ML20210V321

Special Rept Spr 86-013:on 860907,during Surveillance Testing Emergency Diesel Generator B Declared Inoperable Due to Loss of Voltage Control.Caused by Loose Screw in Coupling of motor-operated Potentiometer

ML20210V321
Person / Time
Site:	Summer
Issue date:	09/25/1986
From:	Nauman D SOUTH CAROLINA ELECTRIC & GAS CO.
To:	Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
SPR-86-013, SPR-86-13, NUDOCS 8610100666
Download: ML20210V321 (2)

Text

r soge A. mn o gna Electric & Gas Company umbi 29218 Nuclear Operabons

, SCE&G

~~

September 25, 1986 El A?

a

'N f.c Dr.'J. Nelson Grace na Regional Administrator --

U. S. Nuclear Regulatory Commission **

Suite 2900 m 101 Marietta Street, NW "

Atlanta, Georgia 30323

SUBJECT:

Virgil C. Summer Nuclear Station Docket No. 50/395 Operating License No. NPF-12 Special Report (SPR 86-013)

Dear Dr. Grace:

Attached is a Special Report for the Virgil C. Summer Nuclear Station.

This Special Report is submitted pursuant to the requirements of Section 6 of the Technical Specifications and Regulatory Guide 1.108.

Should there be any questions, please call us at your convenience.

ry ul y urs, s

o. . u kn RJB: DAN /bjh Attachment cc: 0. W. Dixon, Jr./T. C. Nichols, Jr. K. E. Nodland E. H. Crews, Jr. R. A. Stough E. C. Roberts G. O. Percival J. G. Connelly, Jr. R. L. Prevatte W. A. Williams, Jr. J. B. Knotts, Jr.

Group Managers S. D. Hogge

0. S. Bradham I&E Washington D. R. Moore Document Management C. A. Price Branch G. G. Soult INP0 Records Center W. T. Frady ANI Library C. L. Ligon (NSRC) NPCF R. M. Campbell File b

~

8610100666 860925 PDR ADOCK 05000395 S PDR Il

.s

'- Dr. J. Nelson Grace

! SPR 86-013 Page Two l September 25, 1986 EVENT DESCRIPTION On September 7, 1986, at 0530 hours0.00613 days <br />0.147 hours <br />8.763227e-4 weeks <br />2.01665e-4 months <br />, Emergency Diesel Generator (EDG) "B" was declared inoperable during scheduled surveillance testing due to the loss of voltage control in the Test Start Mode. As part of the test, the unit had been successfully started in the Emergency Start Mode. In the Emergency Start Mode, voltage control is bypassed; therefore, to

! facilitate paralleling and loading of the unit during testing, the unit is placed in the Test Start Mode providing the operator with voltage control. After the unit was placed into the Test Start Mode and failed to respond to an input, the operator declared the unit inoperable, initiated a Maintenance Work Request (MWR) for repair, and EDG "A" was verified to be operable as required by the Technical Specifications.

i Investigation by Maintenance electricians identified the cause of this

] event to be a loose set screw in the coupling of the motor operated potentiometer. This allowed the drive shaft of the motor to rotate in i the coupling, thereby failing to drive through to the potentiometer. The i set screw was tightened, the voltage regulator limits adjusted and the i unit was satisfactorily tested and declared operable September 7, 1986, I

at 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br />.

The loss of voltage control in the Test Start Mode is classified as a

- non-valid failure as determined by the criteria set forth in Regulatory i Guide 1.108, " Periodic Testing of Diesel Generator Units." The units i Emergency Start Mode voltage is established at 7200V, +2 -5 percent (6840-7344) and is verified during testing. The unit voltage on the initiation of the Emergency Start during this test was 6900V and as such would have performed its designed function. During an Emergency Start voltage control is bypassed and voltage is maintained by isochronous

operation.

CONCLUSION Emergency Diesel Generator "B" has had two valid test failures in the last one hundred valid tests, one valid test failure in the last twenty valid tests and is presently being tested once per 31 days.

1 i

- . . - __ . - - _ _ . -_ .._.._ _._- - _.-_ -.- _