ML20126E875

Special Rept:On 921125,EDG D21 Output Began Erratically Increasing & Decreasing When Control Logic Converted to Isochronous Mode.Caused by Test Start Circuit Deenergizing. Damaged Wire Repaired & Shortened & Governors Inspected

ML20126E875
Person / Time
Site:	Limerick
Issue date:	12/18/1992
From:	Doering J PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9212300021
Download: ML20126E875 (3)

Text

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T.S. 6.9.2 9

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. PIIILADELPHIA ELECTRIC COMPANY I 1.!MERICK GENERATING STAl'lON P. (1 BOX 2300 SANATOGA, PA 19464-2300 December 18 , 1992 (215) 3271200 EXT, 2000 Docket No. 50-353 J. cornwo. Jn. License No. NPF-85

? $ ?NcN o $ w m s w K w U.S. Nuclear Regulatory Commission Attn Document Control Desk Washington, DC 20555

SUBJECT:

Limerick Generating Station, Unit 2 Special Report for a Nonvalid Emergency Diesel Generator Test Failure

REFERENCE:

Technical Specifications Section 4.8.1.1.3 and 6.9.2 This Special Report is submitted pursuant to the requirements of Technical Specifications (TS) Section 6.9.2 as required by TS Surveillance Requirement 4.8.1.1.3. TS Surveillance Requirement 4.8.1.1.3 requires reporting of all diesel generator failures, valid or nonvalid, within 30 days. The report is required to include the information recommended in Regulatory Position C.3.b of Regulatory Guide (RG) 1.108, " Periodic Testing of Diesel ,

Generator Units as Onsite Electric Power System at Nuclear Power Plants," Revision 1, August 1977.

On November 25, 1992, with Unit 2 at 85W power level, plant personnel were performing Surveillance Test (ST) procedure ST-6-092-311-2, "D21 Diesel Generator Operability Test Run."

While procedure ST-6-092-311-2 was in progress, the D21 Emergency Diesel Generator (EDG) output began erratically increasing and i decreasing because the control logic had converted to the isochronous mode of operation instead of droop mode while connected to the offsite electrical power grid. Steady load

• could not be maintained, therefore, the D21'EDG was shutdown by the Main Control Room operator to prevent damaging the EDG. At 1100 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.1855e-4 months <br /> on November 25, 1992, the D21 EDG was declared inoperable.

Troubleshooting was conducted on November 25, 1992, to determine the cause of the erratic electrical output on the D21-EDG. It was determined that the test start circuit had de-energized causing the EDG to revert to the isochronous_ mode of operation. A wire enclosed within the mechanical governor had rubbed against the rotating portion of the mechanical. governor. l This rubbing action wore down the insulation on the wire exposing _

the bare wire. Contact of the bare wire with the rotating g portion of the mechanical governor during the starting sequence  ;

caused an intermittent battery ground in the governor circuit. A i 0 9212300021 921E1'8' '^

PDR ADOCK 05000353 S PDR

U.S.. Nuclear Regulatory Commission D2cember 18, 1992 Document Control Desk Pago 2-previously existing Unit 2, Division 1 battery ground was present during testing and troubleshooting of the D21 EDG. The previously existing positive battery ground in conjunction with the intermittent battery ground inside the mechanical governor produced electrical currents sufficient to sporadically energize L the SB relay on initial EDG starting. Energization of the SB relay results in de-energization of the test start circuit causing the control logic to switch to the isochronous mode..

The damaged wire insulation was repaired and the wire was shortened such that it would no longer contact the mechanical governor. Procedure ST-6-092-311-2 was completed satisfactorily on the D21 CDG. The mechanical governors for the remaining three

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Unit 2 and all four Unit 1 EDGs were inspected and verified to ,

not have the same condition. The wires associated with these EDGs mechanical governors were all either routed differently or i 3

were short enough to prevent rubbing. The cause of the previously existing ground has not been able to be determined yet j and the investigation is continuing utilizing Routine Test (RT) procedure RT-1-095-900-0, " Location of Battery Grounds." The D21 EDG was declared operable on November 27, 1992 at 2200 hours0.0255 days <br />0.611 hours <br />0.00364 weeks <br />8.371e-4 months <br />. >

The D21 EDG failure was classified as a nonvalid failure using the guidance of RG 1.108, Revision 1, August 1977, Section .i

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C.2.e(2). The relay contacts that caused the D21'EDG to go into isochronous mode are bypassed in the emergency operating mode so that the D21 EDG would have fulfilled its safety function'if it had been called upon in the event of an accident. Because this event was classified as a nonvalid failure, the ST procedure'-

f requency is not required to tue changed.

The D21 EDG was declared inoperable for approximately 59 -

hours as a result of this' event. However, the D21 EDG would have provided emergency power.to the Division 1 Safeguard Bus in the -;

event of an actual loss of offsite power, except during the l period that repairs were being made (i.e., November 27, 1992, -}

1120 through 1720 hours0.0199 days <br />0.478 hours <br />0.00284 weeks <br />6.5446e-4 months <br />). . Additionally, the three remaining Unit 2 EDGs were available and would have provided adequate AC power  !

to the Unit 2 Safety Related loads in the event of an actual loss '

of offsite power, ,

L -If you have any questions, please contact =Mr.:Gil J. Madsen; at_ (215) 327-1200.

Sincerely, s

i. k "

DCSicah i

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e cc: T. T. Martin, Administrator, Region I, USNRC T. J. Kenny, USNRC Senior Resident Inspector, LGS ,

bcct D. M. Smith - 52C-7 i

D. R. Helwig - SMB1-1 G. R. Rainey - 52A-6 J. A. Muntz - SSB3-1  :

G. J. Madsen - SMB2-4 -

J. B. Cotton - 53A-1 i J. J. McElwain- SSD4-3 -

E. W. Callan - SMB3-1 R. N. Charles - SIA-1 G. J. Beck, Jr., - 52A-5 <

Secretary, NCD - 51A-13 Correspondence Release Point - SMB1-2 Commitment Coordinator - 52A-5 PA DER BRP Inspector - SMB2-4 l

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