Page 25 - ECLECTIC MARCH-2022 INSIDE PAGES_p2.indd
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le 1: DGA Results 15/02/19 19/05/19 22/05/19 24/05/19 24/05/19
After trip-ping Before ltration) (Before recommissioning) (After tripping)
Gas 35
15 694 122 79 70
H2 (Hydrogen) 198 70 41 32
CH4 (Methane) 1 6
C2H6 (Ethane) 40 12 3 3
C2H4 (Ethylene) 30 378 174 94 80
C2H2 (Acetylene) 124 371 86 83 48
CO2 (Carbon Dioxide) 10 3923 756 426
CO (Carbon monoxide) 255 447 1335 32 16
Total 6023 70 1088 675
1863
subsequently, DGA test was carried out for the above by removing the diverter switch from the diverter
transformer with satisfactory results. (Refer Table- I) tank and then 30 kV DC was applied between the
➤ Clearance for charging the transformer was given at phases through HT bushings. Although the results
tap no.-5 only. were found satisfactory for R-B & Y-B, the high
➤ It was charged subsequently from low voltage side at voltage could not be applied across R-Y phases due
11:55 am on 24/05/2019 and the transformer tripped to increase in leakage current appreciably. This result
almost immediately at 11:56 am on 24/05/2019. clearly signified a very low insulation resistance fault
between Red & Yellow phases.
TRIP - 3 Again the oil was drained out from the main tank and
during subsequent inspection, the following damages
Date & Time of Fault: 11:56 am on 24/05/2019 were identified:
➤ Four numbers of Hylam bar make supports, holding
Relay Operation: the tap leads were found to be faulty. (As shown in
1. Differential Relay Figure 1)
2. Main Tank Buchholz Relay
3. Main Tank PRV relay. Figure 1: Flashover At The Hylam Bar, Holding the
4. Master trip relay (both HV & LV) and Tap Leads
5. NIDS (Nitrogen Injection Drain and Stir) system
operated.
Details of Fault and its subsequent action for
restoration:
➤ On this occasion, it was analyzed from the relay
operation that as if a three phase short circuit fault
had developed at the 132 kV windings for the power
transformer.
➤ On all of the earlier occasions, pressure test was
carried out on the windings with respect to earth.
But the pressure test could not be carried out
between the phases due to the existing neutral
formation at the tap changer. So, it was decided to
isolate all the three phases of the 132 kV windings
25
After trip-ping Before ltration) (Before recommissioning) (After tripping)
Gas 35
15 694 122 79 70
H2 (Hydrogen) 198 70 41 32
CH4 (Methane) 1 6
C2H6 (Ethane) 40 12 3 3
C2H4 (Ethylene) 30 378 174 94 80
C2H2 (Acetylene) 124 371 86 83 48
CO2 (Carbon Dioxide) 10 3923 756 426
CO (Carbon monoxide) 255 447 1335 32 16
Total 6023 70 1088 675
1863
subsequently, DGA test was carried out for the above by removing the diverter switch from the diverter
transformer with satisfactory results. (Refer Table- I) tank and then 30 kV DC was applied between the
➤ Clearance for charging the transformer was given at phases through HT bushings. Although the results
tap no.-5 only. were found satisfactory for R-B & Y-B, the high
➤ It was charged subsequently from low voltage side at voltage could not be applied across R-Y phases due
11:55 am on 24/05/2019 and the transformer tripped to increase in leakage current appreciably. This result
almost immediately at 11:56 am on 24/05/2019. clearly signified a very low insulation resistance fault
between Red & Yellow phases.
TRIP - 3 Again the oil was drained out from the main tank and
during subsequent inspection, the following damages
Date & Time of Fault: 11:56 am on 24/05/2019 were identified:
➤ Four numbers of Hylam bar make supports, holding
Relay Operation: the tap leads were found to be faulty. (As shown in
1. Differential Relay Figure 1)
2. Main Tank Buchholz Relay
3. Main Tank PRV relay. Figure 1: Flashover At The Hylam Bar, Holding the
4. Master trip relay (both HV & LV) and Tap Leads
5. NIDS (Nitrogen Injection Drain and Stir) system
operated.
Details of Fault and its subsequent action for
restoration:
➤ On this occasion, it was analyzed from the relay
operation that as if a three phase short circuit fault
had developed at the 132 kV windings for the power
transformer.
➤ On all of the earlier occasions, pressure test was
carried out on the windings with respect to earth.
But the pressure test could not be carried out
between the phases due to the existing neutral
formation at the tap changer. So, it was decided to
isolate all the three phases of the 132 kV windings
25
