GENERATOR TRANSFORMER TESTING REPORT
LOCATION
GT2
TRANSFORMER DETAILS:
TRANSFORMER SR NO
6004725
CAPACITY
MAKE
VOLTAGE RATIO
VECTOR GROUP
TOTAL TAP
250 MVA
BHEL
15.75/400KV
YNd11
13
1. MAGNETISING CURRENT TEST:
Date: 19/08/2023
INSTRUMENT USED
INSTRUMENT SR NO
multimeter
220451349
Clamp meter
1002002220
APPLIED VOLTAGE(V)
OTI (°C)
TAP POSITION
36
7
MAGNETISING CURRENT(mA)
VR-N
242.4
IR
1.88
VY-N
242.3
IY
1.44
VB-N
242.5
IB
1.89
Points to be remember:
 Apply Single phase AC supply to HV winding and LV winding kept open.
 Compare the value with pre-commissioning values. Any abnormal increase of the order of 50 times
indicates there is a fault inside.
2. CORE BALANCE TEST
Date:19/08/2023
INSTRUMENT USED
INSTRUMENT SR NO
OTI (°C)
WTI (°C)
Multimeter
220451349
36
34
VOLTAGE APPLIED(V)
VOLTAGE MEASURED(V)
R-N
242.4
Y-N
220.7
B-N
23.10
Y-N
242.3
R-N
146.5
B-N
97.7
B-N
242.5
R-N
25.19
Y-N
217.6
Points to be remember:

When extreme phase is excited centre phase shall be 50 to 95% of applied voltage.

When centre phase is excited extreme phase voltage shall be 30 to 75% of the applied
voltage.

Sum of measured induced two phases should equal to the voltage applied.
GENERATOR TRANSFORMER TESTING REPORT
LOCATION
GT2
3. TRANSFORMER TURNS RATIO:
INSTRUMENT USED
ATRT 03 B, Vanguard
Date: 19/08/2023
INSTRUMENT SR NO
LKN 14130
TAP POSITION
OTI (°C)
36
WTI (°C)
34
WINDING COMBINATION
R-N/r-b
Y-N/y-r
B-N/b-y
1
16.170
16.160
16.180
2
15.986
15.975
15.995
3
15.797
15.788
15.807
4
15.605
15.603
15.615
5
15.403
15.399
15.413
6
15.216
15.212
15.230
7
15.011
15.007
15.021
8
14.832
14.820
14.841
9
14.644
14.632
14.654
10
14.456
14.446
14.463
11
14.249
14.245
14.258
12
14.064
14.056
14.077
13
13.863
13.854
13.875
Service tap -07
15.019
15.010
15.026
Points to remember:
 Compare the trend of turns ratio with reference to pre-commissioning values
 The maximum allowable variation of turn’s ratio is ±0.5%.
5. TAN DELTA: file name -2023GT2
DATE- 16/08/2023
INSTRUMENT USED
INSTRUMENT SR NO
Doble M4100
050001343
OTI (°C)
WTI (°C)
36
34
TAN DELTA OF WINDING: File name-GT#2
2KV
TEST MODE
10KV
CAPACITANCE(pf)
28073.00
GAR-R(CH)
TAN DELTA(%)
0.524
CAPACITANCE(pf)
28066.15
TAN DELTA(%)
0.513
GND-RB(CH+CL)
0.518
56630.00
0.528
56590.00
UST-R(CHL)
0.521
28513.35
0.528
28518.70
GAR-R(CL)
0.507
64600.00
0.532
64570.00
GND-RB(CL+CLH)
0.509
93150.00
0.529
93340.00
UST-R(CLH)
0.517
28515.00
0.523
28531.35
GENERATOR TRANSFORMER TESTING REPORT
LOCATION
GT2
TAN DELTA OF BUSHING:
2KV
TEST MODE
10KV
TAN DELTA (%)
CAPACITANCE(pF)
TAN DELTA (%)
CAPACITANCE(pF)
UST-R(R-ph)
0.304
431.38
0.309
431.34
UST-R(Y-ph)
0.329
436.63
0.335
436.55
UST-R(B-ph)
0.277
428.40
0.277
427.74
Points to be remember:
 Allowable limit for tan delta =0.7%, Capacitance =110% of the commissioning value.
 Ensure bushings are clean and free from dust.
 Tan delta test point of bushing should be properly earthed after testing.
6. IR VALUE OF WINDING:
INSTRUMENT USED
Date:08.09.2023
INSTRUMENT SR NO
OTI (°C)
WTI (°C)
2210068279
32
32
Rishab
INSULATION RESISTANCE
WINDING
COMBINATION
TEST VOLTAGE
15SEC
60SEC
600 SEC
HV-E
5KV
239
277
555
LV-E
5KV
204
322
639
HV-LV
5KV
231
377
847
Points to be remember:
 Calculate PI =IR at 10min/IR at 1min, Absorption factor (k) = IR at 60sec / IR at 15sec.
 Recommended PI values are PI < 1.0 –Dangerous, PI between 1.0-1.1 is poor, PI between 1.252.0 is satisfactorily, PI >2 is good.
 Ensure bushings are clean and free from dust.
GENERATOR TRANSFORMER TESTING REPORT
LOCATION
GT2
7. WINDING RESISTANCE OF HV WINDING:
INSTRUMENT USED
Date: 06.09.2023
INSTRUMENT SR NO
OTI (°C)
2307-02U481
32
TRM25,Scope T&M Pvt. Ltd.
WINDING RESISTANCE ( mΩ )
TAP POSITION
WTI (°C)
32
TEST CURRENT
R-N
Y-N
B-N
10A
1
932
934
934
10A
2
924
924
925
10 A
3
920
920.1
919
10 A
4
907.1
910
910
10 A
5
901
903
903
10 A
6
892
894
894
10A
7
884
884
885
10A
8
891
894
894
10A
9
901
903
903
10 A
10
910
909
910
10 A
11
920
921
921
10 A
12
926.0
926
926
10 A
13
933
934
934
10A
885
884
884
10A
SERVICE TAP-07
8.WINDING RESISTANCE OF LV WINDING:
DATE 08.09.2023
INSTRUMENT USED
INSTRUMENT SR NO
OTI (°C)
WTI (°C)
TRM25,Scope T&M Pvt. Ltd.
2307-02.U481
32
32



WINDING
r-y
y-b
b-r
WINDING RESISTANCE
1652µΩ
1652µΩ
1653µΩ
TEST CURRENT(A)
25
25
25
Points to be remember:
Trend in variation shall be same. Deviation in absolute values to be within ±5%.
This test shall be the last on winding to avoid possibility of erroneous test results during
subsequent tests because of core saturation.
GENERATOR TRANSFORMER TESTING REPORT
LOCATION
GT2
9. IR VALUE OF CORE:
Date:11.09.2023
INSTRUMENT USED
INSTRUMENT SR NO
RISHAB
2210068279
CORE -EARTH
IR VALUE 15 SEC
TEST VOLTAGE
30
500 V
CORE -YOKE
YOKE-EARTH
226.2MΩ
26.2MΩ
28.1MΩ
60 SEC
OTI (°C)
95.5KΩ
30.1MΩ
Points to be remember:
 IR testing of core is to be done at 500V & IR value should be >=1M ohm
11.LEAKAGE CURRENT :
DATE- 05/09/2023
EQUIPMENT
OLTC
BASE
VOLTAMP(MVA)
GT2
07
250
BASE VOLT
(KV)
409.0
NAMEPLATE%
IMPEDANCE
%
IMPEDANCE
15.00
15.839
%
REACTANCE
15.810
12.EARTH RESISTANCE
DATE-11.09.2023
INSTRUMENTS USED
STQC
POINT
1.
INSTRUMENTS SR NO
N156160UFV
MAIN TANK 
0.42
MB 
0.36
NEUTRAL 
0.28
LA 
R-Stru-0.41
R-Count-0.26
Y- Stru-0.40
Y-Count-0.38
B- Stru-0.33
B- Count-0.29
GENERATOR TRANSFORMER TESTING REPORT
LOCATION
GT2
13. FILTERATION DATE: 06/10/2023
14. DONE DURING OVERHAULING:
1. …SFRA DONE DATE …19/08/2023
2….FDS DONE DATE..23/08/2023
TESTING ENGINEER:
SIGN: _______________
NAME:URVASHI GAUBA
CHECKED BY:
SIGN: _______________
NAME: URVASHI GAUBA