ML19332F505

LER 89-013-00:on 891112,4 Kv Bus 1A Power Supply Breaker Tripped on Phase overcurrent,de-energizing Emergency Bus 1A. Caused by Incorrect Tap Setting on Overcurrrent Relay.Relay Taps Reset & Breaker replaced.W/891211 Ltr

ML19332F505
Person / Time
Site:	Beaver Valley
Issue date:	12/12/1989
From:	Noonan T DUQUESNE LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-013-01, LER-89-13-1, ND3MNO:2000, NUDOCS 8912150100
Download: ML19332F505 (5)

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Telephone (417) 303-6000 Nuclear Group '

P O Don 4 Shippmpport. PA 15077 0004 December 11, 1989 ND3MNO:2000 Beaver Valley Power' Station, Unit No. 1 Docket No. 50-334, License No. DPR-66 LER 89-013-00 United States Nuclear Regulatory Commission '

Document Control Desk Washington, DC 20555 Gentlemen:

In accordance with Appendix A, Beaver Valley Technical Specifications, the following Licensee Event Report is submitted: -

LER 89-013-00, 10 CFR 50.73.a.2.iv, " Diesel Generator Autostart on Bus'Undervoltage".

Very truly yours, T. P. N onan General Manager '

Nuclear Operations cj Attachment l

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Dec:mber 11, 1989

• ND3MNO:2000 Page two cc: Mr. William T. Russell Regional Administrator United States Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406 C. A. Roteck, Ohio Edison Mr. Peter Tam, BVPS Licensing Project Manager United States Nuclear Regulatory Commission Washington, DC 20555 J. Beall, Nuclear Regulatory Commission, BVPS Senior Resident Inspector Dave Amerine Centerior Energy 6200 Oak Tree Blvd.

Independence, Ohio 44101 INPO Records Center Suite 1500 1100 Circle 75 Parkway Atlanta, GA 30339 G. E. Muckle, Factory Mutual Engineering, Pittsburgh Mr. J. N. Steinmetz, Operating Plant Projects Manager Mid Atlantic Area Westinghouse Electric Corporation Energy Systems Service Division Box 355 Pittsburgh, PA 15230 American Nuclear Insurers c/o Dottie Sherman, ANI Library The Exchange Suite 245 270 Farmington Avenue Farmington, CT 06032 Mr. Richard Janati Department of Environmental Resources P. O. Box 2063 16th Floor, Fulton Building Harrisburg, PA 17120 Director, Safety Evaluation & Control i Virginia Electric & Power Co.

P.O. Box 26666 One James River Plaza  !

Richmond, VA 23261 }

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sv.wa oh YtB I!! ree tw owt. tulCTED Substr55 TON DA TEP No l l l Ant.ACTu,,,,,,,,, ,.. . - ,an -,. -.,,,.-r- *- nei On 11/12/89, operators started the "A" Reactor Coolant Pump.

Approximately 1.5 seconds after the pump started, the 1A 4KV bus power supply breaker tripped on phase overcurrent. This de-energized the 4KV 1AE Emergency bus, which is supplied from the 1A bus. The #1 Diesel Generator started and reenergized the IAE bus. All required components sequenced back onto the bus, except for 480VAC Motor Control Center (MCC) 1-E9. Operators manually reenergized MCC 1-E9. After verifying no bus fault existed, operators reenergized the 1A bus and realigned the 1AE bus to its normal supply. The bus trip was due to an incorrect tap setting on an overcurrent relay, following the relay calibration. The relay taps were reset. A Human Performance Evaluation is being conducted to further investigate this event. MCC 1-E9 did not reenergize due to a fault in its supply breaker. The breaker was subsequently replaced and the vendor contacted to investigate the failure. There were no safety implications due to this event. A Diesel Generator reenergizing an Emergency Bus is covered in the Beaver Valley Unit 1 UFSAR Section 8.5.2 "AC Emergency Power System". Although MCC 1-E9 failed to sequence onto the bus, operators manually energized the affected components.

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Olo al? 013 n,a a n, wn maa. ~ ,awa nc re ma mm Description of Event On November 12, 1989 at 1238 hours0.0143 days <br />0.344 hours <br />0.00205 weeks <br />4.71059e-4 months <br />, while the plant was in Operational Mode 5 (Cold Shutdown), the "A" Reactor Coolant Pump j was started as part of the Reactor Coolant Fill and Vent Procedure (OM 1.6.4.F). Approximately 1.5 seconds after the pump was started, the 1A 4KV bus Offsite Power Supply breaker tripped on phase overcurrent. This de-energized the 1A bus and the 1AE 4KV Emergency bus, which is powered from the 1A bus.

The #1 Emergency Diesel Generator autostarted and reenergized the IAE bus. All required components sequenced back onto the bus, with the exception of Motor Control Center (MCC) 1-E9. MCC 1-E9 supplied power to several components including the control Room and Switchgear emergency ventilation systems and the backup supply to the Train A 120 VAC Vital Busses. The Train A 120VAC Vital Busses were not lost since they have two sources of backup power (the 125VDC station batteries and MCC 1-E13, which was sequenced on following the diesel generator start). The MCC 1-E9 supply breaker was found to be tripped. The breaker was reset and re-closed at 1242 hours0.0144 days <br />0.345 hours <br />0.00205 weeks <br />4.72581e-4 months <br />, reenergizing MCC 1-E9without incident.

After the 1A bus was checked for faults, it was restored to its normal power supply (Offsite Power) at 1310 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.98455e-4 months <br />. At 1442 hours0.0167 days <br />0.401 hours <br />0.00238 weeks <br />5.48681e-4 months <br />, the "A" Reactor Coolant Pump was bridged and meggered.

The motor was verified to be free of electrical faults.

Cause of Event An investigation determined that the relay coil taps for the 1A 4KV B-Phase Overcurrent relay (Westinghouse type CO-6) had been incorrectly restored. Prior to adjusting the setpoint, the calibration procedure has the relay coil taps moved so that the relay can be calibrated using low currents. After the setpoint is adjusted, the procedure requires the taps to be restored to their high current sotting. During the relay calibration, the >

technician failed to restore the tap positions. This resulted in the relay having a significantly lower than required trip setpoint and caused it to trip due to the normal Reactor Coolant Pump starting current surge.

The supply breaker (General Electric type AK-3A-25) for MCC 1-E9 tripped due to an internal fault when the MCC was sequenced i onto the bus. The vendor examined the breaker and found l insufficient tripper arm cicarance. This clearance is set by the vendor in the factory and not adjusted by the end user, l

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f Corrective Actions The following corrective actions are being taken as a result of this event:

1. The B-Phase Overcurrent relay taps were restored to their correct positions.

2. A Human Performance Evaluation System (HPES) study is being performed to further evaluate this event.

3. The involved technician was counseled.

4. The Electrical Maintenance department will review this event with all relay technicians.

5. The faulted supply breaker for MCC 1-E9 was replaced with a spare. The spare breaker has been tripped checked to verify correctly operate.

Safety Analysis There were no safety implications due to this event. Although the relay setpoint error resulted in actuation at a lower than desired setpoint, the system components performed as designed on a loss of power to the emergency bus. A Diesel Generator reenergizing an Emergency Bus after loss of normal AC power is covered in Beaver Valley Unit 1 Safety Analysis (UFSAR Section 8.5.2, "AC Emergency Power System"). Although MCC 1-E9 was not automatically reenergized, operators manually reenergized it approximately two minutes after normal sequencer energization should heve occurred. MCC 1-E9 supplies power to several components including the Control Room and Switchgear emergency ventilation systems and the backup supply to the Train A 120 VAC Vital Busses. The Train A 120VAC Vital Busses were not lost since they have two sources of backup power (the 125VDC station

i. batteries and MCC 1-E13, which was sequenced on following the diesel generator start).

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