ML20148A408

Special Rept 87-016:on 871219,failure of Emergency Diesel Generator B Occurred When Generator Not Synchronized W/Bus. Caused by Repeated Opening & Closing of roll-out Potential Transformer.Engineering Evaluation in Progress

ML20148A408
Person / Time
Site:	Wolf Creek
Issue date:	01/14/1988
From:	Withers B WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
87-016, 87-16, WM-88-0015, WM-88-15, NUDOCS 8801220530
Download: ML20148A408 (3)

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4 e W4) LF NUCLEAR CREEKOPERATING Bart D. Withers gg M January 14, 1988-VM 88-0015 U. S. Nuclear Regulatery Commission ATTN: Document Control Desk Washington D. C. 20555

Subject:

Docket No. 50-482: Special Report 87-016 Gentle 11en:

The attached Special Report is being submitted pursuant to Technical Specifications 4.8.1.1.3 and 6.9.2. This report concerns a failure of Emergency Diesel Generator "B" which occurred when the diesel generator could not be synchronized to the bus.

If you have any questions concerning this matter, please contact me or Mr. O. L.

Maynard of my staff.

Very truly yours,

, . 2 1 Bart D. Withers President and Chief Executive Officer BDW/llk Attachment oc B. L. Bartlett (NRC), w/a R. D. Martin (NRC), w/a P. V. O'Connor (NRC), 2 w/a I

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S PO. Box 411/ Burvngton, KS 66839 / Phone: (316) 364-8831 I 82 S DCD

Attachment to WM 88-0015

. Page 1 of 2 January 14, 1988 WOIE CREEK GE2iEHATING STATION TFEIAL REPORT 87-016 DIESEL GENEPA'IOR 'B' FAIIlJRE INTRODUCTICH On Decerrber 19, 1987, at approxim tely 1442 CST, a failure of Diesel Generator (D/G) 'B' occurred when the D/G oJuld not be synchronized to the bus. The D/G was unavailable for approximtely 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> and 44 minutes while the problem was corrected. This Special Report is beirr3 subnitted pursuant Technical Specifications 4.8.1.1.3 and 6.9.2.

ANALYSIS OF EVENT

'Ihe D/G was at speed and attempting to be synchronized during the yearly 24 Mur run when the aranaly occurred. Maintenano3 was notified by Control Pocm perscnnel to investigate the problem. The cause was determined to be a bent stab on the potential transformer. The stab was adjusted back into place. The D/G was returned to service and the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run reccumenced at approximately 0126 CST cn December 21. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run arri associated testing was completed successfully at apprcximately 0915 CST on De e r 22.

IOOT CAUSE AND CORRECTIVE ACTIONS

'Ihe bent stab was caused by repeat.ed opening arx3 closing of the roll-out potential transformer (PT). As the PT is rolled back into place arxl if the stab does not realign properly, the stab could be bent and thus rot allowing proper contact. It is not possible to visually detect this problem, as it is not visible with the PT closed. The first indication that this problem exists is when the PT does not function properly. An engineering evaluation is in progress to either preclude the stabs frcm being bent or u alloa a visual examination of the stabs after the PT is closed. A supplement to this report will be issued upon conpletion of this evaluation.

ADDITICNAL INwk4ATICN he output of the failed PT provides contIV1 poaer to the static exciter / voltage regulator an1 to the Wocx} ward Governor control box.

We function of the static exciter / voltage regulator is to cantrol the electrical output of the diesel generator thrux3h direct static excitaticn of the generator field wirx11ng. We subject PT provides the control voltage requira3 for autcmatic voltage regulation.

We function of the Woodward Governor control box is to electrically control the speed of the diesel generator. The Wcolaard Governor also provides a mrhanical governor system that will maintain speed control after a loss of cantrol power to the electrical governor system.

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Attachment to WM 88-0015

. Page 2 of 2 January 14, 1988 J

Regulatory Guide 1.108 requires that diesel generator testing be performed to "denonstrate proper startup operation by simulating loss of all a.c.

voltage and to denonstrate that the diesel generator can start automatically and attain the required voltage and frequency within acceptable limits and time" at least once every 18 months. Because the subject potential :

transformer could rot provide the control witage required to maintain

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autcmatic voltage regulation, the D/G could not be synchronized to the bus and, thus could not be successfully loaded after a successful start attempt. 'Ihis event is therefore considered to be a valid test and failure in accordance with Regulatory Position C.2.e.(5) of Regulatory Guide 1.108, Revisicn 1.

As of January 5,1988, there have been forty-one (41) valid successful tests of D/G 'B'. This is the first valid failure in the last 20 valid tests and therefore does not affect the current testing frequency of once per 31 days as required by Technical Specification Table 4.0-1.

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