WHAT CAUSED THE FAILURES OF THE WESTINGHOUSE TYPE AR RELAYS

摘要

On March 29,1999, during the sixth refueling outage at Seabrook Station, the "B" Train Emergency Diesel Generator (EDG) failed its 18 month, Technical Specification loss of off-site power test. The test failure occurred when a Westinghouse Type AR high speed, auxiliary relay in the Emergency Power Sequencer (EPS) failed to function properly. The function of this relay was to open the 4160 volt circuit breaker that connects the Unit Auxiliary Transformer (UAT) to the Emergency Bus. As a result of this relay failure, the Emergency Diesel Generator started but its output breaker did not close thus preventing the EDG from energizing the emergency bus during testing. After replacing the failed relay, the EDG loss of power test was resumed and another EPS Westinghouse Type AR high speed, auxiliary relay that performed a different function, failed to operate properly. This relay was designed to start the Containment Building Spray (CBS) pump. While the emergency bus was successfully energized, this relay failure prevented the CBS pump from starting automatically. This paper describes the two events associated with the failures of two Westinghouse AR relays. This paper also describes the electrical laboratory testing, chemical analyses and the root cause analysis which were performed to determine the root cause of the failures of the two Westinghouse AR relays.