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At 1655 on April 6, 2005, a trip of the 4A … At 1655 on April 6, 2005, a trip of the 4A/4B Transformer occurred at Limerick Generating Station in the 500 KV Substation. This de-energized one of the required off site sources and the associated 20 Start-up Bus and 201 Safeguard Bus, causing a valid actuation signal for the D12, D14, D21, and D23 Diesel Generators. All Diesels started and their associated 4 KV buses swapped to the 101 Safeguard Bus as required. Cause of the 4A/4B Transformer trip is under investigation. Power reduction on Unit 2 was performed in response to lowering Main Condenser vacuum during power supply transfers. Condition was stabilized and Unit 2 Reactor power restored to 100 %.</br>The cause of the lowering main condenser vacuum was that when the bus transfer occurred, several air valves on Unit 2 cycled which caused the lowering vacuum. Once power transferred, Unit 2 stabilized and was restored to 100% power. Unit 1 main condenser vacuum was not affected since power was not transferred on Unit 1.</br>Additionally, a Group 6A valve isolation signal was generated. This caused the purge valves to receive an isolation signal but the purge valves were not in operation nor were they required to be in operation at the time of the isolation signal. Both unit's Reactor Water Clean-up (RWCU) pumps tripped due to the isolation signal. At the time of this report, the isolation signal was reset, Unit 1 RWCU pump has been reset, and preparations are being made to restart Unit 2 RWCU pump.</br>The only other anomaly is that Unit 2 D22 diesel is in a maintenance outage and is scheduled to be returned to service tomorrow.</br>Currently, both units are in a 72-hour LCO action statement due to loss of one offsite power supply.</br>The licensee will inform the NRC resident inspector.ee will inform the NRC resident inspector. +
21:55:00, 6 April 2005 +
41,573 +
22:56:00, 6 April 2005 +
21:55:00, 6 April 2005 +
At 1655 on April 6, 2005, a trip of the 4A … At 1655 on April 6, 2005, a trip of the 4A/4B Transformer occurred at Limerick Generating Station in the 500 KV Substation. This de-energized one of the required off site sources and the associated 20 Start-up Bus and 201 Safeguard Bus, causing a valid actuation signal for the D12, D14, D21, and D23 Diesel Generators. All Diesels started and their associated 4 KV buses swapped to the 101 Safeguard Bus as required. Cause of the 4A/4B Transformer trip is under investigation. Power reduction on Unit 2 was performed in response to lowering Main Condenser vacuum during power supply transfers. Condition was stabilized and Unit 2 Reactor power restored to 100 %.</br>The cause of the lowering main condenser vacuum was that when the bus transfer occurred, several air valves on Unit 2 cycled which caused the lowering vacuum. Once power transferred, Unit 2 stabilized and was restored to 100% power. Unit 1 main condenser vacuum was not affected since power was not transferred on Unit 1.</br>Additionally, a Group 6A valve isolation signal was generated. This caused the purge valves to receive an isolation signal but the purge valves were not in operation nor were they required to be in operation at the time of the isolation signal. Both unit's Reactor Water Clean-up (RWCU) pumps tripped due to the isolation signal. At the time of this report, the isolation signal was reset, Unit 1 RWCU pump has been reset, and preparations are being made to restart Unit 2 RWCU pump.</br>The only other anomaly is that Unit 2 D22 diesel is in a maintenance outage and is scheduled to be returned to service tomorrow.</br>Currently, both units are in a 72-hour LCO action statement due to loss of one offsite power supply.</br>The licensee will inform the NRC resident inspector.ee will inform the NRC resident inspector. +
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