ML20154M018

Special Rept 87-016-01:on 871219,diesel Generator B Failed When Generator Could Not Be Synchronized to Bus.Caused by Potential Transformer Fuse Knives Not Inserting Fully Into Fuse Stabs.Insp Windows on Each Cubicle Recommended

ML20154M018
Person / Time
Site:	Wolf Creek
Issue date:	05/27/1988
From:	Withers B WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
87-016-01, 87-16-1, WM-88-0138, WM-88-138, NUDOCS 8806010146
Download: ML20154M018 (4)

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W4)NUCi. LF CREEK EAR OPERA ING CO Bart D. Wsthers me.ani e Ch.ef Esecueve Othcor May 27,1988 WM 88-0138 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk t'ashington D. C. 20555

Subject:

Docket No. 50-482 : Special Report 87-016-01 Gentlemen:

The attached supplemental Special Report is being submitted pursuant to Technical Specifications 4.8.1.1.3 and 6.9.2. This report concerns a failure oi Emergency Diesel Generator "E" 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 staf f.

Very truly yours, Bart D. Withers President and Chief Executive Officer BDW/jad Attachment cc: B. L. Bartlett (NRC), w/a R. D. Martin ( NRC) , w/a P. W. O'Connor (NRC), w/a (2) 8806010146 G80527 PDR ADOCK 05000482 / 4j S DCD f, ff/ V

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P.O. Box 411 i Burhngton, KS 66839 / Phone- (316) 364 8831 An EcuW C45crwrwy Empoyer IA F HCVET

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Attachuent to WM 88-0138 Page ) . of 3 WOLF CREEK GENERATING STATION ,

SPECI AL REP 0tT 87-016-01 DIESELGENERATORlB' FAILURE INTRODUCTION On December 19, 1987, at approximately 1442 CST, a failure of Diesel Generator .(D/G) 'B' occurred when the D/G could not be synchronized to the bus.: The D/G was unavailable for approximately 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 being submitted pursuant to Technical Specifications 4.8.1.1.1 and 6.9.2.

ANALYSIS _OF EVENT The D/G was at speed and attempting to be synchronized during the yearly 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. run when the failure occurred. Maintenance was notified by Control Room personnel to investigate-the problem.- The cause of the failure was detemined- to be a result of the potential transformer fuse knives not inserting. fully into the fuse stabs, which caused an unstable voltage output. To cesolve the problem, the circuit closing linkage was adjusted to provide enough force to insert the knives. 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 recommenced at approximately 0126 CST on December 21.

The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> run and associated testing was completed successfully at approximately 0915 CST on December 22.

ROOT CAUSE AND CORRECTIVE ACTIONS The failure of the circuit closing linkage to insert the knives into the stabs properly was a result of the repeated opening and closing of the rotating potential transformer (PT) and the lack of a checking method. When the PT is rotated and lowered back into place a number of times, the adjustment on the linkage can be forced out of the proper closing position, thus prohibiting proper contact. At present, it is not possible to visually detect the subject problem since the circuit closing linkage inserts the knives into the stabs only after the PT compartment cubicle door is closed.

The first indication of this problem is when the PT does not function properly. Therefore, an engineering evaluation has been completed that recommends installation of inspection windows on the front of each cubicle.

This will provide a fuse insertion checking method after closing the cubicle doors. A conceptual outline of the proposed window design is provided in Figure 1.

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Attachment to WM 88-0138 Page 2 of 3 This proposed design is in the process of being finalized following the completion of an internal examination of the subject cubicle. From this examination it has been de t e rmined that the adjustment of the circuit closing linkage allows the knives to insert into the stabs. Furthermore, if the knives are not fully inserted with the addition of the inspection window to each cubicle, the problem can be detected and resolved by opening and closing the cubicle door one time. This examination was necessary to confirm internal compartment clearances. The subject linkage was also examined during this inspection and found acceptable provided the adjustment to the linkage is maintained.

ADDITIONAL INFORMATION The output of the failed PT provides control power to the static exciter / voltage regulator and to the Woodward Governor control box.

Tne function of the static exciter / voltage regulator is to control the electrical output of the diesel generator through direct static excitation of the generator field winding. The subject PT provides the control voltage required for automatic voltage regulation.

The function of the Woodward Governor control box is to electrically control the speed of the diesel generator by controlling the fuel to the engine.

The Woodward Governor also provides a mechanical governor system that will maintain speed control after a loss of control power to the electrical governor system.

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

voltage and to demonstrate that 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 not provide the control voltage required to maintain automatic voltage regulation, the D/G could not be synchronized to the bus and, thus could not be successfully loaded af ter a successful start attempt. This 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, Revision 1.

As of May 14, 1988, there have been f orty-six (46) valid successful tests of D/G 'B'. This is the first valid f ailure of D/G 'B' . This event was the first valid failure in the last 20 valid tests and therefore did not affect the testing frequency of once per 31 days as required by Technical Specification Table 4.8-1.

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