ML20028H844

Special Rept SR-90-004-00:on 901226,emergency Diesel Generator Tripped on Loss of Field While Operating at 100% Power.Caused by Faulty Motor Operated Potentiometer.Faulty Component Replaced

ML20028H844
Person / Time
Site:	Waterford
Issue date:	01/25/1991
From:	Mcgaha J ENTERGY OPERATIONS, INC.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
SR-90-004-00, SR-90-4, W3B5-91-0046, W3B5-91-46, NUDOCS 9101300284
Download: ML20028H844 (4)

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7 W3B5-91-0046 A4.05 QA January 25, 1991 U.S. Nuclear Regulatory Commission ATTENTION: Document Control Desk Washington, D.C. 20555

SUBJECT:

Waterford 3 SES Docket No. 50-382 License No. NPF-38 Reportina of Special Report Gentlemen:

Attached is Special Report Number SR-90-004-00 for Waterford Steam Electric Station Unit 3. This Special Report is submitted por 10CFR50.36(c)(2) and Technical Specifications 4.8.1.1.3 and 6.9.2.

Very truly yours,

,J.R. McGaha General Manager Plant Operations JRM/DDW:glp Attachment cc: Messrs. R.D. Martin G.L. Florreich J.T. Wheelock - INPO Records Center E.L. Blake D.L. Wigginton NRC Resident Inspectors Office sElg2sggOCK05ooo3g2 284 91012s ili

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l SPECIAL REPORT S R-90-004- 00 Valid failure of Emergency Diesel Generator 'B'.due to faulty operation of the voltage regulator motor operated potentiometer.

INTRODUCTION On December 26, 1930, k'aterford Steam Electric Station Unit 3 was operating at

. 100% power when Emergency Diesel Generator (EDG) 'B' tripped on a loss of field. The EDG was being unloaded after completing the rapid loading test portion of " Emergency Diesel Generator Operability Verification Procedure,"

Operating Frocedure OP-903-068. This event has been classified as a valid failure.

The root cause of this event was a faulty motor operated potentiometer (MOP) in the voltage regulator. Erratic output from the MOP resulted in fluctuations in generator excitation causing load surging and eventual tripping of the EDG by the loss of field protective relay during EDO unloading. There was no hazard to plant equipment or the health and safety of the general public, s

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9 NARRATIVE At 1731 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.586455e-4 months <br /> on December 26, 1990, Waterford Steam Electric Station Unit 3 was operating at 100% power when Energency Diesel Generator (EDG) (EIIS Identifier EE-ENG) 'B' tripped on loss of field when being unloaded after compitaing the rapid loading test portion of " Emergency Diesel Generator 1' Operability Verification Procedure " Operating Procedure (OP) 903-068.

OP-903-068 was commenced at 1625 for the timed loading tent to satisfy Technteni Specification (TS) 4.8.1.1.2.a.S. At 1627. EDG 'B' 'and been loaded to greater than 4200 kilowatts (KW) in 141.34 seconds, satisfactorily corricting TS 4.8.1.1.2.c.5 requirements. During EDG 'B' unloading, with EDG output at 2.2 megawatts and 270 amperes, EDG current increased rapidly and negawatt and megavar output slowly increased. At 1731 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.586455e-4 months <br />, the EDG output breaker (EIIS Identifier BKR) tripped on loss of field when EDG current reached 600 amperes. The loss of field relay (EIIS Identifier 40) is bypassed when the EDC is in the emergency mode.

At 1748 EDG 'B' was started for troubleshooting. EDG 'll' was agath successfully loaded to greater than 4200 KW and once again tripped on loss of field during unloading, when EDG current rapidly rose to 600 amperes.

The root cause of this event was a faulty motor operated potentiometer (MOP) in the voltage regulator (E11S Identifier RG)- Erratic output from the MOP resulted in fluctuations in generator excitat.on. These fluctuations in excitation produced load surging that was significant during unloading, causing the loss of field protective relay to trip the EDC. Although the fnuity MOP did not prevent satisfactory full loading of-EDG 'B', this event is being classified as a valid failure because the faulty MOP could have possibly i

prevented required loading of the EDG while in the emerger.ty mode.

'nats f ailure is the first f ailure' dur.ing a valid test of EDG 'B' at Waterford 3 since the operating license was issued. There has also been one failure during a valid test of EDG 'A'. EDG 'B' was declared inoperable at 1731 on December .

26, 1990. The faulty component, the MOP, was replaced and EDO 'B' was tested satisfactorily and declared operable at 2153 on December 28, 1990. The current

- surveillance. test interval is at least once per 31 days, which is in conformance with the schedule of Regulatory position C.2.d. of Reguintory Guide 1.108. This event did not present a hazard to plant equipment or the health and safety of the general public.

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j i PLANT CONTACT i

- T.11. Smith, Plant Engineering Superintendent, $04/464-3127 i

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