ML20206A063

Special Rept:On 870302,during Operability Test,Diesel Generator 2A Failed to Achieve 4,160-volt Ac within 11 as Required by Tech 3.8.1.1.2.Caused by Failure of Capacitor in exciter-voltage Regulator Output Circuits

ML20206A063
Person / Time
Site:	Mcguire
Issue date:	04/01/1987
From:	Tucker H DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 8704070406
Download: ML20206A063 (4)

Text

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DUKE POWER GOMPANY P.O. box G3189 CHARLOTrE, N.C. 28949 HAL B. R'CKER Tatzenown vuos caussasse (704)373-4531 stotaan enamectioso April 1, 1987 U.S. Nuclear Regulatory Connaission Document Control Desk Washington, D.C. 20555

Subject:

McGuire Nuclear Station Docket No. 50-370 Diesel Generator Failure Special Recart Technical Specification 3.8.1.1.3 and 6.9.2 Gentlemen:

4 Please find attached a Diesel Generator failure report submitted pursuant to Technical Specification (T.S.) 6.9.2 as specified in T.S. 4.8.1.1.3. The report I

concerns a valid failure of Diesel Generator 2A due to the failure of a capacitor.

This event is considered insignificant with respect to the health cnd safety of the public.

Very truly yours, L

Qc Hal B. Tucker SEL/19/jgm I Attachment xc: Dr. J. Nelson Grace American Nuclear Insurers Regional Administrator, Region II c/o Dottie Sherman, ANI Library U.S. Nuclear Regulatory Commission The Exchange, Suite 245 101 Marietta St., NW, Suite 2900 270 Farmington Avenue Atlanta, GA 30323 Farmington, CT 06032 Mr. Darl Hood INPO Records Center U.S. Nuclear Regulatory Commission Suite 1500 '-

Office of Nuclear Reactor Regulation 1100 circle 75 Parkway Washington, D.C. 20555 Atlanta, CA 30339 Mr. W.T. Orders M&M Nuclear Consultants l NRC Resident Inspector 1221 Avenue of the Americas McGuire Nuclear Station New York, NY 10020 8704070406 070401 PDR ADOCK 00000370 S I PDR

Diesel Generator 2A Valid Failure Due to a Failed Capacitor in the Exciter-Voltage Regulator INTRODUCTION:

On March 2,1987, at 0910, during the performance of an operability test, Diesel Generator (D/G) 2A failed to achieve 4160 VAC within 11 seconds as required by Technical Specification (TS) 3.8.1.1.2. This was a valid test and was the sixth valid failure of a Unit 2 D/G in the last one hundred valid tests. The cause of the failure was investigated and a circuit board in the Exciter-Voltage Regulator was replaced. The baseline and operability tests were then performed successfully and the D/G was declared operable at 2250 on March 3. Later, while evaluating the circuit board in the shop, a capacitor in the output filter circuit for the Exciter-Voltage Regulator was discovered to have failed which would have slowed the generator field flashing control circuit.

Unit 2 was in Mode 1, Power Operation, at 100% power at the time of this incident.

This incident has been attributed to the failure of the capacitor.

BACKGROUND:

Each unit at McGuire Nuclear Station has two independent D/Gs which, as a part of the Essential Power System, provides standby AC power to the equipment required to safely shut down the reactor in the event of the loss of normal power. The D/Gs also supply power to the safeguard equipment as required during a major accident coincident with a loss of normal power (blackout).

Each D/G unit consists of a sixteen cylinder Nordberg diesel engine connected to a 4 KV generater manufactured by Electric Products Division of Portec Inc.

A governor and an Exciter-Voltage Regulator are interconnected to control the D/G in both automatic and manual modes. An emergency override feature func-tions to reset the manual mode to the automatic mode when an Engineered Safety Features (ESF) actuation occurs. When the D/G is shut down, the governor and Exciter-Voltage Regulator are automatically reset to the automatic mode and to the correct emergency use settings.

The Exciter-Voltage Regulator controls the generator output by varying the current applied to the generator field windings. Several inputs are supplied to the logic circuits, an appropriate field flashing current is calculated, and the output is then applied to the generator field windings.

DESCRIPTION OF EVENT:

D/G 2A was started at 0910 on March 2,1987, for a routine operability test (start No. 546, valid failure). It accelerated normally but did not reach 4160 VAC until 11.3 seconds had elapsed. Because all other indications were normal including the 8.5 seconds required to reach 95% speed, it was suspected that the Events Recorder which measures the D/G response time was in error. i I

The Events Recorder was evaluated and the indicated time for the D/G startup was determined to be correct. No discrepancy could be found in the Events Recorder time or with its operation; therefore, D/G 2A was declared inoperable 1

at 1013. The remaining essential power sources were verified as operable by 1050 in accordance with TS 3.8.1.1. A work request was written to investigate and correct the problem.

At 1514 on March 2, D/G 2A was started to begin troubleshooting. The time to reach 4160 VAC was 11.9 seconds but again, no other abnormalities were ob-served and no apparent cause was observed. Test recorders and other test instrumentation were installed and on March 3, D/G 2A was started twice. The times to reach 4160 VAC vcre 9.9 and 9.8 seconds respectively with no abnor-malities noted. After evaluating the test data, an intermittent malfunction in the Exciter-Voltage Regulator circuits was determined to be the probable cause and the circuit board containing those circuits was replaced. D/G 2A was started again for the Diesel Generator Voltage Regulator Benchmark Com-parison Test, which exercises the D/G through voltage and load transients and benchmarks the performance of the Exciter-Voltage Regulator. D/G 2A achieved 4160 VAC in 10.2 seconds, which is within its historical response time of 10.0

+/- 0.3 seconds.

The operability test was successfully run at 2055 on March 3, (start No. 551, Valid Success) and D/G 2A was declared operable at 2250. The subsequent two operability tests were both successful with the time to reach 4160 VAC at 10.0 seconds in both cases.

A subsequent examination and test on the Exciter-Voltage Regulator circuit bocrd found one failed capacitor in the output filter circuit. Two other capacitors also gave failure indications on the tester, but the tester could not be connected as required to do a confirming test without dismantlinF the circuit board. This was not done because the circuit board will be sent back to the vendor for a failure analysis and the circuit board must be intact for a thorough analysis. The failure of any of these capacitors causes an unpre-dictable response in the output signal controlling the generator field flash-ing currents.

CONCLUSION:

D/G 2A was inoperable from 1013 on March 2 to 2250 on March 3, a total of 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> and 37 minutes. The valid failure during start attempt number 546 was the sixth valid failure in the last one hundred valid starts on Unit 2 D/Gs.

The test frequency at the time of this failure was every three days and this frequency did not change as a result of this failure. During the time D/G 2A was inoperable, D/G 2B was started five times to verify the operability of the essential power sources in accordance with TS 3.8.1.1.

This incident has been attributed to the failure of the capacitor (Model number 210B1C106M) in the Exciter-Voltage Regulator (Basler Co. P/N 32101-102) output circuits. A failure of this capacitor can cause unpredictable results and in this incident it delayed the response time of the generator by under- i correcting the generator field currents. '

A review of past McGuire reports indicates there was one previous valid D/G start failure where diodes on the Exciter-Voltage Regulator circuit card had f ailed. Since the failed components are not the same as in this incident, even though they are on the Exciter-Voltage Regulator circuit board, this incident is considered non-recurring.

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This incident is Nuclear Plant Reliability Data System (NPRDS) reportable. A search of the NPRDS dats base did not reveal any other incidents of failed capacitors related to emergency diesel generator regulators. Failures of several other types of components 11 regulators were reported, but there were no indications of a trend with either the components or the regulators as a whole.

ADDITIONAL CORRECTIVE ACTIONS:

None SAFETY ANALYSIS:

The conditions for operation of the D/Gs are specified in the TSs and provide for degraded system conditions by placing appropriate restrictions on con-tinued operation of the unit commensurate with the level of degradation.

These TSs consider the Essential Power System as a whole, and the conditions are imposed on a system basis, i.e. combinations of D/Gs and offsite power sources constitute the minimum system requirements.

The operability of the power sources is consistent with the initial condition assumptions of the Final Safety Analysis Report (FSAR) safety analyses. At least one redundant set of onsite AC and DC power sources and akscciated distribution systems must be operable during accident conditions coincident with an assumed loss-of-offsite power and single failure of the other onsite AC source. The AC and DC source allowable out-of-service times are based on Regulatory Guide 1.93, " Availability of Electrical Power Sources", December 1974. When one D/G is inoperable there is an additional action requirement to verify that all required systems, subsystems, trains, components and devices that depend on the remaining operable D/G as a source of emergency power are also operable, and that the steam-driven auxiliary feedwater pump is operable.

This requirement is intended to provide assurance that a loss-of-offsite power event will not result in a complete loss of safety function of critical s systems during the period one of the D/Gs is inoperable.  ;

During the period when D/G 2A was inoperable, the Train B systems were verified to be fully operable on a continuous basis along with both offsite power sources. If an accident had happened during the period of time D/G 2A was inoperable, those systems and components necessary to mitigate the accident were available and operable. D/G 2A was inoperable for approximately half of the time allowed by the TSs.

There were no personnel injuries, personnel overexposures, or releases of radioactive material as a result of this incident.

The health and safety of the public were not affected by this incident.

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