U-601970, Special Rept:On 920328,diesel Generator 1B Manually Started But Stabilized Outside TS Range of 60 + or - Hz. Caused by Failure of Power Supply for Electronic Speed Controller.Power Supply Replaced

Special Rept:On 920328,diesel Generator 1B Manually Started But Stabilized Outside TS Range of 60 + or - Hz. Caused by Failure of Power Supply for Electronic Speed Controller.Power Supply Replaced

ML20095H419
Person / Time
Site:	Clinton
Issue date:	04/24/1992
From:	Spangenberg F ILLINOIS POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
U-601970, NUDOCS 9204290382
Download: ML20095H419 (3)

Text

, , _. _

$- Ithnols Power Company u Ciinton Pw at Stwon P O. Box 678

, Climon. IL 6i727

, Tel 217 935-8881

.e-U-601970 POWER L47 - 92 (04-24 )Lp 8E.100c April 24, 1992 10CFR50.36 Docket No. 50-461 Document Control Desk Nuclecr Regulatory Commission Washington, D.C. 20555

Subject:

Special Report: Valid Failure of Division 11 Diesel Generator at Clinton Power Station (CPS 1

Dear Sir:

CPS Technical Specification 4.8.1.1.3 requires all diesel generator failures, valid or non valid, to be reported to the Nuclear Regulatory Commission (NRC) pursuant to Technical Specification 6.9.2, SPECIAL REPORTS, within thirty days. This Special Report is being subraitted as a result of a failure of the power supply for the electronic speed controller for the Division II Diesel Generator (DGlB) which was discovered on March 28, 1992. In accordance with CPS Technical Specification 4.8.1.1.3, 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 is provided below. -

Description of Event At approximately 0541 hours0.00626 days <br />0.15 hours <br />8.945106e-4 weeks <br />2.058505e-4 months <br /> on March 28, 1992, during the performance of routine refueling outage maintenance, DG1B was manually ctarted per CPS procedure 3506.01, " Diesel Generator and Support Systems (9G)," in preparation for performance of hot alignment of the fuel racks. DG1B reeched the minimum required voltage and frequency within the time specified by the Technical Specifications However, the frequency stabilized at approximately 63 Hz (which is outside the 60 +/- 1.2 ilz range required by the Technical Specifications) and engine speed could not be manually controlled from the main control room. At approximately 0543 hours0.00628 days <br />0.151 hours <br />8.978175e-4 weeks <br />2.066115e-4 months <br />, DG1B was manually shut down without being loaded. As the diesel generator was already inoperable for the planned refueling outage maintenance, the diesel generator remained inoperable until completion of the planned and corrective maintenance.

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9204290300 920424 ,] [

DR ADOCKOSOOg1 p J

.- U 601970 g.:

Troubleshooting performed under Maint enence Vork Request (MVR) D10344 )

determined that the power supply to tie governor electronic control unit  :

had failed. This resulted in DGlb enb ine speed being coutrolled by the

-backup mechanical governor. [The tandtm diesel en6 nes 1 of DG1B each utilize Woodward EGB 13P governors which are electritally controlled, proportional output actuators with an integral backup mechanical (centrifugal) governore -The EGB-13P governor is particularly sulted foc use with tandem diesel generator units since a sing 1# electric control unit can be.used with two proportional actuators connected in series with the control unit's output. This allows each actuator to receive the same current si Enal, resulting in the 94me amount of fuel being supplied to each engine, thus ensuring synchronous operation of the two diesel engines driving the common, center-mounted generator. The mechanical governor controls engine speed during startup and also functions to prevent engine runaway should the electronic control unit fail in such a manner as to call for maximum fuel. The speed setting of the mechanical gc erncr is slightly higher (approximately 5%) than that of the electrical controllar.}

Following replacement of the failed power supply, DG1B was again manually started-per CPS procedure' 3506.01. DG1B achieved the required voltage and frequency within the time specified by the Technical Specifications and l automatically maintained the voltage and frequency within the required range. The rtesel generator was successfully synchronized with effsite '

power and loaled to rated conditions. No difficulties in maintaining the frequency with?n the required range or controlling DGlB speed from the main control room.were experienced during this-subsequent operation of DG1B.

Operability of DG1B was successfully demonstrated by. performance of CPS surveillance ^ procedure 9080.01, " Diesel Generator.lA (lB) Operability -

Manual," on April 3, 1992 following completion of the planned maintenance .

activities.

CPS-has initially determined t,, thia power supply failure should be

' considered a> valid failure'per. Regulatory Guide 1.108, Regulatory Position C.2.e(8) since no work had been performed on the power supply during the planned maintenance, and since operation with the engine speed being controlled by the mechanical governor resulted in the generator frequency not being maintained vLthin the range required by the Technical Specifications. If further evaluation determines that DG1B would have been capable af assuming the required load within and for the time prescribrd

'during an emergency with engine speed being controlled by the mechanical governor, this event will no longer be considered a diesel generator L failure (valid =or non-valid).

L Corrective Ac_tions j' As discussed above, troubleshooting of this failure was conducted under MWR l: D10344. The connectors to the governor, magnetic pickup and tachometer, as well as all fuses within the control panel, were inspected. No signs of

- damage or failure were observed. Troubleshooting of the control circuit determined that the electronic governor control unit power supply had no output voltage when the proper input voltage was applied. As the fuse for l the power supply had not blown, the power supply was determined to have failed. Following replacement of the power supply, DGlB operated properly l (i.e., generator frequency was controlled within the required range, and

+ U 601970 engine-speed was able to be manually controlted from the main conttul.

room).

The'cause of the power supply _ failure has not yet been determined. The failed power supply will be cent to Woodward Governor for a failure analysis. In addition,.lP has conducted searches of the CPS maintenance history and the Institute of Nuclear Power Operations (INPO) Nuclear Plant Reliability Data System (NPRDS) and requested input from Woodward in order to determine the reliability of these power supplies. The results of the CPS maintenance history search determined that this was the first failure of this power supply at CPS, No failures were found in NPP.DS. Information obtained from Woodward indicates that the industry failure rate for this-power supply is' low; As a result, IP considers this failure to be an isolated event and no further' corrective actions are currently planned, If the failure analysis to be performed by Woodward identifies a plant-spccific root cause for the failure, IP will evaluate _the need for further corrective actions.

Test Inte rvals The failure of the electronic governor control power supply has initial'ly been classified as a valid failure. As of March 28, 1992, DGlB had experienced five valid failures in all 93 valid tests performed on DGlB, and it had experienced one valid failure in the last 20 valid tests performed on DClB. In accordance with CPS Technical Specification Table 4.8.1.1.2 1, the test frequen;y.for DC1B has been increased to at least once per 7 days.

This letter satisfies the requirements of CPS Technical Specifications 4,8;1.1.3 and 6.9.2 for submitting a Special Report for diesel generator failures.

Sincerely yours,

/

u h. >

[ 'F. A. Sp ngen rg, II l

Manager, Licensing-and Safety DAS/alh cc: NRC Clinton Licensing Project Manager NRC Resident Office l_ _ Regional Administrator, Region III, USNRC 1111nnis Department of Nuclear Safety i

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