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Tuesday, July 19, 2011

Autotripping of 50MVA Transformer due to Earthquake

We had experienced a shallow earthquake which caused the tripping of our 50MVA Transformer. Below is the incident report of the tripping:

I. BACKGROUND OF THE PROBLEM:
July 7, 2011
0659H-Strong shallow earthquake (4.3 magnitude) hit
- 50 MVA Transformer at Substation autotripped (115kV circuit breakers)
Indications:
* Transformer Buchholtz/Surge Tripped
* OLTC Oil Level Alarm
Note:
• 69kV feeder breakers autotripped due to actuation of UFR (BBC Circuit Shield)

II. ACTIONS TAKEN
0700H-Informed concerned officials about the tripping (Dispatcher, District Manager and Chief Supervisor)
0705H- Conducted visual inspection on the 50 MVA Transformer and the affected breakers
-Transformer and OLTC Conservator Oil Levels are normal
-115, 69 kV and Neutral bushings of the 50 MVA Transformer are normal. No cracks and oil leaks was found.
-Observed physical appearance of the Transformer and no deformity was seen.
-69kV Breakers are all in normal condition.
- released the accumulated gas on the bleeder of Buchholtz Relay
0720H- Received energization clearance from District Manager, Chief Supervisor, Test Manager
0722H- Manually tripped the remaining 69kV feeder breaker without UFR upon advice of Dispatcher
- successfully closed 115kV breaker 1 via SCADA
0723H- Successfully closed 115kV Breaker 2 via SCADA
0725H- Successfully energized the three 69kV feeder breakers

III. ROOT CAUSE OF THE PROBLEM
Oil was disturbed from the main tank due to strong shallow earthquake. The abrupt shaking of the ground produced gas that trips the Buchholtz relay of the power transformer.

IV. RECOMMENDED ACTION PLAN
1. Report immediately to concerned officials to minimize outage duration

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