ML20207D915

Special Rept 86-001:on 860610,emergency Diesel Generator a Failed to Start.Caused by Defective Potentiometer in Static Exciter Regulator.Potentiometer Replaced

ML20207D915
Person / Time
Site:	Hope Creek
Issue date:	07/09/1986
From:	Merritt W, Salvesen R Public Service Enterprise Group
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
86-001, 86-1, NUDOCS 8607220220
Download: ML20207D915 (5)

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O PSEG Public Service Electnc and Gas Company P.O. Box L Hancocks Bridge, New Jersey 08038 Hope Creek Operations July 9, 1986 U.S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Dear Sir:

HOPE CREEK GENERATING STATION DOCKET NO. 50-354 UNIT NO. 1 SPECIAL REPORT 86-001 This Special Report is being submitted pursuant to the require-ments of Technical Specification 4.8.1.1.3 and Regulatory Guide 1.198, Rev. 2.

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R. S. Salvesen General Manager Hope Creek Operations KMH:bar SORC Mtg.86-158 ,

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On June 10, 1986 at 1200, the A Emergency Diesel Generator was started as part of an investigation into a previcus spurious Standby Liquid Control System actuation (LER 86-028). The diesel came up to speed normally, however frequency overshot to 62HZ.

Frequency and voltage then dropped to zero. Twenty seconds after frequency indicated zero, the diesel shut down. The root cause of the start failure was a defective potentiometer in the static exciter regulator which caused governor oscillations. The erratic piston movement within the governor resulted in pressurized oil being ported in quantities greater than the makeup capacity of internal pumps. This caused the output servo piston to move to minimum fuel position shutting the fuel racks. The defective potentiometer was replaced and the diesel returned to service.

This Special Report is submitted pursuant to the requirements of HOGS Technical Specification 4.8.1.1.3 and Regulatory Guide 1.108, Revision 2 "e'Li

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IDENTIFICATION DE OCCURRENCE A Emergency Diesel Generator Start Failure Event Date: 06/10/86 Event Time: 1200 This Special Report was initiated by Incident Report 86-092 CONDITIONS PRIOR TO OCCURRENCE Plant in OPERATIONAL CONDITION 4. The A Emergency Diesel Generator was being started as part of an investigation into a previous spurious Standby Liquid Control System actuation (LER 86-028).

DESCRIPTION QE OCCURRENCE On June 10, 1986 at 1200, the A Diesel Generator was started from the main control room. Operators reported voltage increased as expected, however, frequency cvershot to approximately 62 HZ. The nuclear control operator (NCO) contacted the equipment operator (EO) stationed at the local control panel for the diesel requesting the local frequency reading. The EO reported a decreasing reading of 59.5 HZ (which was the low end of the scale). The NCO at the control room console then noticed frequency and voltage decreasing.

Approximately 20 seconds after frequency indicated zero the Diesel Generator tripped. No lockout relays tripped during generator operation, however, the GEN UNDER FREQUENCY and FUEL OIL PRESSURE LOW alarms were in and out frequently.

APPARENT CAUSE DE OCCURRENCE The root cause of the diesel start failure was defective potentio-meter in the diesel generator static exciter regulator which caused governor oscillations. The erratic piston movement within the governor resulted in pressurized oil being ported in quantities greater than the makeup capacity of internal pumps. This caused the output servo piston to collapse to the minimum fuel position shutting the fuel racks and thus shutting down the diesel.

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ANALYSIS QE OCCURRENCE Diesel Generator engine speed / load is controlled by a governing system which incorporates one mechanical and one electronic gover-nor. The machanical governor is set at a slightly higher speed and frequency than the electronic governor and thus the electronic governor will control diesel operation with the mechanical governor serving as a backup.

The electronic governor receives signals from the static exciter regulator (Figure 1). The static exciter regulator incorporates a tracking, motor-operated control potentiometer (MOC) which provides a control function in both the manual and automatic modes of operation. In the subject incident, the MOC had become uncoupled at approximately full load setting (4600V). With normal generator voltage approximately 4160 volts, the uncoupled MOC caused the automatic voltage regulator to operate out of its normal range.

When outside the normal control band, the voltage regulator is unable to respond at a proper rate to dampen system transients resulting in governor oscillations.

The start failure was the first for the A Diesel Generator. As a result of the component failure, the diesel was unavailable for 62 hours7.175926e-4 days <br />0.0172 hours <br />1.025132e-4 weeks <br />2.3591e-5 months <br />. The test frequency of the diesel will continue as monthly as this is the first failure. This surveillance frequency is in conformance with the schedule in Regulatory Guide 1.108, Position C.2.d.

CORRECTIVE ACTION The defective potentiometer was replaced with a new unit. The diesel was retested in accordance with plant technical specifications and declared OPERABLE.

This event posed no threat to the health and safety of the public.

This Special Report is submitted pursuant to the requirements of HCGS Technical Specification 4.8.1.1.3 and Regulatory Guide 1.108, Revision 2.

Sincerely, R,5,5M V R.S. Salvesen General Manager Hope Creek Operations WJM:bar SORC Mtg.86-158 g,o.M -.

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