ML20084F608

AO 250-75-3:on 750517,battery Charger Transformer 3A Failed. Caused by Unsatisfactory Original Insulation.Transformer Replaced.Vendor Examined Failed Transformer & Repaired Charger.Charger 3A Placed Back in Svc

ML20084F608
Person / Time
Site:	Turkey Point
Issue date:	05/27/1975
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Rusche B Office of Nuclear Reactor Regulation
References
AO-250-75-3, NUDOCS 8304210186
Download: ML20084F608 (2)

Text

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Mr. Benard C. Rusche, Director fi J_e$ '

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Dear Mr. Rusche:

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-f ABNORMAL OCCURRENCE 250-75-3 Y TURKEY POINT PLANT UNIT 3 UATE OF OCCURRENCE: MAY 17, 1975 3A BATTERY CHARGER TRANSFORMER FAILURE A. CONDITIONS PRIOR TO OCCURRENCE Unit 3 was in normal operation at full load. The 3A battery charger was in service at about 50-55% of rated output supplying the 3A battery bus.

B. DESCRIPTION OF OCCURRENCE About noon on May 17, 1975, smoke was observed coming from the 3A battery charger and the smoke and fire detection alarm sounded in the Control Room. It was determined that one of the transformers was overheating which caused the smoke.

C. CAUSE OF THE OCCURRENCE The failed transformer was determined to have the original insulation which was not satisfactory. All of the transformers with the original insulation were thought to have been changed out in 1973 as a result of Abnormal' Occurrence 3-72-8 (see Failure Data).

D. ANALYSIS OF THE OCCURRENCE The health and safety of the public was not affected by the battery charger failure because service was not interrupted to the DC system. Even with no charger in service on.the 3A DC Bus, the 3A battery could have supplied all DC accident loads on the 3A bus for more than 30 minutes if the design basis accident had occurred at the time of the charger failure. Manually placing the 3S charger in service in lieu of the 3A charger restored the system to normal.

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Mr. Benard C. Rusche, Director .

Page Two May 27, 1975 E. CORRECTIVE ACTION

1. Immediate The charger was' manually isolated promptly after the failure.

The 3S battery charger was placed in service to replace the 3A charger. The 3A charger was visually examined and the transformer was found to be the source of the smoke. The transformer was replaced with a transformer having a Class F insulation and a vendor representative was requested to examine the charger prior to returning it to service.

2. Permanent The vendor representative examined the failed transformer and the repaired 3A charger both while isolated and while under load. Based on his recommendations, the charger was placed back in service. The insulation in 3S and 3B battery charger transformers will be verified to be correct.

F. FAILURE DATA A similar failure occurred on December 16, 1972. This was reported-as Abnormal Occurrence 3-72-8.

Very truly yours, A. D. Schmidt Vice President Power Resources GEL /cpc cc: Mr. Norman C. Moseley Jack R. Newman, Esquire l

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