05000265/LER-1981-010-03, /03L-0:on 810515,diesel Generator Declared Inoperable When Trouble Alarm Received & Room Found Full of Smoke.Caused by Control Power Ground Fault.Ground & Damaged Components Repaired

/03L-0:on 810515,diesel Generator Declared Inoperable When Trouble Alarm Received & Room Found Full of Smoke.Caused by Control Power Ground Fault.Ground & Damaged Components Repaired

ML20009B568
Person / Time
Site:	Quad Cities
Issue date:	06/10/1981
From:	Dunesia Clark COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20009B557	List: 05000265/LER-1981-010, Forwards LER 81-010/03L-0 05000265/LER-1981-010-03, /03L-0:on 810515,diesel Generator Declared Inoperable When Trouble Alarm Received & Room Found Full of Smoke.Caused by Control Power Ground Fault.Ground & Damaged Components Repaired
References
LER-81-010-03L-02, LER-81-10-3L-2, NUDOCS 8107160301
Download: ML20009B568 (1)

LER-1981-010, /03L-0:on 810515,diesel Generator Declared Inoperable When Trouble Alarm Received & Room Found Full of Smoke.Caused by Control Power Ground Fault.Ground & Damaged Components Repaired

Event date:
Report date:
2651981010R03 - NRC Website

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LICENSEE EVENT REPORT COsTROtstOCm' l

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60 61 DOCKET NUMBER 08 69 EVENT DATE 74 75 HEPORT DATE 80 g

EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h g o,2 j l At 0340 on May 15, 1981, the Control Room received a Unit Two Diesel Generator j

trouble alarm. An Operator was immediately dispatched to find the Diesel Generator l

g o,.,, l room full of smoke.

F ?nding no evidence of fire and the local alarm, " DIESEL l

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GENERATOR MOTORING" the Diesel Generator was declared inoperable. As per Technical j

Io isl L Speci fication 4.9.E., the shared Diesel Generator and all associated low pressure l

go gg y l core and containment cooling systerPs were demonstrated operable. Probable l

j7; l consequences are minimal since off-site power was available at all times and the I

i o,; i l provisions of Technical Speci fication 4.9.E. were satisfied.

E CODE S BC E COMPONENT CODE SUSC dE SUB E

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to 11 12 13 18 19 20 SEOUENTIAL OCCURRENCE REPORT REVISION LE R RO EVENT YEAR REPORT NO.

CODE TYPE N O.

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40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h li l al l The cause of this occurrence was eauirment failure.

A 125 VDC cont rol oower around l

internal to the breaker which ties the Diesel Generator to the emergency bus' l

Wyl fault The l

caused a spurious riosure of the breaker which notored the Diesel Generator.

,,,,,j Exte.sIve testing l l,j,gl corrective action was to repai r the ground and damaged components.

and inspections of the Diesel Generator were then done to prove f ull operability l

i,i i L on May 19, 1981.

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K ESCHIPTION I 21 - 1 bi @l 68 09

80. C 8107160301 810610 Daryl G Clark 399-654-2241, ext. 170 PDR ADOCK 05000265 PHONE:

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LEP NUMBER: LER/R0 81-10/03L-0 11.

LICENSEE NAME:

Commonwee'th Edison Company Quad-Cities Nuclear Power Station Ill.

FACILITY NAME: Unit Two IV.

DOCKET NUMBER:

050-265 V.

EVENT DESCRIPTION

At 0340 on May 15, 1981, the Control Room received the Unit Two Diesel Generator Trouble Alarm, RHR System 2 Supply from Emergency Diesel Alarm, 4 KV Bus Overcurrent Alarm and Diesel Generator 2 Low Frequency Alarm.

The bus 24 to 24-1 ammeter was also indicating a current in excess of 600 amperes. An Operator was immediately dispatched to the Diesel Generator room where he found the room full of smoke.

A thorough inspection revealed no evidence of a fire in the room.

The only local alarm was " Diesel Generator Motoring".

Not knowing the cause of the problem or the extent of damage, the Unit Two Diesel Generator and its associated 4 KV bus were declared inoperable. As required in Technical Speci fication 4.9.E., the 1/2 Diesel Generator and all low pressure core cooling and containnent cooling systems associated with the 1/2 Diesel were tested immediately.

Two off-site lines capable of supplying 345 KV power were available. The Uni t Two Diesel Generator to bus 24-1 ci rcuit breaker was taken out-of-service to prevent a possible spurious closure of the breaker and to allow inspection of the generator.

VI.

PR03ABLE CONSEQUENCES OF THE OCCURRENCE:

The probable consequences of this occurrence were minimal.

The Diesel Generator is designed to fast start and supply power to the Division 11 low pressure core cooling systems if off-site power is lost.

The shared Diesel Generator is a redundant system which can supply power to either unit and power Division I low pressure core cooling equipment.

The 1/2 Diesel Generator and its associated equipnent were available at all times while the Unit Two Diesel Generator was inoperable. Also, l

of f-si te power was availeble. The ability to safely shutdown and place the reactor in the cold shutdown mode was not affected as a result of this occurrence.

l Vll. CAUSE:

The cause of this occurrence has been designated as equipnent failure.

The 4 KV breaker in bus 24-1 which connects the Unit Two Diesel Generator with the emergency bus spuriously closed in, causing the bus to energize l

the generator stator and notor the generator.

The cause of the breaker i

closing in was postulated to be a ground fault in the 125 volt DC control power circuit which operates that breaker.

Four wi res inside the breaker

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Vll. CAUSE:cubicle were found to Save the insulation worn off.

One of these wires probably shorted to ground or another wire causing the breaker closing mechanism to energize, thus closing tne breaker.

Damage to the generator was limited to the three power current transformers which go to a neutral ground detector. These transformers are directly wired into the 4 KV circuit coming off the generator. The transformers had overheateJ resulting in internal damage to the transforcers, also, a lead to the primary winding of one of the transformers was burned off.

The emergency Diesel Generator is manufactured by the Electro-Motive Division of General Motors Corporation, model A-20-Cl; rated at 4160 i

volts, 452 amps, 3250 KVA. The 4 KV circuit breaker is manufactured by General Electric Company, model MC-4.76.

There have been no previous failures of this type at quad-Cities Station.

Vill. CORRECTIVE ACTION:

The immediate corrective action taken was to verify operability of the 1/2 Diesel Generator and its associated emergency bus.

Extensive inspections and tests were performed on tha generator and equipnent connected to it.

The rotor and stator were meggered and revealed no indications of faults or degraded insulation.

A visual inspection of generator internals showed signs of localized heating on the rotor pole faces and slight flaking of the insulation. The loose insulation was removed and new insulation material was applied.

New power current transformers were installed in the neutral ground detector circuit. The four wi res with worn insulation in the 4 KV breaker cubicle were replaced.

No other problems were found in the breaker cubicle. At 0957 on May 17, 1981, the Diesel Generator was successfully started and loaded to 2500 kilowatts on bus 24-1.

Vibration readings were taken with the Diesel Generator loaded and unloaded to verify no damage wat incurred in the shaf t or coupling.

Approximately 15 minutes af ter loading the generator, all generator electrical indication was lost in the Control Room. The output breaker was immediately opened and the Diesel was shutdown.

Operability of the 1/2 Diesel Generator and the associated low pressure core and containnent cooling systems were readily verified. Two off-site lines capable of supplying 345 KV power were available. The problem was found to be a failed diode in the voltage regulator circuit. The diode had probably e/erheated when the generator was motored, but had not completely failed.

The failed diode was replaced, and on May 19,1981, at 0952, the Diesel Generator was successfully started and loaded to the bus to verify operability.

To prevent recurrence, modi ficaGon M-4-2-77-21 will be installed during the next Unit Two Refueling Outage in the fall of 1981. This modification will trip the Diesel Generator to bus 24-1 breaker from loss of excitation, generator neutral voltage, generator reverse power, and overcurrent relays.

This modification will also be installed on the 1/2 Dicral Generator during the Unit Two fall Refueling Outage.

These protective tripning devices were installed on the Unit One Diesel Generator in the fall of 1980.

This modification should be adequate to p event recurrence.