ST-HL-AE-4270, Special Rept:On 921022,nonvalid Failure of Standby DG 12 Occurred During Standby DG Operability Surveillance Test. Caused by Tripped Generator Breaker Lockout Relay at Local Control Panel.Surveillance Procedures to Be Revised

Special Rept:On 921022,nonvalid Failure of Standby DG 12 Occurred During Standby DG Operability Surveillance Test. Caused by Tripped Generator Breaker Lockout Relay at Local Control Panel.Surveillance Procedures to Be Revised

ML20117A502
Person / Time
Site:	South Texas
Issue date:	11/20/1992
From:	Jump W HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-4270, NUDOCS 9211300076
Download: ML20117A502 (5)

Text

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• llouston 1.ighting A l'ower November 20, 1992 ST-llL-AE-4270 File No.t G02 10CFR50 U. S. Nuclear Regulatory Commission Attention: Document Control Dock Washington, DC 20555 South Texas Project Unit 1 Docket No. STN 50-490 Special Report Regarding a Non-Valid Failure of Standby Ditqql Generator 12 on October 22, 1931 I'ursuant to the South Texas Project Electric Cenerating Station (STPEGS) Technical Specifications 4.8.1.1.3 and 6.9.2, llouston Lighting & Power submits the ettached Specja.' Report regarding a non-valid failure of Standby Diesol Generator 12 which occurred on October 22, 1992.

If you should have any quet,tions on this matter, please contact Mr. C. A. Ayala at (512) 972-8628 or me at (512) 972-7205.

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L William J. Jump F General Manager, Nuclear Licensing MAC/ag Attachment. Special Report Regarding a Non-Valid Failure of SDG 12 on October 22, 1992 b t! b O l$ a mnem.m / , n ^!~ I A snmuarv or liouston Indusnin incorporated 9211300076 921120

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4 lloudon Lightig & Power Company ST-HL-AE-4270 South Texa Project Elettric Generating Station File No.I G02 Pago 2 cc Regional Administrator, Region IV Rufus S. Scott Huclear Regulatory Commission Associato Gonoral Counsel 611 Ryan Plaza Drivo, Suito 400 Houston Lighting & Power Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 7720r Georgo Dick, Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Contor 1100 Circle 75 Parkway _

J. I. Tapia Atlanta, GA 30339-3064 Senior Resident Inspecto'c c/o U. S. Nuclear Regulatory Dr. Joseph H. Hendrio commission 50 Bellport Lano P. O. Box 910 Bellport, NY 11713 Bay City, TX 77414 D. K. Lacker J. R. Newman, Esquiro Bureau of Radiation Control Novman & Holtzinger, P.C. Texas Department of Health 1615 L Stroot, N.W. 1100 West 49th Street c Washington, DC 20036 Austin, TX 7P*/56-3189 D. E. Ward /T. H. Puckett Contral Power and Light Company P. O. Box 2121 Corpus Christi, TX 78403 J. C. Lanior/M. B. Lee City of Austin _

Electric Utility Department P.O. Box 1088 Austin, TX 78767 K. J. Fiedler/M. T. Hardt City Public Servico Boerd ,

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anknoio TX 78296 Revised 10/11/91 L4/NRC/

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Attachment ST-HL *4-4270 .

Page 1 of 3 South Texas Project Unit 1 Docket No. STN 50-498 Spscial Report Regarding a Non-Valla Failure of '

Standby Diesel Generator 12 on Octobei _12. 1992 P DESCRIPTION OF EVENT:

On October 22, 1992, Unit 1 was in no modo during a refueling outage. At 2102 hours0.0243 days <br />0.584 hours <br />0.00348 weeks <br />7.99811e-4 months <br />, Standby Diesel Generator (SDG) 12 was started in the emergency mode to perform the SDG operability surveillance test. The SDG was released from emergency to the test mode and an attempt was made to parallel the SDG witn the offsite power source. The SDG output breaker was cycled shut and reopened. Two additional attempts were made to clase the breaker with almilar results. The SDG was placed in cooldown and the test suspended. The Generator Breaker 7,ockout Relay (86GB) was found tripped at the local control panel.

The 86GB relay can be energized by any one of eight protective relays associated with individual generator fault conditions such as reverse power, loss of field, underfrequency, overcurrent and overvoltage. The presence of one of these conditions, which would lead to a trip of the 86GB relay, would be indicated by a flag on the associated protective relay, an alarm at the local panel, and a summary alarm on the Emergency Response Facility Data Acquisition Display System (ERFDADS) and in the Control Room. No flags were noted on the protective relays following this event and no alarms were received in the control Room or on ERFDADS. .

Troubleshooting was conducted on the circuits associated with relay 86GB and the related protective relays. Each protective relay was manually operated to verify that the 86GB relay tripped,.the rotective relay flag came in and the alarm was roccived in tr." Control Rtam: Each relay operated satisfactorily. Tne 86CB relay was tested to verify that the mechanical flag could not be cleared prior to opening the electrical contacts. There was no flag movement prior to the contacts opening. The control panels-were enecked for loose, burned or broken wiring. None were found. The generator breaker was cycled satisfactorily. The breaker closed as required during the post maintenance test. No physical problem could be identified to account for failure of the breaker to remain closed during the surveillance test.

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SREP\92-314.001 I_._.__...______...._.__.___.,_.-.___.,_._--,.___._...____, _ , - . , . _ _ _ _ . _ . . , . . , . _ _ _ _ _ _ . _ _ , . , - . _ _ . _ _ - , , . .

Attachment ST-HL-AE-4270 Page 2 of 3 l

DESCRIPTION OF EVENT: (Con't)

A 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run of SDG 12 had been successfully completed on October 22 at 0128 hours0.00148 days <br />0.0356 hours <br />2.116402e-4 weeks <br />4.8704e-5 months <br />. A review of work packages indicated

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that the Negative Phase Sequence overcurrent Relr.y (46) was i calibrated during the time between the tuo SDG runs. Relay 46 can actuate to trip the 86GB relay. Relay 46 is removed from the caso during the calibration process. The possibility exists that upon restoration of the relay following calibration, the relay inadvertently tripped, tripping the 86GB relay. The operator at the local control panel indicated he checked the panel for trip flags and none were observed privr to the test conducted at 2102 hours0.0243 days <br />0.584 hours <br />0.00348 weeks <br />7.99811e-4 months <br />. However, the operator did observe the trip flag during the subsequent attempts to close the output breaker. A standby lineup, which includes verifying lockout relays are reset, was not required to be performed prior to this test. This lineup is located in the SDG operating procedures. If thiu lineup had been requested, a problem with the 85GB relay could have been detected.

CAUSE OF EVENT:

The event was most likely caused by the 86GB relay being in the tripped condition prior to the start of the surveillance test. This may have occurred during calibration of the 46 relay.

This conclusion is based upon satisfactory operation of the protective relay circuits and the 86GB relay during troubleshooting. In addition, no protective relay flags or alarms were received during the event. The action of the breaker during this event (attempting to close then reopening) is consistent with the circuit design with a locked-in trip signal..

The protective relays, associated slave relays and relay 86GB energize to actuate, which minimizes the occurrence of spurious operation. The surveillance procedures on the SDGs do not require the performance of the standby lineup prior to operation.

ANALYSIS OF EVENT:

This event is classified as a non-valid failure since the SDG operated satisfactorily in the emargency mode, and if challenged, would have performec its safety function. The actuation of the 86GB relay to open the generator breaker is bypassed in the emergency mode.

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SREF\92-314.001 i

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Attachment ST-HL-AE-427C Page 3 of 3

_Q_QllRECTIVE ACTIONS:

1. Troubleshooting of the 86GB relay and related protective relay circuite was completed. No discrepancies vero noted with the system operation.

2. The appropriate surveillance procedures on the SDGs will be revised to require the performance of the SDG standby lineup prior to performing the surveillance. This action will be completed by April 27, 1993.

ADDITIONAL INFOEli&TTQH:

Por STPEGS Technical Specification 4.8.1.1, there has been 1 valid failure in the last 20 valid tests of SDG 12. The number of valid failures within the last 100 valid tests is less than or equal to 4. Therefore, the testing .requency for SDG 12 remains at once per 31 days.

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l SREP592-314 J01

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