ML20029B190

Rev to RO Dtd 910205 Re Valid Failure of Div II Diesel Generator During Surveillance Testing on 910106.Caused by Failure of A-3 Relay Tachometer Due to Broken Wire.Caution Added to Vendor Manual Re Bench Testing Relay

ML20029B190
Person / Time
Site:	Clinton
Issue date:	02/27/1991
From:	Spangenberg F ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
U-601798, NUDOCS 9103060159
Download: ML20029B190 (2)

Text

J ep g' U 601798 1/.7 91 (02 2 7 )l.P

'ILLINDIS POWER euwe l

CLIN'!ON l'OWLl4 ST ATION, l' O ILOX 678. CL'N TON.111 INath 017274Ki76. 'lrLt.I'llONL (2171 HM h881 Docket No. 50 461 I%bruary 27, 1991 Document Control Desk Nuclear Regulatory Commission Vashington DC 20555 SUluCCT: Revision to Special Report Documented in Illinois Power Conmany letter U 601708

Dear Sir:

This letter corrects a discrepancy in the Special Report submitted by Illinois Power (IP) via IP Ictter U 601788, dated February 5,1991, in whic h IP reported the valid failure of the Division II diesel generator (DGila at Clinton Power Station (CPS). The valid failure, which occurred during surveillance testing on January 6,1991, was determined to be the result of a problem with the DG1B speed control electronics Troubleshooting revealed tha t. the A 3 relay tachometer (speed switch) failed due to a broken wire on one of the silicon control rectifiers. The most probabic cause of the broken wire was determined to be aging of the A 3 relay combined with the stress placed on the wire during bench testing of the relay.

IP let ter U 601788 stated that this type of f ailure was also ap;ilicable to the Division I diesel generator (DG1A), but not t o the Division 111 diet.cl generator (DC10) since the DC1C control circuitry was supplied by a dif f erent vendor than that of DCIA and D01B, This statement was made in error, Although the DG1C control circuitry was supplied by a difforent vendor, the DCIC A 3 relay is similar in design to that of DG1A and DC1B and therefore is also susceptibic to a broken wire caused by a combination of aging and stress placed on the wire during bench testing of the relay, Corrective actions have been, or are being, taken to address both causes, aging and stress, now determined to be applicabic to the A 3 relay for all three diesel generators at CPS, A caution was added to the vendor manual, which governs the bench testing of the A 3 relay for all three DGs, to ensure the ciectricians are aware of the susceptibility of the wires internal to the relay to be stressed and to break, In addition, a preventive maintenance task (PM) for each of the three DGs will be entered into the CPS PM tracking system to remove, inspect and bench test the A 3 relay every two years. This will ensure the relay is functioning correctly and that wiren and connecttons are intact not only for DGIA and DG1B but for DC1C as well. This action will be complete by May 31, 1991.

Sincerely yours, Mg F. A. Spangenb rg, III l Manager - 1.icensing 6 Safety TSA/alg 9103060159 910227 2 FDR ADOCK 05000#1 g, PDh - # (D

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U 601798 1- 1A7 91 (02 27)LP 81:,100c <

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NRC Resident Office l NRC Region III Regionni Adrainistrator  !

Illinois Departroent of Nucicar Safety ,

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