ML17223A655

LER 90-005-00:on 900418,startup Transformer Feeder Breaker 1B Tripped on Overcurrent.Caused by Equipment Failure. Transformers Tested to Ensure No Damage occurred.W/900515 Ltr

ML17223A655
Person / Time
Site:	Saint Lucie
Issue date:	05/15/1990
From:	Sager D, Weeks J FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-90-176, LER-90-005-01, LER-90-5-1, NUDOCS 9005220165
Download: ML17223A655 (5)

Text

ACCELERATED DISTRIBUTION DEMONS TION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9005220165 DOC.DATE: 90/05/15 NOTARIZED: NO DOCKET FACIL:50-335 St. Lucie Plant, Unit 1, Florida Power & Light Co. 05000335 AUTH. NAME . AUTHOR AFFILIATION WEEKS,J.W. Florida Power & Light Co.

SAGER,D.A. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 90-005-00:on 900418,EDG automatic start due to loss of electrical bus caused by breaker failure.

t W/9 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR TITLE: 50.73/50.9 Licensee Event Report (LER),

ENCL A SIZE:

nciden~t Rpt, etc.

NOTES RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD 1 1 NORRIS,J 1 1 INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 DEDRO 1 1 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB9H3 1 1 NRR/DLPQ/LHFB11 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB11 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D NRR/DST/SICB 7E

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1 1 1 1 NBRQDST7~LBBD1 1 1 NRR/DST/SRXB 8E 1

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1 RGN2 FILE 01 1 1 EXTERNAL EG &G STUART ~ V A 4 4 L ST LOBBY WARD 1 1 LPDR 1 1 NRC PDR 1 1 NSIC MAYS,G 1 1 NSIC MURPHY,G.A 1 1 NUDOCS FULL TXT 1 1 NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISHUBUTION LISTS FOR DOCUMENIS YOU DON'T NEED!

t FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF.. COPIES REQUIRED: LTTR 36 ENCL 36

P.O. Box14000, Juno Beach, FL 33408-0420 FPL MAV, 15 ~990 L-90-176 10 CFR 50.73 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Gentlemen:

Re: St. Lucie Unit 1 Docket No. 50-335 Reportable Event: 90-05 Date of Event: April 18, 1990 Emergency Diesel Generator Automatic Start due to Loss of Electrical Bus Caused b Breaker Failure The attached Licensee Event Report is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.

Very truly yours, D. A. S er Site St.

V c Lu 'lant President DAS/GRM/slh Attachment cc: Stewart D. Ebneter, Regional Administrator, Region II, USNRC Senior Resident Inspector, USNRC, St. Lucie Plant 9005220165 900515 PDR ADOCK 05000335 PDC an FPL Gcoup company

fPl /@caela ot US. RUCLEAR REG'AATORY COMMISSION IRC C~ %i APPROVED OMS NO. 31504104 3 45)

LICENSEE EVENT REPORT (LER) EXPIRES 8/31/85 FACILITYNAME (1) DOCKET NUMBER (2 PAGE 3 St. Lucie Unit 1 0 500033 510 0 3 TITLE (4)

Emergency Diesel Generator Automatic Start Due to Loss of Electrical Bus Caused by Breaker Failure EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED(6)

MONTH DAY YEAR YEAR. MONTH DAY YEAR FACILITYNAMES DOCKET NUMBER(S)

NU N M NIA 0 5000 041890 9 0 0 0 5 0 0 0 5 1 5 9 0 THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR OPERATING 5 Check one or more of the followin 11 MODE (9) 20.402(b) 20.405(c) 50.73(a)(2)(iv) 73.71(b)

POWER 20.405(a)(1) (I) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)

LEVEL

(<<) 0 0 0 20.405(a) (1 )(Ii) 50.36(c)(2) 50.73(a)(2)(vll) OTHER (Specify ln Abstract 20.405(a) (1 )(lli) 50.73(a)(2) (I) 50.73(a)(2)(viil)(A) below and in Text 20.405(a)(1)(iv) 50.73(a)(2) (ii) 50.73(a)(2)(vill)(B) NRC Form 366A) 20.405(a)(1)(v) 50.73(a)(2)(ill) 50.73(a)(2)(x)

LICENSEE CONTACT FOR THIS LER (12)

NAME AREA CODE J. W. Weeks, Shift Technical Advisor 4 0 7 465- 3 550 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 13 CAUSE SYSTEM COMPONENT MANUFAC- TURER REPORTABLE TO NPRDS GAUSF SYSTFM COMPONFNT MANUFAC- TURER R(PORTABLE 0 NPRDS B E L B K R 1 2 0 I I SUPPLEMENTAL REPORT EXPECTED 14 EXPECTED SUBMISSION YES (Ifyes, complete EXPECTED SUBMISSION DATE) NO DATE (15)

ABSTRACT (Limit to 1400 spaces. I.e. approximately fifteen single-space typewritten lines)(16)

At 1105 on April 18, 1990, while St. Lucie Unit1 was in Mode 5, the Auxiliary Transformer breaker to the 1B2 4160V bus (breaker no. 20301) was being racked in to prepare for the planned startup of the unit. When the breaker control fuses were installed, the breaker closed in. This caused the 1B Startup Transformer to be shorted to the Main Generator and the Main Transformers, which were deenergized. As a'result, the 1B Startup Transformer feeder breaker to the 2B4 4160V bus (breaker no. 2-20705) then tripped on overcurrent. Power was lost to the 'B'ide electrical buses.

The 1B Emergency Diesel Generator then started and'picked up the 1B3 emergency bus loads as designed.

The root cause of the event was equipment failure. Excessive wear on the breaker closing mechanism mounting plates allowed the closing latch mechanism to move excessively which prevented the closing latch from performing its designed function. The charging spring motor charged the closing spring but the closing latch would not latch the mechanism. This allowed the breaker to close in as soon as the closing spring was charged.

Corrective actions taken were to test the 1B Startup Transformer, the Auxiliary Transformers, the Main Transformers, and the Main Generator to ensure no damage had occurred to them, and to remove the Auxiliary Transformer breaker and ship it to the repair vendor for troubleshooting and repair. Other similar breakers were inspected. Four were shipped to the vendor for repair.

fPL Saca+4o tl Ua. NNXEAR REGUlATORY COMMISSION AC Fore X4 APP ROVEO 0MB NO. 315001/M (N+

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION EXPIRES 8/31/85 FACILITYNAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR EQUENTIAL REVISION NUMBER  : NUMBER St. Lucie Unit 1 0 500 033 59 0 0 0 5 0 0 0 2 0 3 TEXT (Ifmore space is required, use additional NRC Form 366A's) (1 7)

At 1105 on April 18, 1990, St. Lucie Unit 1 was in Mode 5 after completing a refueling outage. Plant personnel were racking the 41 60V circuit breaker number 20301 into its cubicle in preparation for plant startup. This breaker is the Auxiliary Transformer (EIIS:EL) supply breaker to the 1B24160V switchgear. This breaker is closed in by the plant operators when the unit is on line and on-site power is being transferred from the off-site supplied Startup Transformers (EIIS:EA) to the Auxiliary Transformers powered from the unit Main Generator (EIIS:EL).

At the time the breaker was being racked in, the Main Generator was deenergized and was not spinning. The Main Transformers (EIIS:EL) and Auxiliary Transformers were also deenergized. After the breaker was installed in its cubicle, the control fuses for operating the breaker were installed. At this time the spring charging motor charged the closing spring, but the latching mechanism failed to latch open the closing spring and the breaker closed. No'operating switches were manipulated. When the breaker closed, the Auxiliary Transformer became energized from the Startup Transformer, as did the Main Generator and Main Transformers. This caused a large in-rush of current which caused the 1B Startup Transformer feeder breaker number 2-20705 to trip on overcurrent. Subsequently all 41 60V power to the 'B'ide electrical buses was lost. The 1B Emergency Diesel Generator (EIIS:EK) started on detection of an undervoltage condition on the 1B3 emergency bus (EIIS:EB) and the Diesel Generator picked up the emergency bus loads as designed. The faulty Auxiliary Transformer breaker, which was now deenergized, was then racked back out of its cubicle.

Troubleshooting commenced to determine whether damage had occurred to the Startup Transformer or its feeder breaker. At 1345 on April 18, 1990, it was determined that the Startup Transformer breaker had operated correctly and was not damaged. At this time the breaker was closed in which restored normal power to the non-emergency buses. The 1B Diesel Generator was paralleled to the grid and was then secured. Off-site power was then carrying all buses in the normal configuration.

The faulty breaker was bench tested and the charging motor operated but the breaker failed to latch open when control power was provided to the breaker. This had not occurred when it was bench tested prior to installation in its cubicle. The breaker was then shipped to the repair vendor for further troubleshooting and repair.

The root cause of the event is due to equipment failure. The front plates and splined bearings on the breaker frame are the same size for larger breakers (Westinghouse model nos. 50DHP350 and 75DHP500) as for smaller breakers (Westinghouse model no. 50DHP250). The larger breakers have larger charging motors and charging springs which induce more force on the mounting frames.

Therefore, after repeated spring chargings, the holes in the breaker frame where the plates and bearings are press-fit mounted became enlarged, allowing some movement to take place. This movement was enough to cause the closing latch to fail to engage when the closing spring was charged, thus allowing the breaker to close inadvertently.

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~ )Cl)CCC) LICENSEE EVENT REPORT (LER) TEXT CONTINUATION EXPIRES 8/3) )85 FACILITYNAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

YEAR QI@NTIAL RF Vl)IP St. Lucie Unit 1 05000335 9 0 0 0 5 0 0 0 3 0 3 TEXT (lfmore space is requIred, use additional NRC Form 366A's) (1 7)

The Auxiliary Transformer breaker was racked into its cubicle in preparation for the unit startup. It had been previously bench tested and was in working order. However, when its control fuses were installed, it malfunctioned and closed in. This caused the Main Generator, Main Transformers, and Auxiliary Transformers to become energized from the 1B Startup Transformer. An overcurrent condition resulted causing the Startup Transformer breaker to trip. This then caused loss of power to the 'B'ide electrical buses. The 1B Emergency Diesel Generator started on undervoltage on the 1B3 emergency bus. The Diesel Generator picked up the 1B3 bus as designed and power was maintained on the emergency bus.

The Auxiliary Transformers and their respective switchgear are not safety related components.

However, the failure of this breaker caused the loss of electrical power to the 'B'ide, including the safety related emergency bus; thus forcing the 1B Emergency Diesel Generator to start, reenergize the 1B3 bus, and perform its designed safety function. Therefore this event is reportable to the NRC under 10CFR50.73(a)(2)(iv) as any event or condition that resulted in manual or automatic actuation of any Engineered Safety Feature.

Due to the fact that the 1B Emergency Diesel Generator started and loaded the 1B3 emergency bus as designed, and that the 'A'ide electrical buses were not affected; the health and safety of the public was not endangered at any time during this event.

The 1B Startup Transformer, its feeder breaker, Auxiliary Transformers, Main Transformers, and Main Generator were tested to ensure no damage had occurred.

r The faulty breaker was removed and sent to the repair vendor for troubleshooting and repair. The vendor recommended spot welding the bearings in place on the breaker frames to prevent future movement. This was reviewed by FPL Engineering and was approved. The breaker was repaired.

All other similar breakers on Unit 1 were inspected. Four were found to exhibit the same wear characteristics. These breakers were found to function properly;.however, they were sent to the repair vendor for rework to preclude future failures.

All similar breakers on Unit 2 will be inspected during the next refueling outage scheduled for September, 1990.

Westinghouse circuit breaker model nos. 50DHP350 and 75DHP500.

Failures of this type had been previously identified by the repair vendor during the overhaul of these breaker models at other facilities. No inspection criteria is provided in the Manufacturer's Technical Manual for checking for excessive axial or radial movement of the bearings.

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