ML20127K693

Ro:On 730909,number 6 Transformer Protective Relaying Initiated an Automatic Trip.Caused by Pinched Wire That Shorted Current Transformer.Wire Repaired & Sys Returned to Normal

ML20127K693
Person / Time
Site:	Monticello
Issue date:	09/18/1973
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9211200475
Download: ML20127K693 (1)

Text

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NSD NORTHERN STATES POWER COMPANY Minneapolis, Minnesota 55401

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September 18, 1973 ,

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4 Mr. J. F. O' Leary, Director Directorate of Licensing -h f'kg/ v 1 \

p United States Atomic. gy Conunission F. - /".? '/ H Washington, D. C. 20.

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Dear Mr. O' Leary:

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FKNflCEllD NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Temporary Loss of No. lAR Transformer A coindition occurred at the Monticello Nuclear Generating Plant which we are E reporting to your office in accordance with Section 6.7.B.1, Abnomal Occurrence Reports, of the Technical Specifications, of Provisional Operating License DPR-22.

On September 9,1973, operation of the No. 6 transfomer protective relaying initiated an automatic trip of the No. lAR reserve transfomer primary breaker.

The No. 6 transf: :mer was then isolated and the No. lAR transfomer was re-energized. The m. lAR transformer is a redundant source of off-site power for the plant safeguards busses. The No lAR transformer was deenergized for a period of approximately 29 minutes.

Investigation revealed that the cause of the relay operation was a pinched wire which shorted the No. 6 transformer A phase current transformer. The wire wa repaired and the No, 6 transfoncer was returned to service. Wiring for the current transfomers for the other two phases of No. 6 transfomer was inspected and found to be proper.

The occurrence did not affect safe operation of the plant since the No. IR startup transformer and both diesel generators were operable during the time that the No. lAR transformer was de-energized. At the time of the occurreace the station auxiliary power was being supplied by the #11 station auxiliary transfomer. No previous losses of the No lAR transfomer have occurred due to inadvertent protective relay operations.

Yours very truly, 40 11 y %p g Director of Nuclear Support Services j /pg -

IOVHmin 9211200475 730918 PDR

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S ADOCK 05000263 i PDR 4 cc: J G Keppler 9, G Charnoff L'

\g Minnesota Pollution Control Agency Ken Dzugan ATTN:

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