ML20237C905

Ro:On 871105,diesel Generator 2A Inoperable for 22 H.Caused by Dirty Voltage Range & Adjustment Potentiometer (Pot) in Voltage Regulator.Pot Cleaned & Exercised Through Full Range

ML20237C905
Person / Time
Site:	Byron
Issue date:	12/03/1987
From:	Querio R COMMONWEALTH EDISON CO.
To:	Davis A NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
BYRON-87-1165, NUDOCS 8712220249
Download: ML20237C905 (2)

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PAD DL(.$g,:a, e Mr. A. Bert Davis Regional Administrator Region 3 U.S. Regulatory Commission 799 Roosevelt Road Glenn Ellyn, Illinois 60137

Dear Sir:

This report is submitted in accordance with Byron Station Unit 2 Operating License NPF-60 Appendix A, Technical Specification 4.8.1.1.3, reporting of j Diesel Generator Failures. i I

This report addresses two nonvalid tests and failures experienced on the 2A diesel generator. The criteria to determine valid tests and failures is in accordance with Section C.2.e of Regulatory Guide 1.108.

On November 5, 1987 at 0956 the 2A diesel generator (DG) was started per the Monthly Operability Surveillance, 2BOS 8.1.1.2.a-l. Approximately twenty l minutes into the full load run the engine operator noticed several large kilo voltage-ampere reactive (KVAR) swings. The 2A DG was unloaded, shutdown and Limiting Condition for Operation Action Requirement (LCOAR) 2BOS 8..l.1-la was entered for one diesel generator inoperable. Following several conversations j with the voltage regulator specialists at the Commonwealth Edison Tech Center,  !

and the Load Dispatcher, it was decided to restart the 2A DG for a maintenance run. The Tech Center Personnel theorized that the KVAR swings may have been induced by an unstable grid. At 1356 the 2A DG was started and synchronized to the grid. The 2A DG was operated with no abnormalities for seventy four minutes. Based on the successful maintenance run, the 2A DG was restarted, at 1556, per the Monthly Operability Surveillance. Fifty six minutes into the  ;

full load run the engine operator noticed another large KVAR swing. At 1710 l the engine was shutdown. Tech Center personnel were contacted and brought to '

the site to assist in the investigation. Following two troubleshooting runs  !

the root cause was determie d, and corrective action was taken. At 0305 on l November 6, 1987 the 2A DG was restarted per the Monthly Operability Surveillance. At 0541 the Surveillance was successfully completed. 140AR 2BOS 8.1.1-la was exited at 0830 on November 6, 1987. .

l The root cause for these two events was a dirty voltage range and adjustment potentiometer (POT) in the voltage regulator. The source of the dirt is most likely an accumulation from construction activities in the general area. The effect of the dirty POT was an erratic voltage control signal from the voltage regulator to the diesel generator exciter. With the DG synchronized to the grid (Test Mode), this condition created the large KVAR swings. The faulty POT Q2220249g71203 I o g ADOCK 05000455 "a DEC10 m g p w

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would have had minimal effect on the 2A DG in the emergency mode. Minor voltage swings may have occurred, however, due to the total possible range adjustment on the POT, no voltage swings could have occurred outside the L- Technical Specification limits of + or - 420 volts. Per Section C.2.a.2 of Regulatory Guide 1.108 these two failures are considered nonvalid tests and i failures.

l l The faulty POT was cleaned with contact cleaner and exercised through its full range. Another POT with a similar function was also cleaned and exercised.

These corrective actions will also be performed on the 1A, 1B, and 2B DG's.

AIRS 454-512-87-0287, and 455-512-87-0288 will track the completion of this work for Unit One and Unit Two respectively. 1 I

The 2A diesel generator was inoperable for twenty.two hours during this event. The testing frequency for the 2A DG will remain on a monthly bacis ac nonvalid failures do not affect the testing frequency. The 2A DG has completed forty two consecutive valid tests without a valid failure.

b$t.L R. E. Querio Station Manager l Byron Nuclear. Power Station' .

REQ /MMR/JC/bf (0179z) cc: P. Brochman, NRC Senior Resident Inspector U.S. NRC Document Control Desk, Washington, D.C.

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