01

Rb = RI+Rr = 0.949W


5

=

Knee Point Voltage


Vk>= K X (RCT+RI)

Condition 1 If <= 5 <= X/R < 40

K = 0.04 x If x (X/R+24.25) + 0.06 x (X/R+177)

Condition 2 If <= 5, 40 <= X/R < 120

K = 12 x If +16

Condition 3 5 < If <= 10, 5<= X/R < 40

K = 0.14 x If x (-X/R-15) + 0.44 x (X/R+202.5)

Condition 4 5 < If <= 10, 40<= X/R < 120

K = -7.38 x If + 112

Condition 5 5 < If <= 20, 5<= X/R < 40

K = 0.06 x If x (X/R-52.5) + 1.1 x (-X/R+74.9)

Condition 6 10 < If <= 20, 40 <= X/R < 120

K = -0.81 x If + 45

Now If =6.44 and X/R = 30, Hence "Condition 5 is considered", Therefore:

K = 0.06 x x (X/R-52.5) + 1.1 x (-X/R+74.9) 57.13

Vk>= K X (RCT+RI) 328.45V

Vk = 350.00V

Page 13


6

DOC. NO. CU-47000-0202 REV. 01


Eal


Ktd = Ktf = 2 x pi x f x TP x ( 1 - e

(-t'/TP)

)+1

2 x 3.14 x 50 x (0.12) x (1-e(-0.08/0.12)) + 1

Ktd = Ktf = 19.334

Eal


Eal

= 4833.610739

25 x 19.334 x (5+5) x 1

As Equivalent Rated Secondary e.m.f is greater than Knee Point Voltage, CT is capable of supplying Eal to the relay circuit. B.2.10

Results y r a t m i r a P t ) N P d n I e r ( e r t p a u a R C T

) y N S r a I ( d t d n n e o r e c t r a e u R S C


l a t ) r m h o r t h e I ( h S t T n d e r e e r t m u a i R T C

f e ) h o t m l I ( n i t o T a i t t m n r r e a o r r e r u h h u D S T C

c i ) m a n y n d y I ( t D d n e r e r t a u R C


r o l i t t a u c c c a i r r F t i e C t n t m r e r m o r y h u S S C

e m i T t y n r a a t s m n i r o P C


(A) 1600

(A) 1

(Hz) 50

(kA) 40kA

(sec) 1

(kA) 100

(-) TPX

(-) 25

(ms) 120

(-) C-80ms-O

Page 14

e v n i t s e i s d r e u R B

(W) 5W

g n i t i f . m m i . L e . i . u c q e E S

(V) 4834V


DOC. NO. CU-47000-0202 REV. 01

C.1

CT sizing calculation for 400kV Metering Core

C.1.1

Applicable CT and core Numbers: Feeder Detail CT Ratio ICT-1 1600/1 ICT-2 1600/1 ICT-1 1600/1 ICT-2

C.1.2

X/R

C.1.4

C.1.5

This is as per disc ussion had on 12th October 2010, with the view to connect this core for Circuit Breaker Control Switching Scheme

1 50 30

s Hz -


ISN

1

A


RCT

4

W


SN

10

VA

Rated Burden

Instrument Parameter (As per the attached Annexure 1) IM 1 A

o


Sr

0.15

VA

FS

5

-

SM1

1

VA

Rated Burden of Meter -1

SM2

1

VA

Rated Burden of Meter -2

m


Secondary Lead Parameter IL 530

Maximum burden of Bay Control Unit(As per Annexure-I) Instrument Security Factor

6 1 3.746

mm2 W/km

Cross sectional area of leads No of runs of cable connected to CT secondary o AC resistance of 6 Sq.mm Cu, lead at 75 C

1000 765

MVA kV


VS

400

kV

--

14

%

r L

C.1.7

2

Ref. Drawing No. 765/400kV Unnao substation SLD:CU-470000001,Rev.00

CT Parameter (As per Specification ,Vol-III Instrument Transformer 071806-47ES-7230 Rev.0.Cl.2.11.2) IPN 1600 A Rated Primary Current

AL

C.1.6

400-6-CT

Core No. 3 3 2

System Parameter (As per Specification,Vol-II General Technical Requirement 071806-47ES-0200 Rev.0 Cl.6.1) Variable Value Unit Description Vn 400 kV Nominal Voltage Ispec 40 kA Primary Short Circuit Current t f n

C.1.3

1600/1

CT No 400-3-CTT 400-6-CTT 400-3-CT

Transformer P arameter -VP

Secondary Voltage Rating Percentage Impedance(As per Specification,Vol-III 01780647ES-7130 Rev.o Cl.2.8.1,page 3)

Formula and Requirements-Metering

Page 15


1

DOC. NO. CU-47000-0202 REV. 01

Resitive Burden 2

S l e a d

=

(2.IL.RL/1000)*ISN

S T

=

S lead +S r + S M1 + S M2

Two way lead burden in VA ( IL=530 Mtr Longest distance of CT cabling as per Layout) 3.97VA

6.12VA 2

Instrument Secuirty Factor SCT

=

2

RCT *ISN 2

= 5*1 = 4.00VA = FsX(SN+SCT)/(ST+SCT) = 6. 92

FS'

20 X ISN

Rated short time carrying capactiy of Bay Control Unit = = = ISN X FS'

=

1 X 6.92 = 6.92

20*1 20A < 20A

Hence, ISF adopted is <= 5 C.1.8

Results y r a m t i r a P t ) n N P d e I r ( e r t p a u a R C T

) N y r I S a t ( d n d n e r e o t c r a e u R S C

) n f ( y c n e d u e q t a e r R F

l a t ) r m o r h t h e I ( S h t T n d r e e e t r m u a i R T C

f e ) h o t m l I ( n i t o T a n i t t m e a r r r r r o e u h h u D S T C

c i ) m a n y n d y I ( D t n d e r e r t a u R C

n e d r u B d e t a R

r o t c t a n F e y t i m r u r u t s c e n I S

f y o c a s r s u a c l c C a

R

(A) 1600

(A) 1

(Hz) 50

(kA) 40kA

(sec) 1

(kA) 100

(VA) 10

(-) <=5

(-) 0.2

(W) 5

Page 16

T C


DOC. NO. CU-47000-0202 REV. 01

D.1

CT sizing calculation for 400kV Over Current and Earth Fault Protection

D.1.1


D.1.2

D.1.3

D.1.4

D.1.5

Feeder Detail

CT Ratio

CT No

Core

Ref. Drawing No.

ICT-1

1600/1

400-6-CTT

4

ICT-2

1600/2

400-7-CTT

4

765/400kV Unnao substation SLD:CU-470000001,Rev.00


Value

Unit

Vn

420

kV

Nominal Voltage

Description

Ispec

40

kA


t

1

s

f n

50

Hz

X/R

30

-



1600

A


ISN

1

A


RCT

5

W



o


1

A

Sr

0.04

VA

Over Current Protection Relay Burden(Burden & CT Requirement of Micom Relays)

IL

530

m


AL

6

mm2

1

-

3.746

W/ km

Secondary Lead Parameter

r L

Cross sectional area of leads No of runs of cable connected to CT secondary AC resistance of 6 Sq.mm Cu, lead at 75oC

Page 17


D.1.6

D.1.7

DOC. NO. CU-47000-0202 REV. 01

Transformer P arameter --

1000

MVA

VP

765

kV


VS

400

kV


--

14

%

Percentage Impedance(As per Specification,Vol-III 017806-47ES-7130 Rev.o Cl.2.8.1,page 3)


1

Relay Type

2

Rated Current,I R

3

(relay)

: Backup over current Earth fault Protection Micom-P141 : 1A

,t

: 100 X IR for 1s = 100 X 1 A for 1s = 100A

4

Maximum relay Secondary Input Current during through fault, I f :

for 1sec

IPSC/IPN X ISN = 40000/1600 X 1 = 25.00A

D.1.8 1

<100A [Ith(relay)]



2

Through Fault Current on Secondary side of Transformer I PSC(HV):

Fault-MVA/(-/3 XVP) = 7142.86/(1.732*400) = 10.31kA

D.1.9

Formula and Requirements-Backup over current Earth fault Protection The following formulae and requirements are applied

1

Resistive Burden RI = (2.IL.r L /1000)


( IL=530 Mtr Longest distance of CT c abling as per Layout) = (2 X 530 X 3.746 / 1000)

Page 18


DOC. NO. CU-47000-0202 REV. 01

=

2

Rr = Sr/Ir

Relay burden on CT

= 0.04/1^2 =

2

VA Burden and Accuracy class of CT in VA 2

Scal = ISN *(Rl + Rr ) =

Sreq >= Scal

2

SCT = ISN *RCT =

Protection Class of CT Protection Class

5P20

(The 5P20 class CT shall comply within composite error of (+/-) 5% for 20 times the rated CT current flow at rated burden.) Accuracy Limit at Rated Burden, ALFr

= 20

Rated Burden of CT, VAr

= 30.00VA

Actual Buden

= 4.01VA

Accuracy Limit at Rated Burden, ALFr

= ALFr * (VAr + SCT)/(Sreq + SCT) 78

Ohm

Accuracy Limit Current referred to the secondary of the CT for 5P20

= Accuracy Limit at Rated Burden, ALFr * Ir 78A

Page 19

PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT S IZING ITEM CODE 7235-1B/2B

DOC. NO. CU-47000-0202 REV. 01

The CT secondary current during = Ipsc/IP X Is

max system fault condition

= (10.31 X 1000)/1600 X 1 = 6.44A

Since the maximum fault current seen by the CT is less than the Accuracy Limit Current We infer that the composite error will be within the limit. Hence 5P20 class, 30VA CT is adequate. D.1.10

Results y r a m t i r a ) P t N P d n I e ( e r t r p a u a R C T

) N y r S a I ( d t n n d o e e c r t r a e u R S C


l a t ) r m o r h t h e I ( S h t d T n e e r e t r m u a i R T C

f e ) h o t m l I ( n i o T a t n i t t m e r r a r o e r r u h h u D S T C

c i ) m a n y n d y I ( D t d n e e r t r a u R C



R

(A) 1600

(A) 1

(Hz) 50

(kA) 40kA

(sec) 1

(kA) 100

(-) 5P20

(VA) 30

(W) 5

Page 20

T C


DOC. NO. CU-47000-0202 REV. 01

D.2

CT sizing calculation for 400kV LBB, Over current and Earth Fault Protection

D.2.1


D.2.2

D.2.3

D.2.4

Feeder Detail

CT Ratio

CT No

Core

ICT-1

1600/1

400-6-CT

3

ICT-2

1600/2

400-7-CT

3



Value

Unit

Description

Vn

420

kV

Nominal Voltage

Ispec

40

kA


t

1

s

f n

50

Hz

X/R

30

-



1600

A


ISN

1

A


RCT

5

W


o

Relay Parameter (As per the attached Annexure 1) IR Sr

1 0.04

A VA

Rated Input Current of BCU used Over Current Protection Relay Burden(Burden & CT Requirement of Micom Relays)

Page 21


D.2.5


100

m

AL

6

mm2

1

-

3.746

W/ km

--

1000

MVA

VP

765

kV

Primary Voltage Rating

VS

400

kV


--

14

%

Percentage Impedance(As per Specification,Vol-III 017806-47ES-7130 Rev.o Cl.2.8.1,page 3)

r L

D.2.6

D.2.7

DOC. NO. CU-47000-0202 REV. 01



Transformer Parameter Transformer MVA Rating


1

Relay Type

2

Rated Current,I R

3

(relay)

Breaker Failure, Backup Over Current & Earth fault Protection Micom: P821/141 : 1A

,

: 100 X I R for 1s = 100 X 1 A for 1s = 100A

4

Maximum relay input current during through fault, I f

=

for 1sec

IPSC/IPN X ISN = 40000/1600 X 1 = 25.00A

Page 22

<100A [Ith(relay)]


D.2.8 1

DOC. NO. CU-47000-0202 REV. 01



2

Through Fault Current on Seconary side of Transformer If(MV):

Fault MVA/(-/3 XVP) = 7142.86/(1.732*400) =

D.2.9

10.31kA

Formula and Requirements-Backup over current Earth fault Protection The following formulae and requirements are applied

1

Resistive Burden RI = (2.IL.r L /1000)


( IL=530 Mtr Longest distance of CT cabling as per Layout) = (2X350X3.746/1000) =

2

Rr = Sr/Ir

= 0.04/1^2 =

2

VA Burden and Accuracy class of CT in VA

Page 23

Relay burden on CT


DOC. NO. CU-47000-0202 REV. 01 2

Scal = ISN *(Rl + Rr ) =

Sreq >= Scal

2

SCT = ISN *RCT =

Protection Class of CT Protection Class

5P20


=

20

Rated Burden of CT, VAr

=

30.00VA

Actual Buden

=

0.79VA


=

ALFr * (VAr + SCT)/(Sreq + SCT) 174 VA

Accuracy Limit Current referred to the secondary of the CT for 5P20

=

Accuracy Limit at Rated Burden, ALFr * Ir 174A

The CT secondary current during max system fault condition

=

Ipsc/IP X Is

=

(10.31 X 1000)/1600 X 1

Page 24

Based on Through Fault Current at D.2.8-(2)


DOC. NO. CU-47000-0202 REV. 01

=

6.44A

Since the maximum fault current seen by the CT is less than the Accuracy Limit Current We infer that the composite error will be within the limit. Hence 5P20 class, 30VA CT is adequate.

D.2.10

Results

t a t n e r r u C y r a m i r ) P N P d I e ( t p a a R T

y r a d n ) o N c S e I t S ( n d e r e r t a u R C

) n f ( y c n e u q e r F d e t a R

) h t e I ( t m n i T e r r t r u o C h l S a d m e r t e a h R T

e ) m i t T h I t ( r t o n h e r S r f u o C n l o a i t m r a r e u h D T

c i ) m a n y n d y I ( t D n d e r e r t a u R C

C E I r e p s a s s a l C


R

(A)

(A)

(Hz)

(kA)

(sec)

(kA)

(-)

(VA)

(W)

1600

1

50

40kA

1

100

5P20

30

5

Page 25

T C


DOC. NO. CU-47000-0202 REV. 01

E.1

CT sizing calculation for 400kV TEE-Protection

E.1.1


E.1.2

E.1.3

Feeder Detail

CT Ratio

CT No

ICT-1

3000/1

400-6-CTT

ICT-2

3000/1

400-7-CTT

ICT-1

3000/1

400-6-CT

ICT-2

3000/1

400-7-CT

Ref. Drawing No.

5

765/400kV Unnao substation SLD:CU-47000-0001,Rev.00


Value

Unit

Vn

420

kV

Nominal Voltage

Ispec

40

kA


t

1

s

f n

50

Hz

X/R

30

-

Description



E.1.4

Core

3000

A


ISN

1

A


RCT

6.8

W


o


1

A

Sr

0.025

VA

Maximum Protective relay Burden(Burden & CT requirement of Micom relays)

tm

30

ms


IS

0.1

-

tcb

40

ms


Minimum Setting of Relay Circuit Breaker Operating Time

Page 26

PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B E.1.5


530

m

AL

6

mm2

1

-

3.746

W/km

r L

E.1.6

E.1.7

DOC. NO. CU-47000-0202 REV. 01




1000

MVA

VP

765

kV


VS

400

kV


--

14

%

Percentage Impedance(As per Specifi cation,Vol-III 017806-47ES-7130 Rev.o Cl.2.8.1,page 3)


1

Relay Type

: Connection Diffrential, Micom P122

2

Rated Current,I R

: 1A

3

capacity,Ith (relay)

: 100 X I R for 1s = 100 X 1 A for 1s = 100A

4

Maximum reay input current during through fault, I f

for 1sec

IPSC /IPN X ISN = 40000/3000 X 1 = 13.33A

5


<100A [Ith(relay)]

= MVA/(-/3 x V P) = 1000 X 1000/1.732 X 400 = 1443A

E.1.9

Formula and Requirements-Metering The following formulae and requirements are applied

1

Rated Symmetrical Short Circuit Current factor(K sec) KSSC

As per IEC 44-6(Cl.3.15) = IPSC/IPN

Page 27


DOC. NO. CU-47000-0202 REV. 01

= 40000 X 1000/3000 = 13.33


2

= 17.5


Primary Time Constant(T P) For the System Close in Fault

X/R= 30 L/R= 30/(2X3.14X50)

Therefore Primary Time Constant(T P) at system fault

=

0.096sec = 95.54msec

Standard Value of TP

3

= 120



= C-t'-O

where t' = Duration of first current flow t'= tm + tcb = 70ms Selected Duty Cycle

4

(Say 80 ms)

= C-80ms-O

Resistive Burden(External Burden) RI = ( 2.IL.r L /1000)


( IL=530. Mtr Longest distance of CT cabling as per Layout) = (2X530X3.746/1000) =

2

Rr = Sr/Ir

Relay burden on CT

= 0..025/1^2 =

Rb = RI+Rr =

Page 28


DOC. NO. CU-47000-0202 REV. 01


5

=


Stabilising Voltage >= If x (Rl + RCT) x ((0.007 x X/R) + 1.05)

Vs

>= 13.33 X (3.97 + 6.8) X ((0.007 X 30) + 1.05) >= 180.95V

6

Knee Point Voltage

Vk

>= 4 X Vs >= 4 X 151 >= 604

Adopted Vk

7

= 630V

Calculation of stabilizing resistor

Relay setting Voltage

Vs

= 180.95V

Relay setting Current

Is

= 0.1

Relay Burden

Sr

= 0.025

Relay Resistance

Rrelay

= 2.5

Stabilising Resistor

= (Vs/Is) - Rrelay = 1807 ohms

8


Eal Ktd = Ktf =

= Kssc x Ktd x (RCT + Rb) x ISN 2 x pi x f x T P x ( 1 - e

(-t'/TP)

)+1

2 x 3.14 x 50 x (120/1000) x (1-e(-0.08/0.12)) + 1

Page 29


DOC. NO. CU-47000-0202 REV. 01

Ktd = Ktf =

38.632

Eal

= 15 x 38.632 x (6.8 + 5) x 1

Eal

=

7978V

As Equivalent Rated Secondary e.m.f is greater than Knee Point Voltage, CT is capable of supplying Eal to the relay circuit. E.1.10 Results y r a t m i r a ) P t N n P d e I ( e r t r p a u a R C T

(A) 3000

a ( d t n d n e o e t c r r a e u R S C

) n f ( y c n e d u e t q e a r R F

l a t ) r m h o r t I h e ( S h t n d T e e r e t r m u a i R T C

f e ) h o t I m l ( n i t o T a n i t t m e r r a r o e r r u h h u D S T C

c i ) m a n y n d y I ( D t n d e e r t r a u R C


r o l i t t a u c c c a i r i r F t e C t n t m e r r m o r y h u S S C

e m i T t n y r t a a s m n i r o P C

(A) 1

(Hz) 50

(kA) 40kA

(sec) 1

(kA) 100

(-) TPX

(-) 17.5

(ms) 120

)

N y r I S

Page 30


(-) C-80ms-O

e v i t n s e i s d r e u R B

(W) 5W

. c e S g n f i . t i . i u m m q i . E L e (V) 7978V


DOC. NO. CU-47000-0202 REV. 01

400KV CT PARAMETERS FOR 765KV UNNAO SUBSTATION DESCRIPTION 7235-1B-400kV Bus Protection Type Relay Type Ratio Accuracy class Burden(ohm for TPX & VA for 5P20, Metering) Primary Time Constant (ms) Kssc Duty Cycle RCT (ohm) Equivalent Limiting Scondary e.m.f (V) Ie (mA) at above Voltage offered

CORE 1

CORE 2

Bus-Bar Protection

Metering*

ABB-RADSS 2000:1 TPX

BCU 1600:1 0.2

CORE 3

CORE 4

LBB, O/C and E/F Protection Micom-P141/821 1600:1 5P20

Transformer Diffrential Protection Micom-P643 1600:1 TPX

CORE 5 TEE Protection Micom-P122 3000:1 TPX

15

10

30

5

5

120 20 C - 0.08sec - O 5.5 5142 <=30

NA NA NA 5 NA NA

NA NA NA 5 NA NA

120 25 C - 0.08sec - O 5 3089 <=30

120 17.5 C - 0.08sec - O 6.8 3645 <=20

NOTE * : This is as per discussion had on 12th October 2010, with the view to connect this core for Circuit Breaker Control Switching Scheme 7235-2B-400kV ICT Protection Type

Spare

Relay Type Ratio Accuracy class Burden(ohm for TPX & VA for 5P20, Metering) Primary Time Constant (ms) Kssc Duty Cycle RCT (ohm)

2000:1 5P20

Equivalent Limiting Scondary e.m.f (V) Ie (mA) at above Voltage offered

Transformer Diffrential Protection Micom-P633 1600:1 TPX

Metering

O/C and E/F Protection

TEE Protection

BCU+Energy Meter 1600:1 0.2

Micom-P141 1600:1 5P20

Micom-P122 3000:1 TPX

30

5

10

30

5

NA NA NA 5 NA NA

120 25 C - 0.08sec - O 5 3089 <=30

NA NA NA 5 NA NA

NA NA NA 5 NA NA

120 17.5 C - 0.08sec - O 6.8 3645 <=20


DOC. NO. CU-47000-0202 REV. 01 CROMPTON GREAVES LTD ENGINEERING PROJECT DIVISION-GURGAON

Project Client Consultant Title Sl. No C1. 1

2

3 4 5 6 7 8

C2.

765KV Substation at UNNAO Uttar Pradesh Power Transmission Corporation Limited SNC-Lavalin Compliance Statement for 400kV CT-Sizing w ith reference to SNC mail dated 5/10/2010 & Conference call on 6/10/2010. Description Subject: General The pages of the document are not numbered hence it is not possible to c omment with page reference.The same may be numbered. CT Sizing calculation format of 765kv CTs for Unnao s/s may be follozed to maintain similarly of the CTs sizing document.For calculation refer to 765kv CT calculation refer to 765kv CT CALCULATION AND FOLLOW iec 44-6 recommendation for calculation of Eal.Please indicate le (Ma) at this voltage. For LBB protection 40kA must be considered (It must cover bushing faults too).Calculation may be revised accordingly Please confirm that existing BB Protection CTs have 2000/1 CTR. To cover Bushing faults,design CT based on 40k A,KSSC=40kA/1600=25 Recalculate duty cycle with relay operating time of 80ms and CB operating time of 40ms .The duty cycle will be C-80 O. For over current protection 40kA must be considered and recalculate accordingly. A copy of page regarding 765kV CT summary of Unnao s/s is attached.For 400kV CT similar summary sheet may be prepared after arriving at the final parameter by doing calculations following the 765kV CT calculation format.

CGL Reply Noted & Complied

Noted & Complied

Noted & Complied Noted & Complied Noted & Complied Noted & Complied Noted & Complied Noted & Complied

Subject: 400kV ICT CT, 7235-2B, 400-6-CTT & 400-7-CTT Core1: Modify core no1(spare core) to 5P20 with 40VA power-5P Class,30VA,ALF=20 Noted & Complied Core2: The different parameters shall be as follows .Symmetrical SC current factor should be taken 25 instead of 7.5 .Primary time constant-120ms instead of 100ms. .Specified duty cycle-C-80-O instead of 100ms

Noted & Complied


DOC. NO. CU-47000-0202 REV. 01 CROMPTON GREAVES LTD ENGINEERING PROJECT DIVISION-GURGAON

Project Client Consultant Title Sl. No

C3.

765KV Substation at UNNAO Uttar Pradesh Power Transmission Corporation Limited SNC-Lavalin Compliance Statement for 400kV CT-Sizing w ith reference to SNC mail dated 5/10/2010 & Conference call on 6/10/2010. Description Core3: Meeting core should be of 1600/1 CTR .The rated burden should be 10 instead of 30. .Separate column to be added for Rct

CGL Reply Noted & Complied

Core4: Separate column to be added forRct

Noted & Complied

Core5: CTR not mentioned , it should be 3000/1 .Rated secondary current written as 420A should be corrected as 1Amp. .Symmetrical S.C current factor should be 17.5 instead of 15 .Primary time constant should 120ms instead of 100ms .Specified duty cycle-C-80-O SHOULD BE T ACKEN.

Noted & Complied

Subject: 400kV Bus CT, 7235-1B, 400-6-CT & 400-7-CT Core1: should be used for TEE protection

As per PSLD-CU-47000-0058, Core 1 is used for B/B Protection Core 5 is used for TEE-Protection

.CTR not mentioned should be 3000/1 and secondary ampere should be 1Amp instead of 420Amp .Symmetrical S.C current factor should be 17.5 instead of 15 Noted and Complied for Core 5 .Primary time constant should 120ms instead of 100ms .Specified duty cycle-C-80-O instead of C-100-O. .Break operating time tcb should be taken on 40ms in place of 45ms.

CT-Sizing

Recommend Documents