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
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 TITLE: 400kV CT SIZING ITEM CODE 7235
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
As per IEC 44-6(Cl.4.3)
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235
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
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
Description
Ispec
40
kA
Primary Short Circuit Current
t
1
s
f n
50
Hz
X/R
30
-
Maximum duration of short circuit current System supply Frequency X/R ratio of system
CT Parameter (As per Specification ,Vol-III Instrument Transformer 071806-47ES-7230 Rev.0.Cl.2.11.2) IPN
1600
A
Rated Primary Current
ISN
1
A
Rated Secondary Current
RCT
5
W
CT Resistance at 75 C
Rated Input Current of Relay used
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
Minimum Setting of Relay
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)
As per IEC 44-6(Cl.3.15)
KSSC
= Ispec/IPN = 40 X 1000/1600 = 25.00
Standard Value of KSSC
2
= 25
As per IEC 44-6(Cl.4.1)
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 T P
3
= 120
As per IEC 44-6(Cl.4.3)
Duty Cycle(C-O) Single Energisation
= 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)
Two way lead resistance
( 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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01 Rb = RI+Rr = 2.722W
Standard Value of Rb
5
= 5.00W
Knee Point Voltage
Condition 1
Vk>= K X (RCT+RI)
Applicable If x (X/R)
Condition 2
As per IEC 44-6(Cl.4.5)
<= 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
Rated Equivalent Rated Secondary e.m.f
Eal
= Kssc x Ktd x (RCT + Rb) x ISN
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01 Ktd = Ktf = 19.33
Eal
= Kssc X Ktd X (Rct + Rb) X Isn
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01
B.2
CT sizing calculation for 400kV Transformer Differential Protection(87TB)-Low Impedace Protection
B.2.1
Applicable CT and core Numbers:
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
Ref. Drawing No. 765/400kV Unnao substation SLD:CU-47000-0001,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
Description
Ispec
40
kA
Primary Short Circuit Current
t
1
s
f n
50
Hz
X/R
30
-
Maximum duration of short circuit current System supply Frequency X/R ratio of system
CT Parameter (As per Specification ,Vol-III Instrument Transformer 071806-47ES-7230 Rev.0.Cl.2.11.2) IPN
1600
A
Rated Primary Current
ISN
1
A
Rated Secondary Current
RCT
5
W
CT Resistance at 75 C
Rated Input Current of BCU used
o
Relay Parameter (As per the attached Annexure 1) IR
1
A
Sr
0.2
VA
Maximum Protective relay Burden(Burden & CT r equirement of Micom relays)
tm
30
ms
Transformer Differential Relay Operating time(As per Annexure-I)
IS
0.02
-
Minimum Setting of Relay
tCB
40
ms
Minimum Setting of Relay
IL
100
m
Single way length of leads
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
AC resistance of 6 Sq.mm Cu, lead at 75 C
Page 10
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
B.2.6
B.2.7
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/Specificati on,Vol-III 017806-47ES-7130 Rev.o Cl.2.8.1,page 3 & GTP)
Details of Relay Proposed
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
Full load Current,I L
<100A [Ith(relay)]
= MVA/(-/3 x V P) = 1000 X 1000/1.732 X 400 = 1443A
B.2.8 1
Through Fault Current Through Fault MVA of Transformer
: MVA Rating/% Impedance = 1000 X 100/14 = 7142.86MVA
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
B.2.9
DOC. NO. CU-47000-0202 REV. 01
Formula and Requirements-Metering
The following formulae and requirements are applied 1
As per IEC 44-6(Cl.3.15)
Rated Symmetrical Short Circuit Current factor(K sec)
KSSC
= Ispec/IPN = 40 X 1000/1600 = 25.00
Standard Value of KSSC
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
Standard Value of T P
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
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) = (2X100X3.746/1000) =
2
Rr = Sr/Ir
Relay burden on CT
= 0.2/1^2 =
Page 12
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01
Rb = RI+Rr = 0.949W
Standard Value of Rb
5
=
Knee Point Voltage
As per IEC 44-6(Cl.4.5)
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
6
DOC. NO. CU-47000-0202 REV. 01
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
= 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
) 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 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 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) 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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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 -
Maximum duration of short circuit current System supply Frequency X/R ratio of system
ISN
1
A
Rated Secondary Current
RCT
4
W
CT Resistance at 75 C
SN
10
VA
Rated Burden
Instrument Parameter (As per the attached Annexure 1) IM 1 A
o
Rated Input Current of BCU used
Sr
0.15
VA
FS
5
-
SM1
1
VA
Rated Burden of Meter -1
SM2
1
VA
Rated Burden of Meter -2
m
Single way length of leads
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
Transformer MVA Rating Primary Voltage Rating
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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
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PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01
D.1
CT sizing calculation for 400kV Over Current and Earth Fault Protection
D.1.1
Applicable CT and core Numbers:
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
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
Description
Ispec
40
kA
Primary Short Circuit Current
t
1
s
f n
50
Hz
X/R
30
-
Maximum duration of short circuit current System supply Frequency X/R ratio of system
CT Parameter (As per Specification ,Vol-III Instrument Transformer 071806-47ES-7230 Rev.0.Cl.2.11.2) IPN
1600
A
Rated Primary Current
ISN
1
A
Rated Secondary Current
RCT
5
W
CT Resistance at 75 C
Rated Input Current of Relay used
o
Relay Parameter (As per the attached Annexure 1) IR
1
A
Sr
0.04
VA
Over Current Protection Relay Burden(Burden & CT Requirement of Micom Relays)
IL
530
m
Single way length of leads
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
D.1.6
D.1.7
DOC. NO. CU-47000-0202 REV. 01
Transformer P arameter --
1000
MVA
VP
765
kV
Transformer MVA Rating Primary Voltage Rating
VS
400
kV
Secondary Voltage Rating
--
14
%
Percentage Impedance(As per Specification,Vol-III 017806-47ES-7130 Rev.o Cl.2.8.1,page 3)
Details of Relay Proposed
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)]
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(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)
Two way lead resistance
( IL=530 Mtr Longest distance of CT c abling as per Layout) = (2 X 530 X 3.746 / 1000)
Page 18
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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
) n f ( y c n e d u e q t e a r R F
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 e p s a s s a C l E C I
n e d r u B d e t a R
R
(A) 1600
(A) 1
(Hz) 50
(kA) 40kA
(sec) 1
(kA) 100
(-) 5P20
(VA) 30
(W) 5
Page 20
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PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01
D.2
CT sizing calculation for 400kV LBB, Over current and Earth Fault Protection
D.2.1
Applicable CT and core Numbers:
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
Ref. Drawing No. 765/400kV Unnao substation SLD:CU-47000-0001,Rev.00
System Parameter (As per Specification,Vol-II General Technical Requirement 071806-47ES-0200 Rev.0 Cl.6.1) Variable
Value
Unit
Description
Vn
420
kV
Nominal Voltage
Ispec
40
kA
Primary Short Circuit Current
t
1
s
f n
50
Hz
X/R
30
-
Maximum duration of short circuit current System supply Frequency X/R ratio of system
CT Parameter (As per Specification ,Vol-III Instrument Transformer 071806-47ES-7230 Rev.0.Cl.2.11.2) IPN
1600
A
Rated Primary Current
ISN
1
A
Rated Secondary Current
RCT
5
W
CT Resistance at 75 C
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
D.2.5
Secondary Lead Parameter IL
100
m
AL
6
mm2
1
-
3.746
W/ km
--
1000
MVA
VP
765
kV
Primary Voltage Rating
VS
400
kV
Secondary Voltage Rating
--
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
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 at 75 C
Transformer Parameter Transformer MVA Rating
Details of Relay Proposed
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)]
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
D.2.8 1
DOC. NO. CU-47000-0202 REV. 01
Through Fault Current Through Fault MVA of Transformer
: MVA Rating/% Impedance = 1000 X 100/14 = 7142.86MVA
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)
Two way lead resistance
( 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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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
Accuracy Limit at Rated Burden, ALFr
=
20
Rated Burden of CT, VAr
=
30.00VA
Actual Buden
=
0.79VA
Accuracy Limit at Rated Burden, ALFr
=
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)
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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
n e d r u B d e t a R
R
(A)
(A)
(Hz)
(kA)
(sec)
(kA)
(-)
(VA)
(W)
1600
1
50
40kA
1
100
5P20
30
5
Page 25
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PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01
E.1
CT sizing calculation for 400kV TEE-Protection
E.1.1
Applicable CT and core Numbers:
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
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 per Specification ,Vol-III Instrument Transformer 071806-47ES-7230 Rev.0.Cl.2.11.2) IPN
E.1.4
Core
3000
A
Rated Primary Current
ISN
1
A
Rated Secondary Current
RCT
6.8
W
CT Resistance at 75 C
o
Relay Parameter (As per the attached Annexure 1) IR
1
A
Sr
0.025
VA
Maximum Protective relay Burden(Burden & CT requirement of Micom relays)
tm
30
ms
Transformer Differential Relay Operating time(As per Annexure-I)
IS
0.1
-
tcb
40
ms
Rated Input Current of BCU used
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
Secondary Lead Parameter IL
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
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 at 75 C
Transformer Parameter --
1000
MVA
VP
765
kV
Transformer MVA Rating Primary Voltage Rating
VS
400
kV
Secondary Voltage Rating
--
14
%
Percentage Impedance(As per Specifi cation,Vol-III 017806-47ES-7130 Rev.o Cl.2.8.1,page 3)
Details of Relay Proposed
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
Full load Current,I L
<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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01
= 40000 X 1000/3000 = 13.33
Standard Value of KSSC
2
= 17.5
As per IEC 44-6(Cl.4.1)
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
As per IEC 44-6(Cl.4.3)
Duty Cycle(C-O) Single Energisation
= 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)
Two way lead resistance
( 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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
DOC. NO. CU-47000-0202 REV. 01
Standard Value of Rb
5
=
As per IEC 44-6(Cl.4.5)
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
Rated Equivalent Rated Secondary e.m.f
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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 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 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
y t u d d e i f i e c l e c p y S C
(-) 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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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
PROJECT: 765kV UNNAO SUBSTATION TITLE: 400kV CT SIZING ITEM CODE 7235-1B/2B
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.