05000029/LER-1990-001, :on 900308,bus Tie Breaker Tripped Unexpectedly When Breaker for HPSI Pump Manually Tripped as Part of Surveillance Testing.Cause Could Not Be Determined.Crossbar Buffer Assembly Readjusted

:on 900308,bus Tie Breaker Tripped Unexpectedly When Breaker for HPSI Pump Manually Tripped as Part of Surveillance Testing.Cause Could Not Be Determined.Crossbar Buffer Assembly Readjusted

ML20033H004
Person / Time
Site:	Yankee Rowe
Issue date:	03/08/1990
From:	Henderson T, Mellor R YANKEE ATOMIC ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BYR-90-046, BYR-90-46, LER-90-001, LER-90-1, NUDOCS 9004130304
Download: ML20033H004 (4)

LER-1990-001, on 900308,bus Tie Breaker Tripped Unexpectedly When Breaker for HPSI Pump Manually Tripped as Part of Surveillance Testing.Cause Could Not Be Determined.Crossbar Buffer Assembly Readjusted

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(1) 10 CFR 50.73(a)(2)(iv), System Actuation
0291990001R00 - NRC Website

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Apri1 6, 1990 DYR 90-046 t

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U.S. Nuclear Regulatory Commistion Document Control Desk Washington, DC 20555 i

Subject:

Licensee Event Report No. 50-29/90-001 Loss of Power to Emergency Dus No. 1 Renults.in' Automatic Start of Emergency Diesel Generator No. 1

Dear Sir:

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In accordance with 10 CFR 50.73(a)(2)(1) and 10 CRF 50.73(a)(2)(iv), the attached Licensee Event Report is hereby submitted.

Very truly yours, h

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Timothy K'.

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(33 NSARC Chairman (YAEC)

[1] Institute of Nuclear Power Operations (INPO)

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On March 0, 1990, at 1050 hours0.0122 days <br />0.292 hours <br />0.00174 weeks <br />3.99525e-4 months <br />, wnlle in Mode 1 at 100% power, the bus tie breaker, DT-18, tripped unexpectedly when the breaker for No. 1 High Pressure Safety injection Pump was manually tripped as part of surveillance testing.

This resulted in a loss of power to Emergency Bus No.

i and the auto start of No.

1 Emergency Diesel Generator (EDG).

The second series breaker, BT-IA, tripped on undervoltage as designed. The EDG output breaker, EG-1, failed to automatically close to provide power to the de-energized bus.

The control room operator re-energized the hus by resetting and closing DT-1A and closing BT-18.

The entire sequence occurred in approximately one minute.

The NRC was notified via the ENS at 1339 hours0.0155 days <br />0.372 hours <br />0.00221 weeks <br />5.094895e-4 months <br />.

The components of the power train were inspected and functionally tested.

The root cause of BT-ID trip could not be determined during subsequent testing and inspections.

It was determined that the buffer assembly for the crossbar of EG-1 allowed excessive travel. This caused binding on the breaker's trip shaft, which prevented the trip shaft from completely resetting.

The EG-1 breaker was readjusted and the output breakers for the other two EDGs were inspected.

This inspection did not reveal a similar condition.

The inspection procedure will be revised to include inspecting for proper positioning of the buf fer assenibly.

All Technical Specification action requirements were satisfied during this event.

There was no adverse effect to the public health or safety as a result of this occurrence.

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BACKGROUND INFORMATION

EVENT DESCRIPTION On March B, 1990, at 105B hours, vihile in Mode 1 at 100Y. power, the bus tie breaker [ Ells:DKR3, BT-1B, tripped unexpectedly when No. 1 High Pressure Safety Injection (HPSI) [ Ells:BQ3 Pump's breaker (E!!SsBKR3 was manually tripped at the conclusion of surveillance testing.

This resulted in a loss of power to the No. 1 Emergency Eus (EB) [E!!S:EK) and an auto start of No. 1 Emergency Diesel Generator (EDG)[E!!StDG3. As designed, when BT-1B opened, the undervoltage relays [EllSid73 tripped BT-1 A in series with BT-18, and the EDG started.

The output voltage ef the EDG came up to 500 volts and 62 He as designed, however, the output breaker, EG-1, failed to automatically close.

The control room staff acknowledged the penalarms resulting from the loss of power to the bus and evaluated the plant parameters and equipment status indications. Recognizing that the emergency bus was de-energized, the Primary Plant Control Room Operator took the EDG restart program switch from auto to off, reset and closed the BT-1A breaker and manually closed the BT-1B breaker i

restoring power to the Emergency Bus via its normal power supply.

The entire sequence occurred in approximately one minute.

The NRC was notified via the ENS at 1339 hours0.0155 days <br />0.372 hours <br />0.00221 weeks <br />5.094895e-4 months <br />.

CAUSE OF THE EVENT

Extensive inspection and testing of the BT-18 ane; BT-1 A bus tie breakers determined the equipment was functioning properly.

All attempts to recreate the BT-1B breaker trip condition were unsuccessful. A review of operator actions determined all actions were in accordance with procedures.

The root cause of BT-1B tripping could not be determined.

The failure of EG-1 to automatically close was determined to be compression of the moveable main contact crossbar buffer assembly washers.

This was verified by the manufacture representative who was called in to assist the plant in troubleshooting.

This condition caused the main contact crossbar to become out of adjustment resulting in the breaker tripping free upon receipt of a closing signal.

This caused a binding on the breaker's trip shaft, preventing the trip shaft from completely resetting.

SAFETY ASSESSMENT

Technical Specification (TS) 3.B.2.1 Action Statement (a), which applies to Emergency Bus No.

1, requires that the inoperable redundant bus be restored to l

operable status within B hours or be in at least hot standby within the next six hours end in cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

The loads on the bus include No.

1 HPSI and LPSI pumps, Emergency Motor Control Centers (EMCC)

[EIIS:SWGR3 Nos.

3 and 5 and the normal power supply to No. 1 EMCC through a manual throw-over switch.

TS 3.8.2.1 Action Statement (b), which applies to EMCC No.

1, requires that with the non-redundant inoperable, be in at least hot l

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One of the loads on No. 1 EMCC is the rod position indication.

The action statement for 15 3.1.3.0 concerning rod position indication was exceeded by having more than one channel inoperable TS 3.0.3 applies and a one hour shutdown is required.

Since power was successfully restored within one minute the requirement for a shutdown was removed.

Two redundant Emergency Core Cooling System trains were operable during the event.

All valves powered through Emergency Bus No. I were in the position necessary to allow the system to operate as designed in the event of a accident.

Based on the above and the short duration of the loss of power there was no adverse effect on the health or safety of the public as a result of this event.

CORRECTIVE ACTION

Emergency Diesel Generator No. I was declared inoperable.

This required restoration of the equipment in 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> according to the action statement of TS 3.B.1.1.

A procedure was generated (OP-2000.248, " No, i Emergency Power Train l

Functional Test") to prepare No.

I emergency power train for inspection and maintenance activities, and to functionally retest and return the train to service. The crossbar buffer assembly on EG-1 was readjusted and the breaker was operated satisfactorily.

The events leading up to the tripping of BT-1B were performed without recurrence of the breaker trip. Emergency Diesel Generator No. I was subsequently declared operable on 3/10/90.

The output breakers, EG-2 and EG-3, for the other two EDGs were inspected and tested. There was no indication of a similar condition existing in either of these breakers.

Plant procedure OP-4506, " Inspection of ECCS Circuit Breaker No.

is being revised to improve the inspection process of these breakers by measuring the crossbar buffer assembly position.

The individuals performing this procedure will also receive training on the changes.

Since all attempts to reproduce the unexpected breaker trip were unsuccessful and the inspection of the equipment did not reveal any abnormal conditions that could have caused the trip, this failure is considered to be an isolated occurrence and no further corrective actions are deemed necessary.

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I ADDIT 10NAL INFORMATION i

Breakers DT-1B and EG-1 are both Type AK-2A-50S units manufactured by General Electric Company, i'

SIMILAR EVENTS

1 This is the first occurrence of this nature at this facility.

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