ML19354D740

Special Rept:On 891121,generator Voltage Regulator Transformer in Standby Diesel Generator 22 Local Control Panel Overheated.Caused by Missing Insulation Between Transformer Core & Mounting Bolt.Transformer to Be Replaced

ML19354D740
Person / Time
Site:	South Texas
Issue date:	12/21/1989
From:	Vaughn G HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3325, NUDOCS 9001020122
Download: ML19354D740 (4)

Text

. _ _ .

i The Li ht P.O. !!ox 1700 llouston, Tixas 77001 (713) 228 9211 .

Houston Lighting & Power . 1 I

December 21 1989 ST.HL AE. 33h5 File No.: C02  ;

100FR$0 ,

i U. S. Nuclear Regulatory Commission

!- Attention: Document Control Desk Washington, DC 20555 South Texas Project Electric Generating Station Unit 2 Docket No. STN 50 499 Special Report Regarding A Diesel Generator Valid Failure on November 21. 1989 Pursuant to the South Texas Project Electric Generating Station Technical Specifications 4.8.1,1.3 and 6.9.2, llouston Lighting & Power submits the attached Special Report regarding a diesel generator valid failure which occurred on November 21, 1989.

If you should have any questions on this matter, please contact Mr. C. A. Ayala at (512) 972-8628 or myself at (512) 9 2-7921.

G. E. Va Vice President Nuclear Operations '

GEV/BEM/nl

Attachment:

Special Report Regarding a Diesel Generator Valid Failure on November 21, 1989 '

9001020122 89122g

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ST HL.AE 3323 Ho.uston Lighting & Power Company

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ec:

Regional Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Compa ny Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 George Dick, Project Manager U.S. Nuclear Regulatory Commission INPO Washington, DC 20555 Records Center 1100 circle 75 Parkway J. I. Tapia Atlanta, CA 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. 14cker 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 I

Director of Generecion City of Austin Electric Utility 721 Barton Springs Road Austin, TX 78704 j R. J. Costello/M. T. Hardt l City Public Service Board l P. O. Box 1771 l San Antonio, TX 78296 1

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Revised 12/15/89 LA/NRC/

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Attachment ST-HL-AE- a25 Page 1 of 2 South Texas Project Electric Generating Station Unit 2 Docket No. STN 50-499 Special Report Regarding A DJesel Generator Valid Failure On November 21. 1989 Description of Event: 4 On November 21, 1989 Unit 2 was in Mode 5. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> load test on 1,,:

Standby Dicsel Generator (SDG) 22 was being performed to satisfy Technical }gg Specifications. Approximately 41.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> into the test, a plant operatot observed the generator voltage legulator transformer in the SDG local control .=

I panel to be overheating. At approximately 0230 hours0.00266 days <br />0.0639 hours <br />3.80291e-4 weeks <br />8.7515e-5 months <br />, thn test wt secured out of concern that the overheating observed could be a precursor to a fire.

Troubler' ooting was performed to determine the cause of the overheating.

It was noted that the overheating occurred at a mounting bolt which passes through phase B of the 4200/300 volt, 30 kVA voltage regulator transformer.

Due to its location, the bolt is required to be insulated to prevent induced currents from flowing through it to ground and causing excessive heating.

Visual inspection noted that the insulating material appeared to be missing from one end of the bolt. Electrical testing of the transformer indicated degraded performance of phase B.

Cause of Event:

The cause of the transformer overheating was missing insulation between

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the transformer core and mounting bolt. It is not known if this material was omitted by the vendor or omitted during installation at the plant site. No maintenance activities have been identified which would have resulted in removal of the insulation.

Corrective Action:

2 The following corrective actions are being takca as a result of this event:

l. The voltage regulator transformers on the other SDG's in both units ware visually inspected for evidence of overheating and for the presence of insulating washers. All appeared normal.

2. The voltage regulator transformer on SDC 22 will be replaced prior to completion of the corrective maintenance uork required as a result of a subsequent valid failure on November 28, 1989. This is E

currently ,.-heduled for completion by January 1, 1990.

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- Attachmsnt j ST-HL AE- 3325 t

Page 2 of 2

- Additional Information:

Per the criteria of Regulatory Guide 1.108, the failure described in

' this report has been classified as a valid frilure. This is the second valid failure in the last twenty valid tests; therefore, the test interval is changed to once per seven days from once per thirty-one days. There have been a total of twenty valid tests of SDG 22 prior to this failure since completion er of the diesel generator reliability demonstration.

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