U-602057, Special Rept:On 920921,generator Output Breaker Failed to Close on Four Attempts.Caused by Bent Protective Cover Over Auxiliary Switches & anti-pump Coil.Output Breaker Racked to Test Position & Sucessfully Cycled Three Times

Special Rept:On 920921,generator Output Breaker Failed to Close on Four Attempts.Caused by Bent Protective Cover Over Auxiliary Switches & anti-pump Coil.Output Breaker Racked to Test Position & Sucessfully Cycled Three Times

ML20115H686
Person / Time
Site:	Clinton
Issue date:	10/20/1992
From:	Spangenberg F ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
U-602057, NUDOCS 9210270287
Download: ML20115H686 (4)

Text

4 lLnois Pow;f Comp:ny ,

Chnton Power Statran P.O. Don 678 Chnton. IL 61727 1el 217 935-8881 o

U 602057 gg,g,gggpi>I5i u7 92(10-20)-tP POWER 8E.110e 10CFR50.36 October 20, 1992 >

Docket No. 50-461 Document Control Desk Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

"pecial Report: Valid Test Failure of Division I diesel Generator at Clinton Power Station (CPS)

Desr Sir: ,

Clinton Power Station (CPS) Technical Specification 4.8.1.1.3 1

requires all diesel generator failures, valid or non va .id, to be reported to the NRC within 30 days pursuant to Specification 6.9.2, SPECIAL REPORTS. Due to a valid failure of the Division I Diesel Generator (DCIA) during surveillance testing on September 21, 1992, the attached Special Report is being submitted in accordance with the CPS Technical Specifications to provide the information required by Regulatory Guide 1.108, Revision 1, " Periodic Testing of Diesel Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants," Regulatory Position C.3.b. In addition, this Special Report provides an update on the corrective actions 1taken or being taken in responwe to two previous valid failures of DG1A which were reported in-IP's Special Report dated August 19, 1992 (reference U-602035).

Submittel of this letter and its attachment satisfies.the requirements of CPS Technical Specifications 4.8.1.1.3 and 6.9.2 for submitting a Special Report for diesel generator failures.

-Sincerely;yours,

- e-r F. A. Spangenberg, III.

Manager, Licensing and Safety CLJ/msh cc: NRC Clinton Licensing Project Manager NRC Resident Office, V-690 Regional Administrator, Region III, USNRC Illinois Department of Nuclear Safety 921027068 9 b b0 l ADOCK 05000461 PDR S PDR -

V. / c7' h-:

4

1 Attachment to U 602057 Page 1 of 3 s

Description of Eveni At 0430 hours0.00498 days <br />0.119 hours <br />7.109788e-4 weeks <br />1.63615e-4 months <br /> on September 21, 1992, the Division I Dieswi Generator (DGIA) was started for routine surveillance per Clinton Poeer Station (CPS) Proceduro-9080.01, " Diesel Generator 1A (18) Operability Manual." Although DG1A rasched the required voltage nr.d frequency within the time specified by_

,,nical Specification 4.8.1.1.2, when the operator attempted to synchronize the generator to offsite power, the generat v output breaker failed to close.

The breaker also failed to close on the next four attempts. The breaker door l was opened, the closing spring was verified to be charged and the fuses were i vorified to be properly seated. No flags or other abnormalities were noted.  !

The door was reclosed, and the breaker successfully closed on the next attempt. -DG1A was then fully loaded and the surveillance test was completed without further problems.

Maintenance Work Request (MVR) D25008 was initiated to troab'4eshoot and l identify the cause of the breaker failure. Westinghouse _representativoo were brou6h t on-site to assist in troubleshooting. Upon investigation of the cubicle circuitry / components, minor problems were detected-with the phase to-phase undervoltage relays, but none would have prevented the breaker from closing. The associated main controi ^toom switches, control circuitry, ,

breaker cubicle truck operated contact (TOC) switch,' closing coil and spring ,

release coil were all found to operate satisfactorily, llowever, inconsistent '

resistance values were noted while monitoring the anti-pump relay coil during ,

troubleshooting. In addition, Maintenance personnel noted that the breaker

• closure circuitry fuse clip _ did not have the same amount of spread on the-clips as the fuse clip located in a spare cubicle. Although'this could have-been a contributing factor in the breaker failure. IP does not believe this to ce the root cause of the failure since a bad fuse clip connection would have resulted in a " service not available" indication alarm, which was not observed

- during the attempts to close the breaker. Regardless, the spare fuse clip was used to replace the original.

• While reassembling the original breaker, Maintenance personnel discovered that the protective cover over the auxiliary switches and the anti pump coil was bent in the area of the anti pump relay. It was noted that the cover was =

coming into contact with the relay plunger. IP concluded that this could have caused interference and prevented the relay from fully resetting-on an-

intermittent basis. . This problem would not have appeared during *he-attempts to recreate the failure since this cover was removed to provide < access to the -

test points that were monitored.

-Following replacement with a spare breaker, the output breaker was racked t.o the " test" position and successfully cycled three times. 1Rui replacement breaker was then racked into the." operate" position. At_2133 houra_on. -

September-23, 1992, DG1A was started. . The diesel generator was successfully  ?

synchronized with offsite power, loaded, end then unloaded three_ separate- -

times. No problems were experienced during _ breaker closure.. Based on the

~

completion of the operability surveillance and post-maintenance. testing of the installed spare breaker, DGIA was restored to operabic status at 0020 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />.on September 24, 1992.

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l Attachment to U 602057

• Page 2 of 3 l .

l l Eoot Cause/ Corrective Acth D5 As identified in IP's August .9 1992 Special Report, the output breaker for DG1A had previously failed to close during testing on July 17, 1992 and August 7, 1992. Failure of the til TOC switch was reported as the root cause of those output breaker failures. The ill TOC switch in the Division I output breaker cubille was replaced on August 7, 1992. In addition, the switches which perform a similar function in the Division 111 output breaker cubicle were subsequently inspected, and no abnormalities were noted. IP's August 19, 1992 Special Report stated that the TOC switches in the Division 11 output breaker cubicle were to be inspected / replaced by October 1, 1992, llowever, as a result of plant conditions which precluded removing the Division II Diesel Cencrator f rom service as planned, these switches were replaced on October 19, 1992, and no abnormal wear was identified. Deferral of this action was discussed with the NRC Resident inspector for CPS. Further, IP plans to -

inspect a representative sample of TOC switches in similar breaker cubicles in safety-related applications by the end of the fourth refueling outage (which is currently scheduled to begin in September 1993). The results of these inspections will be evaluated for further corrective actions.

The root cause of the most recent failure of the DGIA output breaker on September 21, 1992 has been determined to be the bent protective cover over the an.1-pump relay. The bent cover partially depressed the anti-pump relay plunger so that the contacts operated by '.he plunger were lightly touching.

This resulted in erratic operation of the relay. Also, the bent cover may have cocked the plunger to the side, thus interfering with its operation.

It was determined that there were two possible caures for the bent cover.

Either the cover was used as a foot rest as an aid for racking the breaker in or the cover hit a nearby concrete curb while the breaker was being racked out. Because the partially depressed plunger held the contacts in close proximity, any jarring of the breaker could cause the relay contacts to change state. Depending on the state of the relay contacts, the breaker could randomly Ieil to close. 1 Although the bent protective cover could have been a contributing factor to -

the previous failures, the original til TOC switches were shown to lose electrical continuity. Therefore, IP's determination that TOC switch failure was the root cause (or at least a contritating factor) for the previous feilures remains unchanged, and replacement of these switches was prudent or necessary. The contribution of the bent protective cover to the July 17, 1992 and August 7, 1992 failures is indeterminate.

As a result of the most recent failure, a corrective action plan was implemented. All of the other Class IE 4160. Volt Westinghouse breakers were inspected for damage to the protective cover, and no similar conditions were found. Operators and electricians were informed of the cause of the closure failure and a caution was issued on the INPO Operating Experience NETWORK about the interference with the anti-pump relay due to the bent protective cover. IP is returning the damaged breaker to Westinghouse to evaluate the condition of the breaker and identify any defects. The results of this evaluation are expected to be provided to IP by November 15, 1992. In addition, IP will have an independent root cause analysis organization, Failure Prevention, Inc., perform a fai..re analysis on the anti-pump relay

U-602057 Page 3 of 3 and TOC switch. *rhis is expected to be completed by Febt uary 1,1993.

Further, IP will monitor the closing circuit of the installed output breaker

- during several surveillar.cc tests of DCIA. The information gathered from both internal and external investigations will be evaluated sind any additional corrective actions will bo identified by February 28, 199,.

Test Interva)_e, As of September 21, 1992, DCIA had experienced six valid failures in the last 100 valid torts performed, and three valid failures fti the last 20 valid tests performed. In accordance with CPS Technical Spec.ifit.ation Table 4.8.1.1.2-1, DG1A continues to be tested at least once per seven days. This testing i

frequency will be maintained until seven consecutivo failure free demands have

} been perforrned and tha number of failures in the last 20 valid tests haa been

)_ reduced to one or less. ~

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