ML20059E739

Special Rept:On 931206,one Valid & Two Invalid Failures of DG 1A Occurred.Caused by Failure of Exciter Field to Flash. Shutdown Relay K1 Replaced

ML20059E739
Person / Time
Site:	Catawba
Issue date:	01/04/1994
From:	Rehn D DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9401120213
Download: ML20059E739 (3)

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Dat e 1%,cr Com;aty D L Run (icitatebr h leur Ge::emhnn Depirtinent t'ge jVesident 4%!Akmord Rmd (803)%313?05 O!hte M. 5C 9741 (M)3)R113426 Fax DUKE POWER-January 4, 1994 i U. S. Nuclear Regulatory Commission ATTN: Document Control Desk i Washington, DC 20555 1

Subject:

Catawba Nuclear Station, Unit 1 ,

Docket No. 50-413 Special Report One Valid Failure and Two Invalid Failures of Diesel Generator 1A Pursuant to Technical Specification 4.8.1.1.3 and 6.9.2, find attached a Special Report concerning the Unit 1 Diesel Generator (DG 1A) one valid failure and two invalid failurus which occurred on December 6, 1993.

-I Very truly yours, l

DL Rehn i i

KEN \DGIA1206.93 Attachment xc: SD Ebneter Regional Administrator, Region II RJ Freudenberger Senior Resident Inspector RE Martin, ONRR

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SPECIAL REPORT CATAWBA NUCLEAR STATION DOCKET NO. 50-413 DIESEL GENERATOR 1A VALID FAILURE DUM TO FAILURE OF SIIUTDOWN RELAY IN FIELD FLASil CIRCUIT PIP l-C93-1069 A valid failure of Diesel Generator 1A (DG 1A) occurred on December 6, 1993 due to the failure of the exciter field to flash. Unit 1 was in Mode 6 (Refueling) for the lEOC7 refueling outage at the time of this failure.

This is the first valid failure in the last 20 valid tests and the first valid failure in the last 100 valid tests. Subsequently, following this valid failure, there were 2 invalid failures. DG 1A remains on a monthly operability test schedule in accordance with Technical Specification (TS)

4. 8.1.1. 2 Table 4. 8- 1. There is no unavailability time associated with this failure.

On December 5, 1993, DG 1A was manually started at 1352 (Start #988) for break-in runs following outage related maintenance. Throughout the break-in runn, no problems were encountered. At 2345, break-in runs were completed and System Engineering (SES) was contacted to begin performance testing of DG 1A.

At 0503 on December 6, 1993, Operations (OPS) started DG 1A (Start #992) per procedure OP/1/A/6350/02 (Diesel Generator Operation). It was immediately notice that the DG 1A output voltage did not rise, so the engine was manually shutdown down. This was start was classified as a valid failure.

SES initiated work order #93087775-01 for Instrument and Electrical (I AE) to investigate and repair the reason for the voltage not being established on DG 1A. lAE and Component Engineering (CES) began troubleshooting the problem under this work order. OPS started DG 1A at 0905 (Start #993) for the purpose of allowing lAE and CES to observe the available indications to help in determining the problem. It was cbserved that the exciter fteld voltage was not established indicating the field was not flashed.

A visual inspection of the components of the field flash circuit did not reveal any obvious abnormal conditions. Several key relay contacts were then connected to test equipment and then DG 1A was started at 1439 (Start

1. 994) with these points being monitored. It was discovered that _ the shutdown relay K1 was not resetting as designed when DG 1A was started. A new relay was retrieved from stock and the reset coil wac replaced.

The DG 1A engine was restarted at 1608 (Start #995) and the voltage output increased to 4160 volts. No other problems were observed. SES and OPS completed perf ormance testing on December 7, 1993, at and DG 1A was declared operable.

The field flash c ircu s.t provides the initial excitation to the generator field via the DG batteries. Once this field is established, the generator becomes self-excited and the voltage regulator provides the proper field voltage to maintain output voltage. The field flash circuit is comprised of three essential relay: the latch / reset (L/R) relay, shutdown (K1) relay, and field flash (FF) relay. These relays are interlocked to initiate and terminate the exciter field. Typically, on an engine start, the reset coil on the K1 relay should energize and mechanically disengage the contactor for K1 to allow the field to flash. This was not occurring during DG 1A Start

1. 994. The reset coil was not operating to release the mechanical latch.

Only the reset coil of the contactor assembly was replaced during this incident. The latch coil appeared to be in good working condition. There have been no other incidents of this relay failing at Catawba Nucleqr station.

The failure of this relay to reset resulted in the inability of DG 1A to provide any output voltage. Start attempt #992 is considered a valid failure due to the fact that if it had occurred when the DG was required for a design basis event (BO or LOCA) it would not have been available to 4

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I s SPECIAL REPORT CATAWHA NUCLEAR STATION DOCKET NO. 50-413 DIESEL GENERA'IT)R 1A VALID FAILURE DUE TO FAILURE OF SHUTDOWN RELAY IN FIELD FLASil CIRCUIT PIP 1-C93-1069 provide power to the required loads. Subsequent start attempts #993 and

1. 994 are classified as invalid failures since they occurred during the ,

troubleshooting process. '

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