ML20214X107

Special Rept:On 870505,diesel Generator Excitation Circuitry Failed.Caused by Loose Connection of Two Leads on Bottom of Relay K1.Relay K1 Contactor & Two Damaged Leads Removed & Replaced

ML20214X107
Person / Time
Site:	Limerick
Issue date:	06/05/1987
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Russell W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
NUDOCS 8706160332
Download: ML20214X107 (5)

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PHILADELPHIA ELECTRIC COMPANY 2301 MARKET STREET P.O. BOX 8699 PHILADELPHIA PA.19101 lat s) eas.soao M. J. COONEY

. 6... 7[."[. U."... . , June 5, 1987 Docket No. 50-352 Mr. William T. Russell, Admintstrator Region I U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

SUBJECT:

Special Reporting Requirement for Diesel Generator Failures at Limerick Generating Station

Reference:

Technical Specifications 4.8.1.1.3 and 6.9.2

Dear Mr. Russell:

This special report is being submitted pursuant to the requirements of Limerick Technical Specifications 4.8.1.1.3 and 6.9.2 which state:

ELECTRICAL POWER SYSTEMS SURVEILLANCE REQUIREMENTS 4.8.1.1.3 Reports - All diesel generator failures, valid or non-valid, shall be reported to the Commission in a Special Report pursuant to Specification 6.9.2 within 30 days. Reports of diesel generator failures shall include the information recommended in Regulatory Position C.3.b of Regulatory Guide 1.108, Revision 1, August 1977. If the number of failures in the last 100 valid tests, on a per nuclear unit basis, is greater than or equal to 7, the report shall be supplemented to include the additional information recommended in Regulatory Position C.3.b of Regulatory Guide 1.108, I Revision 1, August 1977.

8706160332 870605 '

PDR ADOCK 05000352 0 S PM B

• Mr. William T. Russell June 5, 1987 Page 2 SPECIAL REPORTS 6.9.2 Special reports shall be submitted to the Regional Administrator of the Regional Office of the NRC within the time period specified for each report.

DESCRIPTION OF EVENT:

On May 5, 1987 at 0936 hours0.0108 days <br />0.26 hours <br />0.00155 weeks <br />3.56148e-4 months <br /> during the performance of the monthly operability surveillance test for the D14 diesel generator, the engine was shut down prior to synchronization to

, the 4.16 KV bus. An abnormal condition in the generator's self-excitation circuitry had been signaled by a " Diode Failure" light. The external battery field flashing relay, which provides initial generator field excitation, did not de-energize and self-excitation of the generator failed to occur when the generator output voltage exceeded 65 to 80% of normal. Two leads on the bottom of the K1 relay (AC contactor for static exciter) were found loose and discolored at the mechanical connector lugs.

The D14 diesel generator was declared inoperable and the other three diesel generators were satisfactorily run in accordance with Technical Specification 3.8.1.1.a.

The K1 relay is an ITE lighting contactor, cat. no. A143F, line 480 volts, load 277 volts and rated at 200 amperes. It is used in a BASLER static exciter regulator Model SER-CB. The D14 failure was the first failure in the last 100 valid tests. The current diesel generator test interval is 31 days which is in conformance with Technical Specification Table 4.8.1.1.2-1 and Regulatory Position C.2.d of Regulatory Guide 1.108.

. Mr. William T. Russell June 5, 1987 Page 3 CONSEQUENCES OF THE EVENT:

The D14 diesel generator was out of service for 79 hours9.143519e-4 days <br />0.0219 hours <br />1.306217e-4 weeks <br />3.00595e-5 months <br /> and 15 minutes as a result of this event. In addition to the battery field flashing resistor and the K1 relay wire connections overheating, continued operation of the D14 diesel generator would have resulted in damage to the contactor and wiring adjacent to the resistori leading to loss of all excitation and the resultant engine shutdown. Consequently the D14 diesel generator would not have been able to provide emergency power.

However, the remaining three diesel generators could have provided adequate power to ensure the safe shutdown of the plant in the event of a loss of offsite power.

CAUSE OF THE EVENT:

The cause for the failure in the generator excitation circuitry was the loose connection of the two leads on the bottom of the K1 relay. The relay's mechanical connection lugs are screw type connectors without a bearing pad on the screw. The investigation has determined that these mechanical lugs do not provide sufficient fastening of the leads to the K1 relay terminals. The two loose connections are located at terminals which supply generator derived A.C. voltage into the excitation rectifier bridges for self-excitation. Due to the voltage drop from the higher resistance caused by the loose connections, the device which senses self-excitation never picked up and the battery field flashing continued.

CORRECTIVE ACTIONS:

The K1 contactor and the two damaged leads were subsequently removed and replaced. The mechanical lugs connecting the leads to the K1 relay have been removed and replaced with compression type lugs. The D14 diesel generator was satisfactorily run on May 8, 1987.

The mechanical lugs of the other three diesel generator's K1 relays are scheduled to be replaced with compression type lugs during the current refueling outage. During the interim, the mechanical connection lugs and leads of the K1 contactor for the other diesel generators were examined for tightness and signs of

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - . - _ - _ - _ _ J

Mr. William T. Ruc00ll Juna 5, 1987 Page 4 i

burning and corrosion. All were found to be in satisfactory condition.

Should you require additional information, please do not hesitate to contact us.

Very truly yours,

, l%G

• cc: E. M. Kelly, LGS Resident Site Inspector See Attached Service List

e

-e cc: Troy B. Conner, Jr., Esq.

Benjamin H. Vogler, Esq.

Mr. Frank R. Romano Mr. Robert L. Anthony Ms. Maureen Mulligan Charles W. Elliott, Esq.

Barry M. Hartman, Esq.

Mr. Thomas Gerusky Director, Penna. Emergency Management Agency Angus Love, Esq.

David Wersan, Esq.

Robert J. Sugarman, Esq.

Kathryn S. Lewis, Esq.

Spence W. Perry, Esq.

Atomic Safety & Licensing Appeal Board Atomic Safety & Licensing Board Panel Docket & Service Section (3 Copies)

E. M. Kelly Timothy R. S. Campbell l

March 5, 1987

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