ML17228A917

Special Rept:On 941028,EDG Failure Occurred Due to Burned Through Wire from Magnetic Amplifier Terminal Block to Field.Wire Repaired & Relanded to Terminal Block

ML17228A917
Person / Time
Site:	Saint Lucie
Issue date:	11/23/1994
From:	Sager D FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-94-294, NUDOCS 9411300214
Download: ML17228A917 (4)

Text

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(:ECCEI.ERATED Rl DS I'ROC!:.SSIX I A REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:.9411300214 DOC DATE: 94/11/23

~ NOTARIZED: NO DOCKET FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power & Light Co. 05000335 AUTH. NAME AUTHOR AFFILIATION SAGER,D.A. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Special rept:on 941028,EDG failure occurred due to burned through wire from magnetic amplifier terminal block to field. Wire repaired & relanded to terminal block.

DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR ! ENCL TITLE: 50.73/50.9 Licensee Event Report (LER), Tncident Rpt, etc. L SIZE: 9 NOTES RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 PD 1 1 NORRIS,J 1 1 INTERNAL'CRS 1 1 '

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PLE:XSE fkELP L'S TO REDL'CE iVKSTE! COi'f hC'f 'I'I IE DOC!:iIEiTCOi ROI. f DESk. ROOXI Pl-37 (EXT. 504-2083 ) TO ELI illiAI'E 5'OI.'R iAi!LZFI<Oil DISTRI8L'TION LIS I'S FOR DOCI.'iII:.i'I'S YOU'Oi'"I'lED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 27 ENCL 27

Florida Power 8t Light Company, P.O. Box 128, Fort Pierce, FL 34954.0128 November 23, 1994 L-94-294 10 CFR 50.36 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Re: St. Lucie Unit 1 Docket No. 50-335 Special Report Date of Event: October 28, 1994 Emer enc Diesel Generator Failure, The attached Special Report is being submitted pursuant to the requirements of the St. Lucie Technical Specifications. This report provides notification of one valid failure of the 1B Diesel Generator.

Should there be any questions on this information, please contact us ~

Very truly yours, Qg~/g D. A. S er Vice P St. Lu i identPlant DAS/msd Attachment cc: Stewart D. Ebneter, Regional Administrator, USNRC Region Senior Resident Xnspector, USNRC, St. Lucie Plant II

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I. TITLE Valid Failure of the 1B Emergency Diesel Generator due to a Burned Through Wire from the Magnetic Amplifier Terminal Block to the Field.

II. INITIALCONDITIONS St. Lucie Unit 1 was in Mode 5 at the start of a refueling outage and St. Lucie Unit 2 was at 100% power.

III. EVENT SEQUENCE On 10/28/94 with Unit 1 in a refueling outage, plant personnel commenced Operating Procedure 1-0400050, . At 1758, a Loss of Offsite Power (LOOP) was initiated as part of the procedure and the 1A and 1B Emergency Diesel Generators (EDG) started and loaded. At 1858 the 1B EDG successfully completed the Load Rejection part of the procedure. Continuing with the procedure the 1A and 1B EDG breakers were opened and the 1A and 1B EDGs were stopped locally at 2205 with the emergency stop pushbuttons. At 2208 a LOOP was again initiated as part of the procedure and the 1A and 1B EDGs started and loaded. Offsite power was restored at 2235 and the 1A and 1B EDGs load was reduced to 500 KW.

At 2257 a utility licensed Reactor Operator in the Unit 1 control room saw 1B EDG megavars pegged low (reactive load in the lead) and load increasing. The Senior Nuclear Plant Operator (SNPO) at the 1B EDG reported smelling smoke and locally stopped the 1B EDG with the emergency stop pushbutton.

IV. CAUSE OF THE EVENT Investigation by Electrical Maintenance (EM) revealed a burned wire at a magnetic amplifier (mag-amp) terminal block. The mag-amp provides the self excitation voltage to the 1B EDG field winding. A loose connection had caused overheating and there was damage to the wire and its insulation.

The loose connection was possibly due to the use of stranded wire in a compression fitting.

Due to resistance heating losses the wire burned in two causing an erroneous voltage to the 1B EDG field excitation which resulted in a loss of regulator control.

This was a valid test/valid failure as it was terminated due to an alarmed abnormal condition that would have ultimately resulted in an EDG failure.

V. CORRECTIVE ACTIONS

1. The 1B EDG was emergency tripped by the SNPO after he smelled smoke.

2. EM personnel repaired the affected wire and relanded it to the terminal block.

3. EM personnel meggered the field current circuit, the mag-amp coils and the 1B EDG windings with satisfactory results.

4. EM personnel inspected the 1B EDG terminal blocks for similar loose connections with satisfactory results.

5. EM personnel performed the eighteen month surveillance on the 1A EDG which includes checking for loose connections.

6. Operations performed a surveillance run of the 1B EDG and declared it back in service.

7. Unit 2 EDGs do not have the same type of terminal block due to a different vendor, but will be inspected during the upcoming eighteen month surveillance.

8. FPL Site Engineering is evaluating the stranded wire/compression fitting interface.

VI. SUPPORTING INFORMATION

-This was the first valid failure of the 1B EDG in the previous twenty valid tests and the sixth valid failure in the previous eighty-nine starts (EDG run counts began 6/12/90 when Reg Guide 1.108 was implemented into the St. Lucie Unit 1 Technical Specifications). The current number of valid tests for the 1B EDG is now ninety-one.

-The 1B EDG was out of service for approximately fourteen hours until the repair could be completed and a successful surveillance test was performed.

-Due to the failure, the 1B EDG is required to be surveilled every seven days until seven consecutive failure free tests are achieved per Technical Specification 3.8.1.1, Table 4.8-1.