ST-HL-AE-3089, Special Rept:On 890406,standby Diesel Generator 12 Failed. Caused by Failed Resistor in Power Supply Circuit of Electronic Governor.Resistor Replaced & Generator Tested

Special Rept:On 890406,standby Diesel Generator 12 Failed. Caused by Failed Resistor in Power Supply Circuit of Electronic Governor.Resistor Replaced & Generator Tested

ML20246H890
Person / Time
Site:	South Texas
Issue date:	05/08/1989
From:	Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3089, NUDOCS 8905160217
Download: ML20246H890 (4)

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The Light i

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llouston Lighting & Power._.- -

May 8, 1989 ST-HL-AE-3089 File No.: G02 10CFR50.36(c)(5)

U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Unit 1 Docket No. STN 50-490 Special Report Recerding A Valid Failure of #12 Standby Diesel Generator on April 6, 1989 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 valid failure of the #12 Standby Diesel Generator on April 6, 1989.

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

GXAp -

G. E. Vaughn k .

Vice President Nuclear Plant Operations GEV/BEM/eg

Attachment:

Special Report Regarding A Valid Failure of #12 Standby Diesel Generator on April 6, 1989 l

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1 8905160217 PDR 890508 l I

S ADOCK 00000498 PDC NL.89.115.01 A Subsidiary of Ilouston Industries Incorporated I

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Houston Lighting & Power Company -

ST-HL-AE-3089 File No.: G02 10CFR50.36(c)(5) cc U. S. Nuclear Regulatory Commission Rufus S. Scott Attention: Document Control Desk Associate General Counsel Washington, D. C. 20555 Houston Lighting & Power Company P. O. Box 1700 Houston, TX 77001 George Dick, Project Manager U. S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Center 1100 Circle 75 Parkway Jack E. Bess Atlanta, Ga. 30339-3064 Senior Resident Inspector-Unit I c/o U. S. Nuclear Regulatory Commission Dr. Joseph M. Hendrie P. O. Box 910 50 Be11 port Lane Bay City, TX 77414 Be11 port, NY 11713 J. I. Tapia Senior Resident Inspector-Unit 2 c/o U. S. Nuclear Regulatory Commission P. O. Box 910 Bay City, TX 77414 J. R. Newman, Esquire Newman & 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 City Public Service Board P. O. Box 1771 San Antonio, TX 78296 j Revised 12/21/88 NL.DIST

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1 Thiuston Lighting & Power Company i

Attachment ST-HL-AE-3089 Page 1 of 2 l

South Texas Project Electric Generating Station q Unit 1 q Docket No. STN 50-498 )

Special Report Regarding A Valid I Failure of #12 Standby Diesel Generator on April 6, 1989 Description of Occurrence l On April 6, 1989, Unit I was in Mode 1 at 94% reactor power. At 0554 hours0.00641 days <br />0.154 hours <br />9.160053e-4 weeks <br />2.10797e-4 months <br /> Standby Diesel Generator (GDG) #12 was started in the emergency mode for surveillance testing. It came up to rated speed and voltage in less than ten seconds, then the speed began falling off and the frequency fell to 55 Hz.

The SDG was manually placed in emergency stop.

The SDG was started again at approximately 0800 hours0.00926 days <br />0.222 hours <br />0.00132 weeks <br />3.044e-4 months <br /> on April 6, 1989 in the test mode to determine if the problem was restricted to emergency mode circuit. The SDG was manually stopped after it displayed the same characteristics as it did in the emergency mode. The SDG was started again at approximately 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br /> on April 6, 1989 for further troubleshooting. This time the electronic governor was isolated and the mechanical governor was used for speed control. The SDG started normally and did not trip or display the abnormal conditions that were previously experienced. Troubleshooting was conducted or the electronic governor, and it was determined that a resistor in the power supply circuit had failed. The resistor was replaced and the SDG was successfully tested at 1855 hours0.0215 days <br />0.515 hours <br />0.00307 weeks <br />7.058275e-4 months <br /> on April 6, 1989.

Cause of Occurrence:

The cause of this valid failure was a failed resistor in the power supply circuit of the electronic governor.

Analysis of Event:

This event occurred as a result of the failed resistor which inhibited the electronic governor from performing per design. Per the criteria in Regulatory Guide 1.108, this event has been classified as a valid failure. In the event of an actual challenge of the SDG, it would not have operated properly.

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P Attachment-L ST-HL-AE-3089 Page 2 of 2' Corrective Action:

The'following corrective actions are being taken as a result of this svents-

1. The power supply resistor in Standby Diesel Generator #12 was replaced'on April 6, 1989.

2. An evaluation of the failed resistor will be performed by Engineering to

- determine the failure mode and identify any further corrective actions, if needed. This evaluation will be completed by June 15, 1989.

i Additional Information j l

Three similiar events occured at the Palo Verde Nuclear Generating Station.

The cause of those events was attributed to f ailure of a power supply: resistor due to elevated DC distribution system voltages. Based on a review of the special report submitted by Arizona Public Service (APS) on the events and l discussions with APS engineers, HLGP engineering has concluded that the  ;

elevated voltages described do not exist at the South Texas Project.

Therefore, based on information collected to date, it has been determined that j the Palo Verde failures do not indicate a cause for immediate corrective  !

-action at STP until further evaluation is completed.

Per the criteria of Regulatory Guide 1.108, the failure described'in this l report has been classified as a valid failure. This is the first valid failure in 33 valid tests. As such, the test interval remains at 31 days.

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