ST-HL-AE-2749, Special Rept:On 880707,diesel Generator Nonvalid Failure Occurred During Monthly Operability Surveillance of Standby Diesel Generator 12,resulting in Loss of Primary Starting Circuit.Caused by Dislodged Relay

Special Rept:On 880707,diesel Generator Nonvalid Failure Occurred During Monthly Operability Surveillance of Standby Diesel Generator 12,resulting in Loss of Primary Starting Circuit.Caused by Dislodged Relay

ML20207C937
Person / Time
Site:	South Texas
Issue date:	08/03/1988
From:	Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
ST-HL-AE-2749, NUDOCS 8808110005
Download: ML20207C937 (4)

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August 3, 1988 ST-HL-AE-2749 File No.: G02 10CFR50.36 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Unit 1 Docket No. STN 50-498 Special Report Regarding A Diesel Generator Nonvalid Failure on July 7, 1988 Pursuant to the South Texas Proj ect 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 July 7, 1988.

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

G. E. Vaughn Vice President Nuclear Plant Operations GEV/BEM/nl i

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Attachment:

Special Report Regarding a Diesel Generator Nonvalid Failure on July 7, 1988 l

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s A Subsidiary of Ilouston Industries incorporated

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CCI 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 George Dick U. S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Center 1100 Circle 75 Parkway Jack E. Bess Atlanta, Ga. 30339-3064 Resident Inspector / Operations c/o U. S. Nuclear Regulatory Commission Dr. Joseph M. Hendrie P. O. Box 910 50 Be11 port Lano -

Bay City, TX 77414 Be11 port, NY 11713 Don L. Garrison Resident Inspector / Construction 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 1

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Revised 06/16/88 NL.DIST

Ilouston 1.ighting & Power Company Attachment ST-HL-AE-2749 Page 1 of 2 South Texas Project Electric Generating Station -

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} Docket No. SIN 50-498 +

j Special Report Regarding A Diesel Generator Nonvalid Failure on July 7, 1988 l

DESCRIPTION OF EVENT:

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On July 7, 1988, the monthly operability surveillance of Standby Diesel Generator (SDG) #12 was being performed following completion of physical work to install a SDG remote emergency stop button in the Main Control Room. At 2229 hours0.0258 days <br />0.619 hours <br />0.00369 weeks <br />8.481345e-4 months <br />, SDG #12 was started in the emergency mode and subsequently released to the test mode for synchronization with offsite power and test loading. Operators were unable to synchronize the generator due to loss of engine governor speed control. The blue "READY TO LOAD" light on the Main Control Panel in the Control Room was observed to flicker and go out. The surveillance was suspended and the engine shut down at 2237 hours0.0259 days <br />0.621 hours <br />0.0037 weeks <br />8.511785e-4 months <br />.

A Maintenance Work Request was processed for Electrical Maintenance to investigate the problem. Relay 63QELX2 in the emergency low lube oil shutdown circuit was found pushed down about 30 degrees below horizontal. Although the

[ retaining clip was in place, some of the relay pins had lost electrical contact with the base socket. From the symptoms reported by operators, the relay coil pins apparently made some initial minimal contact but subsequently broke contact with the base socket.

The loss of relay 63QELX2 resulted in the loss of the primary starting circuit, either before the engine was started in emergency or shortly thereafter. The primary starting circuit is required to synchronize in the test mode. There is a redundant starting circuit which is nearly identical to i

I the primary starting circuit and is sufficient to start and permit emergency loading of the SDG if the primary circuit is disabled. The "READY TO LOAD" indication comes from the primary circuit but does not reflect the status of l

the redundant circuit. Therefore, loss of the "READY TO LOAD" indication did not* indicate a failure of the redundant starting circuit.

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NL.88.208.01

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lh>usom i.i>;hting & Power unnpany j Attachment ST-HL-AE-2749 Page 2 of 2 DESCRIPTION OF EVENT Cont.d Electrical Maintenance corrected the problem by pushing the 63QELX2 relay back into its socket. Proper function and indication were restored to the system, as demonstrated by successful performance of the operability surveillance on July 8, 1988.

This start is classified as a nonvalid failure in accordance with RG 1.108, sections C.2.e.(2) and C.2.e.(5) (1. e., a successful start followed by an unsuccessful loading attempt due to failure of synchronizing circuitry).

Although the primary starting circuit became inoperable, the SDG would have been able to start, accelerate and load in the emergency mode.

ROOT CAUSE Work was performed on the 63QELX2 relay and an adjacent relay, SER1, during installation of the SDG #12 remote emergency stop button. The probable root cause of failure is that relay 63QELX2 was dislodged during the installation of wiring to its base or during wiring of the adj acent relay.

CORRECTIVE ACTION:

Craft personnel performing modification work will receive additional training by September 6, 1988. This incident will be brought to their attention, with l

emphasis on the need to not only to be careful but to also be aware that their actions can affect equipment beyond the scope of the work they are doing.

l 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 test interval for SDG #12 remains 31 days. There have been twenty-three (23) valid tests performed on SDG #12 since the Unit I license became effective and, to date, no valid failures have occurred.

NL.88.208.01