In the course of repairing a defect in the oil line of auxiliary house transformer the latter was tripped by protection. The unit was shut down. The cause of protection actuation was personnel error. Six hours later while starting RCP-1 short-circuit in the 6 kV breaker cabinet of this pump has occurred due to loss of contact in the breaker phase. The resulting smoke was extinguished by operating personnel in 15 minutes. After replacement of the damaged breaker on 2.6.91 the unit was raised to the minimum controlled power level.
BASIS FOR RATING: Initiator - actuation of transformer protection due to personnel error.
Criterion - degradation of defence-in-depth. Initiating event, real, expected. Safety function availability - full, which corresponds to level 0/1 (A-1R). Since the event cause shows deficiencies in the safety culture the maximum level has been chosen according to 4.2b.
DIFFICULTIES IN RATING:
Event date: Sat, 01-06-1991