View source for ST-HL-AE-3960, Special Rept:On 911212,standby Diesel Generator 11 Nonvalid Failure Occurred Due to High Resistance of Relay Contacts within Instantaneous Preposition Board.Instantaneos Preposition Board Replaced & Similar Relays to Be Inspected

{{Adams
| number = ML20087D344
| issue date = 01/10/1992
| title = Special Rept:On 911212,standby Diesel Generator 11 Nonvalid Failure Occurred Due to High Resistance of Relay Contacts within Instantaneous Preposition Board.Instantaneos Preposition Board Replaced & Similar Relays to Be Inspected
| author name = Jump W
| author affiliation = HOUSTON LIGHTING &amp; POWER CO.
| addressee name = 
| addressee affiliation = NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
| docket = 05000498
| license number = 
| contact person = 
| document report number = ST-HL-AE-3960, NUDOCS 9201160102
| document type = REPORTABLE OCCURRENCE REPORT (SEE ALSO AO LER), TEXT-SAFETY REPORT
| page count = 4
}}

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The Light c o mp a nySouth Texas Pmjw Elutric Genes atingP.Station                          O. Box 289 Wadsworth. Te s ai 77481 Iluuston Lighting & I,ower____ __ _ _ _ _ _ . - . _ _ . _             _ _ . _ _ _      _ _ . . . .    . _ _ _     _ .
January 10, 1992 ST-llL.AE 3960 File No.: C02 10CFR50 U. S. Nuclear Regulatory Commission                                                                                      l Attention: Document Control peak Washington, DC        20555 South Texas Project Electric Generating te.ation Unit 1 Docket No. STN 50 498 Special Report R'6arding a Standby Diesel Generator #11 Nonvalid Failure on December 12. 1991 Pursuant to the South Texas Pro p t Electric Generating Station (STPECS)
Technical Specifications 4.8.1.1.3 and 6.9.2, llou.aton Lighting & Power submits the attached Special Report regarding a Standby Diesel Generator (SDG) #11 norvalid failure which occurred on December 12, 1991.
If you should have any questions on this tnatter, please contact Mr. C. A. Ayala at (512) 972 8628 or me at ($12) 972 7205.
Y                                ,
n William J. Jump Manager, Nuclear Licensing CAA/1f

==Attachment:==
Special Report Regarding a SDG n11 Nonvalid Failure on December 12, 1991
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          ,9201160102 920110 4
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            .-        Ilouston Lighting & Power Cornpany             ;         File No.: CO2 South Texas Projed Electric Generating Station           Page     2 cci
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i Regional Administrator, Region IV                  Rufus S. Scott                   [
Nuclear Rey,ulatory Commission                     Associate Ci e al Counsel        !
611 Ryan Plaza-Drive, Suite 400                    Houston Ligh,.ag & Power Company e Arlington, TX 76011                                P. O. Box 61867                  !
Ilouston, TX 77208 George Dick, ' Project Manager
                   .U.S. Nuclear Regulatory Comraission                 INPO Washington, DC 20555                               Rect. rds Center 1100 circle 75 Parkway I'                                                               Atlanta, CA 30339 3064 J. 1. Tapia Senior Resident Inspector                                                           ,
c/o U. S. Nuclear Regulatory                       Dr. Joseph H. Hendrie Comnission                                       50 Be11 port Lane P. 0. Box 910                                      Be11 port, in 11713 Bay City, TX 77414 D. K.-Lacker J. R. Newman, Esquire                              Bureau of Radiation Control Newman 6 lloitzinger, P.C.                         Texas Department of llealth 1615 L Street, .N.W.                              .1100 West 49th Street
                   .Vashington, DC 20036                                Austin, TX 78756 3189 D. E. Ward /T. M. Puckett' Central Power and Light Company P. 0, Box 2121 Corpus Christi, TX 7'403 e                 'J. C. Lanier/M.       B,' Les City of Austin Electric Utility Depr.rtment P.O.. Box 1088 Austin, TX 78767 K. J. Fiedler/M..T. Hardt City Public Service Board-P. O. Box-1771-
_ San: Antonio, TX. 78296 Revised 10/11/91 L4/NRC/

I Attachment ST litr AE 3960 Pagn 1 of 2 South Texas Project Electric Generatin6 Station Uni; 1 Docket No. STN 50 498 Special Report Regarding a Diesel Cencrator #11 Nonvalid l' allure on Deccaber 12. 1991 DI1Ch}UlQR_ Ole EVEN1:
On December 12,1991 at 0203 hours, Unit I was in Mode 1 at 100t power.
During performance of procedure 1 PSP 03 DG 0001, Standby Diesel 11 Operability Test, with the engine at full load, 5600 kV, the generat'r output breaker tripped open due to instantaneous direction overcurrent, fr.or to the opening of the breaker, Standby Diesel Cenerator ;SDG) #11 was started in the emergency mode in accordance witt, the procedure and attajned rated speed, voltage, and frequency within the 10 second time limit. The SDG was released from the emergency mode and paralleled to the grid to load the engine. After SDG #11 was at full load, three attempts were made to raise reactive load above 3400 kVAR to obtain the most effic!cnt operating teactive load conditions which is be*=^en 3400 and 3600 kVAR. This van accomplished by lowering to 3100 kVAR -nd then raising to 3400 kVAR. The generator would not go above 3400 kVAR.                          On the second and third attempts to raise the reactive load, the voltage adjusting switch was released when reactive load would not go above 3400 kVAR. Approximately six minutes after the generator was et full load, the reactive load meter pegged h!.gh, the volt meter reading raised to approximately 5.0 kV (SDG design volta 6e is 4.16 kV) and the output breaker subsequently tripped open. The main control room indications were 4.9 kV, O kVAR, 61.2 liz, and 0 Amps. No switches were being manipulated at the time.
The design of the SDG voltage regulatar is such that when in the emergency mode, the instantaneous preposition board functions to bring the SDG up to the designed emergency bus voltage of approximacely 4.16 kV, without the need fot operator action. Once released from the emergency mode, telay contacts on this board change state and the current path bypasses the fixed resistance reference voltage circuitry and is routed directly from a motor operated potentiometer (MOP) to the voltage regulator.
It is suspected that the MOP was driven to the maximum limit when attempting to go above 3400 kVAR during tl.e third attempt and a contact problem in the preposition board affected the circuit resistance, thereby not initially allowing the increase in kVAR and voltage. With the preposition board adversely affecting the voltage regulating circuit, the MOP setting which normally would raise the SDG reactiva load, did not result in voltago regulator response until the preposition board changed state. After approximately six minutes of operation, current flow or energization of the preposition board contacts led to a decrease in contact sesistance (i.e., the problem cle ared itself) which subsequeatly changed the signal to the voltage regulator, causing the over voltage condition.
SEEPi91-361.001

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3 Attachment ST. lit.At.3960 Page 2 of 2 CAUSE OF EVENT:
The cause' of this event is attributed to high resistance of relay contacts within the inrtantaneous proposition board which affected control of kVAR and voltage in the para 1101 mode.
ANALYS15 0F EVENI:
W                   This incident is classified as a nonvalid failure since SDG #11 operated tsatisfactorily in the emergency mode and if challenged would have performed its safety function. The voltage regulation problems were experienced only after the SDG was released from emergency to test maje. This voltage regulation circuit is bypassed in the emergency mode.
CORRECTIVE ACTIONS:.
: 1.        The instantaneous-preposition board was replaced.
: 2.       .STPEGS will perform a detailed analysis of the preposition board and the SDG relay panel environment to determine the cause for high resistance of the relay contacts on the board. This analysis will be completed by March 26, 1992. Additional corrective actions will be developed as necessnty.
STPEGS will inspect similar relays on other SDGs at STPEGS for high contact resistance by June 12, 1992, h*E,AL INFORMATION:
                   , Per Technical Specification 3.8.1.1, there has been one valid failure in the last 20 valid = tests and one valid failure in the last 100 3alid~ tests on SDC #11; therefore, the testing. frequency will remain at once per 31 days.-
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