U-601834, Special Rept:On 910404,during Surveillance Diesel Generator 1A Reached Required Voltage & Frequency But Failed to Close & Phase Undervoltage Relay B-C Tripped.Cause Not Determined.Racking Mechanism Will Be Inspected & Lubricated

Special Rept:On 910404,during Surveillance Diesel Generator 1A Reached Required Voltage & Frequency But Failed to Close & Phase Undervoltage Relay B-C Tripped.Cause Not Determined.Racking Mechanism Will Be Inspected & Lubricated

ML20073L619
Person / Time
Site:	Clinton
Issue date:	05/06/1991
From:	Spangenberg F ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
U-601834, NUDOCS 9105140035
Download: ML20073L619 (2)

Text

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• U 601834 v47 91(05-06)LP ILLINDIS POWER 8E.tooC CLINTON l'OWI It STATION. I'.O. ItON 078. CtlNTON, IL1 INDIS Ul727-007 N. ^1 ELEl'IlON E 12171 Ki5 bM )

May 6, 1991 Docket No. 50-461 Document Control Desk Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

Special Report: Test Failure of Division I DJesel Generator at Clinton Power Station (CPS)

Dear Sir:

CPS Technical Specification 4.8.1.1.3 requires all diesel generator failures, valid or non valid, be reported to the Nuclear Regulatory Commission (NRC) pursuant to Technical Specification 6.9.2, SPECIAL PEPORTS, within thirty days. Due to the valid failure of the Division 1 Diesel Generator (DG1A) during surveillance testing on April 4, 1991, this SPECIAL REPORT is being submitted in accordance with the CPS Technical Specifications to provide the information required by Regulatory Guide 1.108, Revision 1, " Periodic Testing of Diesel Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants", Regulatory Position C.3.b.

Descr_1pt ion of Event; On April 2, 1991, the Division I Diesel Generator (DCIA) was removed from service and declared inoperable to perform routine preventive maintenance. This involved electrically disabling the diesel generator, which includes racking out the DG output breaker.

On April 4, 1991, at 0410 hours0.00475 days <br />0.114 hours <br />6.779101e-4 weeks <br />1.56005e-4 months <br />, following completion of the preventive maintenance (and with the DG output breaker racked in), surveillance procedure 9080.13, "DG1A(IB) Quick Start Operability", was initiated to restore DG1A to an operable status. During the surveillance, DG1A reached the required voltage and frequency within the time specified by Technical Specification 4.8.1.1.2, but the output breaker failed to close Operators noted (at approximately 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br />) that the DG1A B-C phase undervoltage relay had tripped.

At 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br />, the operators checked the relays and noted that the trip condition had cleared. Since both the A B and B-C phase undervoltage relays must t.ip to prevent closure of the DG output breaker, failure of the DG output breaker to close was not attributable to undervoltage, No work or testing was performed between 0500 and 0545 hours0.00631 days <br />0.151 hours <br />9.011243e-4 weeks <br />2.073725e-4 months <br /> which would have caused the trip condition to clear.

A maintenance work request (MWR) D17315 was initiated to investigate the reason the output breaker failed to close. The undervoltage and auxiliary relays were removed, inspected, and recalibrated; the breaker cubicle, the control power fuses, and the breaker contacts were inspected. No discrepancies were found.

uce.i woas n osos PDR ADoCK 05000461

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g** U 601834 L47 1 8E.1000

- $1nce troubleshooting did not reveal a cause for the DG1A failure, the

-DG output breaker was racked in and the DG was tested with satisfactory results. Additionally, the diesel generator was loaded and unloaded a number of times, thus causing the output breaker to be cycled several times. This provided reasonabic assurance of the breaker's reliability.

Da April 4, 1991, at 2153 hours0.0249 days <br />0.598 hours <br />0.00356 weeks <br />8.192165e-4 months <br />, DGIA was declared operable.

Since the failure of the DG output breaker to close was not attributable to undervoltage, no discrepancies were found when inveetigating the potential cause, and the breaker subsequently functioned properly, no cause for the breaker failure can be ascertained. The cause may have q been a failure of the breaker to be completely engaged due to a problem j vith the breaher racking mechanism, but as previously stated, the breaker subsequently functioned properly.

Corrective Actions Although proper functioning of the breaker has been verified as described above, a maintenance request has been initiated to inspect and r lubricate the racking mechanism for the DG1A output breaker to ensure its proper-functioning in the future. This work will be completed when 3 DGIA is next removed from service for a Division I outage. The next Division I outage is currently scheduled for October 1991. 1 Test Intervals ,

The April 4, 1991 failure was the sixth failure in the last 100 tests ,

and the first-failure in the last twenty tests. Technical Specification ,

Table 4.8.1.1.2 1, requires the testing frequency to be increased from at least once per 31 days to at least once per 7 days when the number of ,

failures is greater than or equal to two in the last twenty, or five in the last 100 tests. Therefore, DG1A is, and will be, tested weekly until seven consecutive failure-free demands have been performed.

This letter satisfies the requirement of CPS Technical Specifications 4.8.1.1.3 and 6.9.2 for issuing a SPECIAL REPORT for diesel generator ,

failures.

Sincerely yours.

[ t Y ) c J [ 4 %ttw .h F. A. Spangenberg, III Manager, Licensing and Safety TSA/alh l

-cc: NRC Clinton Licensing Project Manager ~

NRC Resident Office NRC Region III, Regional Administrator j Illinois Department of Nuclear Safety 1

i l

• Per NRC letter dated 1/25/91, one particular test performed on May f i

15, 1990, is not included in this total.

i I

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