1X660MW BHUSAWAL PROJECT
STABILITY TEST OF STATION TRANSFORMER #6B DATE: / /
Time:
3-phase 415VAC supply is applied at switchyard before CT.
1. DIFFERENTIAL PROTECTION STABILITY CHECK:
The stability of Differential & REF protection checked by three phase shorting at 11KV
Switchgear after CT. With this arrangement all the differential, REF and protection CT’s are
carrying the current.
Primary voltage at switchyard: -R-Y - V, Y-B - V, B-Y - V,
Primary current at switchyard: - R-ph - A, Y-ph - A, B-ph - A,
Primary Current at 11KV Switchgear: - A
LV1 (R-Y-B) & LV2 (R-Y-B) SHORTED after CT at Line PT (OBC & OBD CT’S ARE IN
SERVICE).
CURRENT MEASUREMENT AT STRP PANEL:-
(All Current values in mA)
Phase 400KV side CT
CT-B, Core1, 500/1A, Differential CT-B, Core2, 500/1A, O/C
TB No. Current Current in TB No. Current Current in
(mA) Relay P643 (mA) Relay P643
R-ph TB1-20 IA-a TB1-41
Y-ph TB1-21 IA-b TB1-42
B-ph TB1-22 IA-c TB1-43
N TB1-23 TB1-45
Phase 400KV side CT 11KV Switchgear Side CT- 11KV Switchgear Side
1A,Core-1 CT-1B,Core-1
CT-B, Core3, 500/1A, CTR-3500/1A CTR-3500/1A
Measurement ECP Differential Differential
TB No. Curr Readin TB Current Current TB Curren Current
ent g on No. (mA) in No. t in
(mA) Energy Relay (mA) Relay
Meter P643 P643
R-ph 2TBR- TB1- IB-a TB1- IC-a
15 4 12
Y-ph 2TBR- TB1- IB-b TB1- IC-b
16 5 13
B-ph 2TBR- TB1- IB-c TB1- IC-c
17 6 14
N TB1- TB1-
7 15
CURRENT RECORDED AT DIFFERENTIAL RELAY P643:-
Phase HV side 11KV OBC 11 KV OBD Differential Bias
Switchyard CT Switchgear Switchgear Current (Id) Current
Current Side CT Side CT (Ir)
Current Current
R-ph TB1-20 TB1-4 TB1-12
Y-ph TB1-21 TB1-5 TB1-13
B-ph TB1-22 TB1-6 TB1-14
N TB1-23 TB1-7 TB1-15
REMARKS:-
NEUTRAL SIDE AND REF CT CURRENTS AT STRP:-
Stand by E/F Prot REF Protection
Line Side Neutral Side Differen Current
TB Curr Current in TB Curre TB No. Curre tial in Relay
No. ent Relay No. nt nt Current
P643/P14
1
HV TB1- IY-a HV STRP TB
(P643) 27/28 (P643) TB1-
250/1, 1/2
CT-3,Core- 250/1,
1 CT- Ph
3,Core-2 TB-
(N) & CT-
4,Core-1
(Ph)
LV1 TB1- LV1 STRP IY-b TB
(P141) 9/11 (P141) TB1-
300/1, 3500/1A 30/31
CT- ,CT-2A
2A,Core-1 ,Core-2 Ph
(N) & CT- TB-
1A,Core-2
(Ph)
LV2 TB1- LV2 STRP IY-c TB
(P141) 17/18 (P141) TB1-
300/1, 3500/1A 33/34
CT- ,CT-2B
2B,Core-1 ,Core-2
(N) & CT- Ph
1B,Core-2 TB-
(Ph)
REMARKS:-
CURRENTS AT TRANSFORMER MB:-
Purpose CT Ratio TB No. Current in mA
HV WTI CT-1 159/3.0 -2.7-2.4A X9-1/2
11KV LV1 side WTI 2762/3.5-3.2-2.7A X9-5/6
CT (CT-2)
11KV LV2 side WTI 2762/3.5-3.2-2.7A X9-9/10
CT (CT3)
HV Turret CT (HV CT-4,5,6, 250/1 A (PHASE R ph-X9-25/26
REF) SIDE) Y ph-X9-27/28
B ph-X9-29/30
HV Neutral CT CT-7, CORE1, S E/F CT- X9-31/32
250/1A
CT-3, CORE2, REF CT- X9-33/34
250/1A
LV1 Neutral CT CT-8, CORE1, S E/F CT- X9-35/36
300/1A
CT-8, CORE2, REF CT- X9-37/38
3500/1A
LV2 Neutral CT CT-9, CORE1, S E/F CT- X9-39/40
300/1A
CT-9, CORE2, REF CT- X9-41/42
3500/1A
CURRENTS AT SWITCHGEAR:-
CT Phase 11 KV switchgear Side CT-1 11 KV switchgear Side CT-2
purpose Protection CTR- 3500/1A Core-1, Protection CTR- 3500/1A Core-1,
Metering CTR- 3500/5A Core-2 Metering CTR- 3500/5A Core-2
TB No. Current Current in TB No. Current Current in relay
relay
O/C R TB3-1 TB3-1
Protection Y TB3-3 TB3-3
CT B TB3-5 TB3-5
N TB3-11 TB3-11
REF CT R TB3-19 TB3-19
Y TB3-20 TB3-20
B TB3-21 TB3-21
N TB3-24 TB3-24
Metering R TB3-12 TB3-12
CT Y TB3-13 TB3-13
B TB3-14 TB3-14
N TB3-15 TB3-15
Differential R TB3-26 TB3-26
Protection Y TB3-27 TB3-27
CT B TB3-28 TB3-28
N TB3-31 TB3-31
Remarks:-
During Station Transformer Stability Test, Current in all CT’s related to Station Transformer are
measured & recorded as above to ensure the healthiness of all CT’s.
DIFFERENTIAL PROTECTION STABILITY CHECK:-
LV1 (R-Y-B) & LV2 (R-Y-B) SHORTED after CT at Line PT (OBC & OBD CT’S ARE IN
SERVICE).
CURRENT RECORDED AT DIFFERENTIAL RELAY P643:-
Phase HV side 11KV 11KV Switchgear Differential Bias Current
Switchyard CT Switchgear Side CT Current Current
current Side CT
Current
R-ph TB1-20 TB1-4 TB1-12
Y-ph TB1-21 TB1-5 TB1-13
B-ph TB1-22 TB1-6 TB1-14
N TB1-23 TB1-7 TB1-15
HV S/Y CT R PHASE: SHORTED WITH NEUTRAL.
Phase HV side 11KV 11KV Switchgear Differential Bias Current
Switchyard CT Switchgear Side CT Current Current
current Side CT
Current
R-ph TB1-20 TB1-4 TB1-12
Y-ph TB1-21 TB1-5 TB1-13
B-ph TB1-22 TB1-6 TB1-14
N TB1-23 TB1-7 TB1-15
LV1 11KV CT Y PHASE SHORTED WITH NEUTRAL
Phase HV side 11KV 11KV Switchgear Differential Bias Current
Switchyard CT Switchgear Side CT Current Current
current Side CT
Current
R-ph TB1-20 TB1-4 TB1-12
Y-ph TB1-21 TB1-5 TB1-13
B-ph TB1-22 TB1-6 TB1-14
N TB1-23 TB1-7 TB1-15
LV2 11KV CT B PHASE SHORTED WITH NEUTRAL
Phase HV side 11KV 11KV Switchgear Differential Bias Current
Switchyard CT Switchgear Side CT Current Current
current Side CT
Current
R-ph TB1-20 TB1-4 TB1-12
Y-ph TB1-21 TB1-5 TB1-13
B-ph TB1-22 TB1-6 TB1-14
N TB1-23 TB1-7 TB1-15
Remarks: -Transformer Differential Protection Sensitivity Proved.
1. HV REF STABILITY:-
LV-1 and LV-2 all three phase shorted and HV neutral open.415V applied between
Phase and Neutral of HV side one by one for all three phases.
Voltage applied: - R-N= V, B-N= V, Y-N= V
Primary Current Measured: - R phase= Amp. Y phase= Amp.
B phase= Amp.
Phase Primary Current in MB Current in STRP
Current TB No. Current TB No. Current
R-ph REF Phase-X9 -
25/26
REF Neutral-X9 –
33/34
REF Differential TB1- 1-2
S/by E/F-X9 -31/32 TB1- 27-28
Y-ph REF Phase-X9-
27/28
REF Neutral-X9 –
33/34
REF Differential TB1- 1-2
S/by E/F-X9 -31/32 TB1- 27-28
B-ph REF Phase-X9-
29/30
REF Neutral-X9 –
33/34
REF Differential TB1- 1-2
S/by E/F-X9 -31/32 TB1- 27-28
Remark: - Since differential Current of HV REF CT’s is almost Zero, HV REF Protection Stability
is proved.
2. HV REF SENSITIVITY:-
LV-1 and LV-2 all three phase shorted and HV neutral open. 415V applied between B-
Phase and Neutral of HV side. B-phase HV Turret CT Polarity reversed at Station
Transformer MB.
Phase Primary Current in MB Current in STRP
Current TB No. Current TB No. Current
B-ph REF Phase-X9-
29/30
A REF Neutral-X9 –
33/34
Differential TB1- 1-2 mA
S/by E/F-X9 -31/32 TB1- 27-28 mA
Remark: - Since differential Current of HV REF CT’s is additive, HV REF Protection Sensitivity is
proved.
B-phase HV Turret CT Polarity reversed at Station Transformer MB.
For confirmation of normalization of B-phase HV Turret CT polarity following test carried
out.
Phase Primary Current in MB Current in STRP
Current TB No. Current TB No. CurrentmA
B-ph REF Phase-X9-29/30
REF Neutral-X9 –
A 33/34
Differential TB1- 1-2
S/by E/F-X9 -31/32 TB1- 27-28
Remark: -B-phase HV Turret CT polarity normalization at Station Transformer MB confirmed.
3. LV1 REF STABILITY: - Switching OFF one phase and Switching ON for remaining 2
phases
TB DETAILS Healthy R Phase OFF & Y, Y Phase OFF & R, B Phase OFF & R,
condition B ON B ON Y ON
Phase
OBC I/C -TB3-
19,20,21
REF Neutral
STMB X9-37/38
REF Differential
STRP TB1-30,31
S/by E/F
STRP TB1-9/11
Switching ON one phase and Switching OFF for remaining 2 phases
TB DETAILS Healthy R Phase ON& Y, Y Phase ON& R, B Phase ON& R,Y
condition B OFF B OFF OFF
Phase
OBC I/C -TB3-
19,20,21
REF Neutral
STMB X9-37/38
REF Differential
STRP TB1-30,31
S/by E/F
STRP TB1-9/11
1. LV2 REF STABILITY: - Switching OFF one phase and Switching ON for remaining 2
phases
TB DETAILS Healthy R Phase OFF & Y, Y Phase OFF & R, B Phase OFF & R,
condition B ON B ON Y ON
Phase
OBD I/C -TB3-
19,20,21
REF Neutral
STMB X9-42/43
REF Differential
STRP TB1-33/34
S/by E/F
STRP TB1-17/18
Switching ON one phase and Switching OFF for remaining 2 phases
TB DETAILS Healthy R Phase ON& Y, Y Phase ON& R, B Phase ON& R,Y
condition B OFF B OFF OFF
Phase
OBD I/C -TB3-
19,20,21
REF Neutral
STMB X9-42/43
REF Differential
STRP TB1-33/34
S/by E/F
STRP TB1-17/18
LV1 REF PROTECTION STABILITY & SENSITIVITY: -
415V, 3-ph Voltage applied to HV S/Y side and each phase is shorted to earth one by one at
11KV Switchgear end after CT. Currents are measured at STRP to prove the stability of LV REF
protection.
LV1 REF Protection Stability- 11KV:-
REF CTR: 3500/1A Standby E/F CT: 300/1A
Phase Primary Current in MB Current in STRP
Current TB No. Current TB No. Current
R-ph REF Phase-TB3 -19
REF Neutral-X9-37/38
REF Differential (In Zone) TB1- 30/31
REF Differential (Out of Zone)
S/by E/F-X9 -35/36 TB1- 9/11
Y-ph REF Phase-TB3 -20
REF Neutral-X9-37/38
REF Differential (In Zone) TB1- 30/31
REF Differential (Out of Zone)
S/by E/F-X9 -35/36 TB1- 9/11
B-ph REF Phase-TB3 -21
REF Neutral-X9-37/38
REF Differential (In Zone) TB1- 30/31
REF Differential (Out of Zone)
S/by E/F-X9 -35/36 TB1- 9/11
Remark: - Since differential current is zero in out of zone, LV-1 REF Protection Stability is
proved & Since differential current is equal to neutral current, LV-1 REF Protection Sensitivity is
proved.
LV2 REF PROTECTION STABILITY & SENSITIVITY: -
415V, 3-ph Voltage applied to HV S/Y side and each phase is shorted to earth one by one at
11KV Switchgear end after CT. Currents are measured at STRP to prove the stability of LV REF
protection.
LV2 REF Protection Stability- 11KV:-
REF CTR: 3500/1A Standby E/F CT: 300/1A
Phase Primary Current in MB Current in STRP
Current TB No. Current TB No. Current
R-ph REF Phase-TB3 -19
REF Neutral-X9-42/43
REF Differential (In Zone) TB1- 33/34
REF Differential (Out of Zone)
S/by E/F-X9 -39/40 TB1- 17/18
Y-ph REF Phase-TB3 -20
REF Neutral-X9-42/43
REF Differential (In Zone) TB1- 33/34
REF Differential (Out of Zone)
S/by E/F-X9 -39/40 TB1- 17/18
B-ph REF Phase-TB3 -21
REF Neutral-X9-42/43
REF Differential (In Zone) TB1- 33/34
REF Differential (Out of Zone)
S/by E/F-X9 -39/40 TB1- 17/18
Remark: - Since differential current is zero in out of zone, LV-2 REF Protection Stability is
proved & Since differential current is equal to neutral current, LV-2 REF Protection Sensitivity is
proved.
BHEL MSPGCL(Project) MSPGCL(TESTING) MSETCL(TESTING)
