ML20006B222

LER 89-023-00:on 891216,standby Diesel Generator 11 Failed Tech Spec Required Operability Test & Attempt to Secure Essential Chiller 12C Resulted in Trip.Caused by Failure of Voltage Regulator.Regulator Returned to mfg.W/900116 Ltr

ML20006B222
Person / Time
Site:	South Texas
Issue date:	01/16/1990
From:	Ayala C, Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-023-01, LER-89-23-1, ST-HL-AE-100001, NUDOCS 9002010115
Download: ML20006B222 (6)

Text

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'The Light-P.O. Box 1700 Houston, Texas 77001 (713) 228 9211 Houston Lighting 8e Power _--

January 16, 1990 j ST-HL- AE-10 0001 File No.: G26 10CFR50.73  !

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U. S. Nuclear Regulatory Commission Document Control Desk Attention: '!

Washington, DC 20555 South Texas Project Electric Generating Station Unit 1 Docket No. STN 50-498 Licensee Event Report 89-023 Regarding A Technical Specification Required Shutdown due to a Diesel Generator Valid Failure and an Essential Chiller Failure Pursuant to 10CFR50.73, Houston Lighting & Power Company (HI.&P) submits the attached Licensee Event Report (LER 89-023) regarding a Technical Specification required shutdown due to a diesel generator valid failure and an essential chiller failure. This event did not have any adverse: impact on the health and safety of the public.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972-8628 or myself at (512) 972-7921.

G.E.bpn G._E. Vaughn Vice President I Nuclear Operations GEV/BEM/n1

Attachment:

LER 89-023 (South Texas, Unit 1) 9002010115 900116 +

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ST-HL.AE- 100001 Hduston Lighting & Power Company South Texas Project Electric Generating Station File No. : G 26 Page 2 of 2 cc:

Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Hnuston Lighting & Power Company Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INFO Washington, DC 20555 Records Center 1100 Circle 75 Parkway J. I. Tapia Atlanta, GA 30339 3064 Senior Resident Inspector c/o U. S. Nuclear Regulatory Dr. Joseph M. Hendrie Commission 50 Be11 port Lane P. O. Box 910 Be11 port, NY 11713 Bay City, TX 77414 D. K. Lacker J. R. Newman, Esquire Bureau of Radiation Control Newman & Holtzinger, P.C. Texas Department of Health 1615 L Street, N.W. 1100 West 49th Street Washington, DC 20036 Austin, TX 78704 D. E. Ward /R. P. Verret Central Power & Light Company P. O. Box 2121 Corpus Christi, TX 78403 J. C. Lanier Director of Ceneration 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 Revised 12/15/89 L4/NRC/

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On December 16, 1989, Unit I was in Mode 1 at 100 percent power. At 0242 hours0.0028 days <br />0.0672 hours <br />4.001323e-4 weeks <br />9.2081e-5 months <br />, Standby Diesel Generator (SDG) 11 failed its Technical Specification required operability test and was subsequently declared inoperable. At 2153 hours0.0249 days <br />0.598 hours <br />0.00356 weeks <br />8.192165e-4 months <br />, an attempt to secure Essential Chiller 12C was unsuccessful. The chiller was subsequently tripped locally and declared inoperable. A.

Notification of Unusual Event (NOUE) was declared and Technical Specification required shutdown was initiated due to the failure to satisfy Action d of Technical Specification 3.8.1.1. The chiller was restored to operability at l 1950 hours0.0226 days <br />0.542 hours <br />0.00322 weeks <br />7.41975e-4 months <br /> on December 17, 1989 and the shutdown and NOUE were terminated.

l The cause of the failure of SDG 11 was failure of the voltage regulator and associated relays. The voltage regulator has been replaced. The failed relaya have been replaced or repaired. The cause of the chiller failure was contact oxidation and low contact pressure on an auxiliary relay. The chiller auxiliary relay has been cleaned and adjusted."- Other similar relays will be inspected for this condition.

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On December 16, 1989, Unit I was in Mode 1 at 100 percent power. At 0232 hours0.00269 days <br />0.0644 hours <br />3.835979e-4 weeks <br />8.8276e-5 months <br />, Standby Diesel Generator (SDG) 11 was started to perform the monthly Technical Specification required surveillance test. The SDG started in-the emergency mode and attained rated voltage and frequency within ten seconds as  ;

required. The SDG was released from the emergency mode and paralleled to i offsite power for performance of the loaded portion of the test; however, it  ;

failed to pick up reactive load and subsequently failed to maintain output voltage when the generator output eaker was tripped. SDG 11 was secured and declared inoperable. Action b of T67hnical Specification 3.8.1.1 was then entered and troubleshooting of the vo:tage regulator was initiated.

As a result of Essential Cooling Water Pond low temperatures, each of the safety-related Essential Chillers was required to be started to verify that they were operable. At approximately 2053 hours0.0238 days <br />0.57 hours <br />0.00339 weeks <br />7.811665e-4 months <br /> on December 16, 1989, ,

Essential Chiller 12C was started. At 2143 hours0.0248 days <br />0.595 hours <br />0.00354 weeks <br />8.154115e-4 months <br /> an attempt to secure it from the main control panel was unsuccessful. The chiller was tripped locally at 2153 hours0.0249 days <br />0.598 hours <br />0.00356 weeks <br />8.192165e-4 months <br />. Technical Specification 3.8.1.1 Action d.1 requires that all required systems which depend on the remaining operable diesel generators as a source of power be verified to be operable. Since Essential Chiller 12C is associated with SDG 12, a Notification of Unusual Event (NOUE) was declared and a shutdown required by Technical Specification 3.8.1.1 Action d was

! initiated at 2355 hours0.0273 days <br />0.654 hours <br />0.00389 weeks <br />8.960775e-4 months <br />.

Troubleshooting of Essential Chiller 12C' identified contact oxidation and 1 light contact pressure on the 69X relay in the chiller control' circuit. This r

[ relay sends a trip signal to the 4160 Volt supply breaker to the chiller.

Failure to trip the chiller under loss of offsite power conditions would have prevented the output breaker of SDG 12 f rom closing and supplying power to the Train B safety-related bus. The relay contacts were cleaned and _ adjusted.  !

The chiller was returned to service at 1950 hours0.0226 days <br />0.542 hours <br />0.00322 weeks <br />7.41975e-4 months <br /> on December 17, 1989 and the NOUE was terminated at 2032 hours0.0235 days <br />0.564 hours <br />0.00336 weeks <br />7.73176e-4 months <br />, a

l Based on initial troubleshooting of SDG 11, components on the voltage regulator chassis were replaced and the diesel was restarted. The diesel was i immediately secured due to high output voltage. The entire voltage regulator

• chassis was replaced and a troubleshooting test run was completed i satisfactorily. However, during a subsequent troubleshooting test run, the generator failed to develop output voltage. Further troubleshooting '

identified that relays K1, K3 and K4 had failed in the voltage regulator circuit. Based on the sequence of events observed during testing, it is believed that the K1 relay, which prevents reinitiation of field flashing when i

the SDG is running unloaded, misoperated causing the fluctuating output voltages. Failure of the K3 and K4 relays has been preliminarily attributed-to an overcurrent condition which occurred when the voltage regulator failed.

The K1 relay-contacts were cleaned and burnished and the K3 and K4 relays were replaced. A successful surveillance test of SDG 11 was performed at 0454 hours0.00525 days <br />0.126 hours <br />7.506614e-4 weeks <br />1.72747e-4 months <br /> on Decomber 19, 1989.

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L CAUSE OF EVENT:

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The causes of the failur'e of SDG 11'were asLfollows:-

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1. Failure of the voltage regulator. The cause of-this failure is not known at this time. 3 r

2. Misoperation of the K1 relay due to contact pitting'. ,

i The cause of tha failuie of Essential Chiller 12C to trip on demand was.  !

contact oxidation and light contact pressure on the 69X relay in the supply.. q['

breaker control circuit.

The diesel generator K1 relays are testediroutinely as part of eac'.t DG'  !

surveillance test. The 69X relays in the essential chiller contr:1 circuits

- are tested each time a chiller is stopped. Therefore, a pragram is in. place  !

to detect degradation of these relays. These are the only instances identified to date where these relays have failed. At this. time, HL&P has not detected'a gen 6ric failure mechanism causing the failure of auxiliary relays. ,

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ANALYSIS OF EVENT:

Completion of a shutdown required by Technical Specifications is reportable pursuant to 10CFR50.73(a)(2)(1)(A). The plant was brought to an orderly shutdown with no unexpected transients. ,

l I CORRECTIVE ..T.ON:

, The following corrective actions have been identified as a result of.this events

1. The voltage regulator will be returned to the manufacturer for repair and identification of failed components. This data will-be reviewed  ;

to determine if any further corrective action is warranted.  ;

2. The K1 relays on the remaining diesel generators on both units will I have their contacts cleaned and burnished during the next scheduled train outages. These outages are currently scheduled for completion .

by July 21, 1990. i

3. The 69X relays in'the remaining 4160 Volt chiller control circuits will be inspected during the next scheduled train outages. These i~

outages are currently scheduled for completion by July 21,'1990, a

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l- ADDITIONAL INFORMATION: i

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-The voltage regulator is part no. 72-05000-100 manufactured by~Portec Electric- l

. Products, i Per the criteria'of_ Regulatory Guide 1.108,-the failure described in'this. I report has been classified as a.v.alid failure. This:is the first~ valid failure since completion of_the diesel generator reliability demonstration.

As such, the test interval for this SDG remains at once per 31 days. There '

have been a total of 53 valid tests of SDG 11 to date.'

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l The 69X' relay is a type AR Ultra High' Speed, Time'. Delay Release, High' Threshold model manufactured by Westinghouse. --;

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