During normal operation unit power reduction occurred on the tripping of one of the two operating TGs due to short circuit in the voltage regulator of the auxiliary power transformer followed by the burning of oil, which leaked out of the transformer. The fire was extinguished by the fire-figthing system assisted by the plant fire brigade. 13 hours after the event the nominal power was restored. Breach of safe operation limits and conditions did not occur.
BASIS FOR RATING: Initiator - short circuit.
Criterion - degradation of defence-in-depth.
Initial event - expected, real. Safety function availability: full, which corresponds to level 0/1 (A-1R).
DIFFICULTIES IN RATING:
Event date: Thu, 28-03-1991