ML20012C263

Special Rept:On 900209,standby Diesel Generator 11 Failed. Caused by Carbonization of 3UP Relay Socket & Base Due to Short Circuit During Tightening of Lug.Relay Socket & Base Cleaned & Diesel Successfully Tested

ML20012C263
Person / Time
Site:	South Texas
Issue date:	03/09/1990
From:	Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3399, NUDOCS 9003200416
Download: ML20012C263 (3)

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l The Light c o mp a nySouth Temas Project Electric Gmrating Station P. O. Bos 289 Wadsworth, Tetas 77483 l Houston Lighting 8t Power 1

March 9. 1990 l ST-HL-AE- 3399 l I

File No.: G02 i- U. S. Nuclear Regulatory Commission Attention: Document Control Desk j Washington, DC 20555

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South Texas Project Electric Generating Station  !

Unit 1 l Docket No. STN 50-498 i Special Report Regarding l A Diesel Generator Nonvalid Failure on February 9 1990 Pursuant to the South Texas Project Electric Generating Station Technical Specifications 4.8.1.1.3 and 6.9.2, Houston Lighting & Power submits the attached Special Report regarding a diesel generator nonvalid failure which occurred on February 9, 1990.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972-8628.

CE.Yuh G. E. Vaughn % Lh%d. I Vice President Nuclear Operations BEM/n1

Attachment:

Special Report Regarding a Diesel l Generator Nonvalid Failure on February 9, 1990 l

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L i / l NL.90.059.01 A cubsidiary of Houston Industries incorporated l 90032004i6 900309 PDR ADOCK 05000498 s PDC

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.*1 ST.HL. AE. 3399 Houston Lighting & Power Company South Texas P 0 ject Electric Generating Statm, n File No.: 002 Page 2 cc:

Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 George Dick, Project Manager

~ U.'S.. Nuclear Regulatory Commission INPO

- Washington, DC 20555 Records Center 1100 circle-75 Parkway J. 1. Tapia Atlanta, CA 30339 3064 Senior Resident Inspector c/o U..S. Nuclear Regulatory Dr. Joseph M. Hendrie Commission 50 Be11 port Lane P. O. Box 910 Be11 port, NY 11713 Bay City TX 77414 D. K. Lacker J. R. Newman, Esquire., Bureau of Radiation Control Newman 6 Holtzinger, P.C. Texas Department of Health 1615 L Street, N.W. 1100 West 49th Street Washington, DC 20036 Austin, TX 78704 D. E. Ward /R. P. Verret

. Central Power & Light Company P. O. Box 2121

' Corpus Christi, TX 78403 J. C. Lanier Director of Generation City of Austin Electric Utility 721 Barton Springs Road Austin, TX 178704 R. J. Costello/M T. Hardt City Public Service Board P. O. Box 1771 San Antonio, TX 78296 Revised 12/15/89 L4/NRC/

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Attachment ST-HL-AE- 3399 ,

Page 1 of 1 South Texas Project Electric Generating Station i, Unit 1 Docket No STN 50-498 Special Report Regarding A Nonvalid )

Failure of #11 Standby Diesel Generator on February 9, 1990 s i  !

DESCRIPTION OF EVENT:

1 On February 9, 1990, Unit I was in Mode 1 at 100 percent power. At 1445 j hours Standby Diesel Generator 11 was started to satisfy Technical i Specification surveillance requirements. It was then paralleled with offsite power and loaded for approximately 55 minutes. .At that time reactive load dropped from 4125 kVARs to 600 kVARs. The reactive power was adjusted back to I

4200 kVARs, however, within approximately two minutes the kVAR noter pegged high and then indicated negative retStive power. The generator output breaker automatically tripped on reverse power and the test was terminated.

Troubleshooting of the voltage regulator was performed to determine the  ;

cause of the failure. Some carbonization was found in the socket of relay 3UP 1 which may have caused it to spuriously operate resulting in erratic voltage ,

regulator response. The carbonization was the result of a short circuit arc l which occurred during the tightening of a lug on the socket of the relay ,

earlier that day. The adjacent circuitry was checked for damage following the- i short circuit; however, the carbonization inside the relay socket was not noticed. The relay socket and base were cleaned and SDG 11 was successfully tested at 0538 hours0.00623 days <br />0.149 hours <br />8.895503e-4 weeks <br />2.04709e-4 months <br />'on February 10, 1990.

CAUSE OF EVENT:

The cause of this nonvalid failure was carbonization of the 3UF relay socket and base due to an inadvertent short circuit during the tightening of a lug.

CORRECTIVE ACTION:

The 3UP relay socket and base were cleaned and the diesel was successfully tested.

ADDITIONAL INFORMATION:

Per the criteria of Regulatory Guide 1.108, the failure described herein has been classified as a nonvalid failure. There have been a total of 55 valid tests of SDG 11 since the completion of the diesel generator reliability demonstration. As such, the test interval for SDG 11 remains at once per 31 days.

NL.90.059.01