RC-98-0014, Special Rept (Spr 970003):on 971230,declared a EDG Inoperable Due to Frequency Oscillations.Developed & Implemented Troubleshooting Plan on Electronic Governor Control Unit & Mechanical Speed Control Governor Unit

Special Rept (Spr 970003):on 971230,declared a EDG Inoperable Due to Frequency Oscillations.Developed & Implemented Troubleshooting Plan on Electronic Governor Control Unit & Mechanical Speed Control Governor Unit

ML20199H903
Person / Time
Site:	Summer
Issue date:	01/29/1998
From:	Gabe Taylor SOUTH CAROLINA ELECTRIC & GAS CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RC-98-0014, RC-98-14, SPR-970003, NUDOCS 9802050148
Download: ML20199H903 (2)

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j 4- s neunwine. sc mes twat or+anoni (803) 345-4344 SCE&O January 29,1998 RC 98 0014 Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

VIRGIL C. SUMMER NUCLEAR STATION DOCKET NO. 50/395 OPERATING LICENSE NUMBER NPF 12 SPECIAL REPORT (SPR 970003)

This Special Report is being submitted by South Carolina Electric and Gas Company (SCE&G) pursuant to the requirements of Technical Specification (TS) 4.8.1.1.3, TS 6.9.2, and Regulatory Guide 1.108, revision 1.

At 0440 hours0.00509 days <br />0.122 hours <br />7.275132e-4 weeks <br />1.6742e-4 months <br /> on December 30,1997, the "A" Emergency Diesel Generator (EDG) was declared inoperable after 8'quency oscillations were observed following the successful completion of the weekly surveillance test. Due to previous EDG test failures, the testing was being conducted in accordance with the accelerated schedule in Table 4.8-1 of the TS. During this surveillance test, the diesel started, loaded, and ran normally for the required durationi however, after the EDG was unloaded and the output breaker opened, the frequency (speed) began to oscillate significantly (58 to 62 Hz). These oscillations were observed on the frequency meter, tachometer, and fuel rack movement. An emergency start signal was initiated to place the EDG in the isochronous (emergency) mode and the oscillations, though reduced somewhat, continued. The EDG was then secured from the test.

A troubleshooting plan was developed and implemented on December 30. The troubleshooting initially focused on the electronic governor control (EGA unit), since recent problems had been encountered with this component. The EGA was removed and bench tested satisfactorily. The troubleshooting effort also focused on isolating the problem to either the EGA unit or the mechanical speed control governor (EGB unit).

However, the oscillations were erratic and intermittently repeatable, making troubleshooting difficult.

When no problems could be found on the EGA unit, the emphasis of the troubleshooting effort shifted to the EGB unit and to the input signals of the EGA unit.

Based on industry experience and vendor recommendations, the EGB unit was flushed  !

with diesel fuel and hydraulle oil to clean any contaminates and debris that may have been present.

(M i 9902050148 990129 U PDR ADOCK 05000395 i

,. Docum:nt Contrcl Desk SPR 970003 RC 98 0014

, Page.2 of 2 Following some additional troubleshooting offorts the EGB unit was replaced on January 2,1998. The EDG was loaded successfully after the component replacement, but after the breaker was opened, frequency oscillations were again observed. These oscillations were slower and cyclic, even though they were large in magnitude (55 to 63 Hz), compared to the previously observed oscillations. The unit was disassembled and inspected with the observation that there was a misalignment between the yleid link and it's connecting point with the stop lever linkage. The governor was realigned, stability adjustments were made, and tests performed to ensure that the EDG would respond within 10 seconds. The satisfactory tests confirmed that the oscillations had been caused by the EGB unit. This conclusion was further confirmed in follow up testing by the governor manufacturer where the EGB unit was found to be unstable at temperatures above 150' F (the EGB normally experiences ternperatures of 170' F).

Three confidence runs were performed after all adjustments were completed to assure the frequency oscillation problems were resolved. All test data was satisfactory and TS surveillance tests were then completed with EDG *A" declared operable at 0740 hours0.00856 days <br />0.206 hours <br />0.00122 weeks <br />2.8157e-4 months <br /> on January 5,1998. The EDG had been inoperable for 6 days and 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.

SCE&G conservatively classified the surveillance test of December 30 as a valid test and failure per Regulatory Guide 1.108 because the surveillance test was terminated before its completion even though the acceptance criteria of the surveillance was completed satisfactorily. This is the 5th failure in the last 20 valid tests and the 5th failure in the last 100 valid tests. Since EDG "A" was on an accelerated test frequency of once per 7 days in accordance with Technical Specification Table 4.31, the test schedule does not change.

Should you have any questions, please call Mr. Donald L. Jones at (803) 345 4480.

Very truly yours, SYdh 5 -c M w Gary J. Taylor GJT/dij c: J. L. Skolds G. A. Robertson W. F. Conway J. B. Knotts R. R. Mahan (w/o attachment) S. F. Fipps R. J. White INPO Records Center NRC Resident inspector RTS (SPR 980001)

L. A. Reyes File (818.08)

L, M. Padovan DMS (RC 98 0015)

NUCLEAR EXCELLENCE A SUMMER TRADITIONI

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