ST-HL-AE-2623, Special Rept:On 880316,nonvalid Failure of Standby Diesel Generator 13 Occurred While Performing Operability Surveillance Testing.Engineering Evaluation Initiated to Consider Mods to Relay Circuitry.Rept Expected by 880701

Special Rept:On 880316,nonvalid Failure of Standby Diesel Generator 13 Occurred While Performing Operability Surveillance Testing.Engineering Evaluation Initiated to Consider Mods to Relay Circuitry.Rept Expected by 880701

ML20151K509
Person / Time
Site:	South Texas
Issue date:	04/15/1988
From:	Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
ST-HL-AE-2623, NUDOCS 8804210332
Download: ML20151K509 (4)

Text

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C The Light company P.O. Box 1700 liouston, Texas 770u1 (713) 228 9211 Ifouston Lighting & Power . - - ~ - - - - - - - - - - - . -

April 15, 1988 ST-HL-AE-2623 File No.: G02 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 i

South Texas Project Electric Generating Station Unit 1 Docket No. STN 50-498 Special Report Regarding a Nonvalid Failure of #13 Standby Diesel Generator

Reference:

Letter ST-HL-AE-2489 dated January 28, 1988 from G. E. Vaughn to the NRC.

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 nonvislid failure of the #13 Standby Diesel Generator. A similar event occurred and is documented in the referenced letter. A supplemental report will be submitted by July 1, 1988.

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

G. E. Vaughn l Vice President Nuclear Plant Operations GEV/CAA/cir l

j Attachmant: Special Report Regarding a l Nonvalid Failure of #13 Standby Diesel Generator 8804210332 880415 r

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PDR ADOCK 05000498 S DCD i\

l A Subsidiary of Ilouston Industries incorporated NL.88.104.01

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.,. .s Ifouston Lighting & Power Company ST-HL-AE-2623 File No.: G02 Page 2~

cc Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associated General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 1700 Houston, TX 77001 N. Prasad Kadambi, Project Manager U. S. Nuclear Regulatory Commission INPO 1 White Flint North Records Center 11555 Rockville Pike 1100 Circle 75 Parkway Rockville, MD 20859 Atlanta, Ga. 30339-3064 Dan R. Carpenter Dr. Joseph M. Hendrie Senior Resident Inspector / Operations 50 Be11 port Lane c/o U. S. Nuclear Regulatory Commission Bellport, NY 11713 P. O. Box 910 Bay City, TX 77414 Don L. Garrison Resident Inspector / Construction c/o U. S. Nuclear Reeulatory Commission P. O. Box 910 Bay City, TX 77414 J. R. Newman, Esquire Newcan & Holtzinger, P.C.

1615 L Street, N.W.

Washington, DC 20036 R. L. Range /R. P. Verret Central Power & Light Company P. O. Box 2121 Corpus Christi, TX 78403 R. John Miner (2 copies)

Chief Operating Officer City of Austin Electric Utility 721 Barton Springs Road Austin, TX 78704 R. J. Costello/M. T. Hardt l

City Public Service Board i P. O. Lox 1771

[ San Antonio, TX 78296 I

Revised 03/18/88 NL.DIST l j l

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4 Attachment ST-HL-AE-2623 Page 1 of 2 South Texas Project Electric Generating Station Unit 1 Docket No. STN 50-498 Special Report Regarding a Nonvalid Failure of #13 Standby Diesel Generator DESCRIPTION OF EVENTS:

A nonvalid failure occurred while performing operability surveillance testing on Standby Diesel Generator (SDG) #13 on March 16, 1988.

At approximately 0448 CST on March 16, 1988 a nonvalid failure occurred during loading cf SDG #13 with the SDG unit operating in parallel with offsite power.

Following a successful start the operator paralleled the unit with offsite power and began adding load. At approximately 90% full load the instantaneous directional overcurrent relay (67/50H) operated tripping the SDG output breaker. The SDG successfully handled the near full load rejection and continued operating at rated voltage. The surveillance test was terminated pending investigation of the relay actuation.

The SDG output current at the time of the trip was approximately 700 Amps with a portion of this current supplying the loads of 4.16KV switchgear E1C and the remainder flowing back into the system through the current transformer of the 67/50H Relay. The operating setpoint of the 67/50H Relay is 1008 Amps.

Based on the SDG output current being well balov the operating.setpoint of the relay and the investigation of a recent similar event on SDG #11 (Refer to letter ST-HL-AE-2489 dated January 28, 1988), instrumentation was connected to the 67/50E Relay to monitor its operating parameters and the operability-surveillance test was repeated.

l l The SDG #13 operability surveillance was completed satisfactorily at 0025 on March 17, 1988. The unit was started, paralleled with offsite power, and operated under full load conditions for a minimum of one hour in accordance with surveillance requirements.

It is noted that actuation of the 67/50H Relay would not have prevented the E

SDG from performing its safety function. The SDG cannot be paralleled while a a Safety Injection (SI) signal is present. The SDG's are paralleled with offsite power during performance of the monthly operability surveillance in l order to satisfy the full load test requirement. The 67/50H relay requires current flow back into the system to be operational, which requires parallel operation of the SDG with offsite power.

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Attachment ST-HL-AE-2623 Page 2 of 2 The SDG remained operable and was available to perform its safety function throughout the event.

ROOT CAUSE:

The nonvalid failure has been attributed to a spurious actuation of the instantaneous directional overcurrent relay. Permanent plant instrumentation has verified that the current as seen by the relay was well below its operating setpoint. Discussions with the relay manufacturer following a similar eventoon SDG #11 revealed that a transient on the D.C. supply voltage to the relay might cause an inadvertent actuation. A review of the relay application and setpoint performed prior to the event confirmed that the relay

-was properly applied and set.

A supplemental report will be submitted by July 1, 1988 following tho'results of the actions discussed below.

CORRECTIVE ACTION:

The following corrective actions are being taken:

1. An engineering evaluation has been initiated to consider modifications to the 67/50H relay circuitry to avoid spurious actuations. The evaluation will be completed by June 1, 1988.

2. Instrumentation will be connected to_the 67/50H relay to monitor A.C.

current and D.C. voltage parameters during performance of the monthly operability surveillance tests on each SDG.

ADDITIONAL INFORMATION:

Per the criteria of Regulatory Guide 1.108 the failure described in this report has been classified as a nonvalid failure. As such, the current test interval for SDG #13 remains 31 days. There have been fourteen (14) valid tests performed on SDG #13 since completion of the 100-hour run test on August 6, 1987 and, to date, no valid failures have occurred.

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NL.88.104.01