ML20116B852

Revised Special Rept SR 95-04:on 950718,EDG 1-2 Load Swings Occurred.Caused by Defective Electronic Governor Stability Potentiometer.Replaced Electronic Governor

ML20116B852
Person / Time
Site:	Diablo Canyon
Issue date:	07/22/1996
From:	PACIFIC GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20116B844	List: DCL-96-155, Revised Special Rept SR 95-05:on 950806,EDG 1-2 to Achieve Rated Output Frequency within TS Limits.Caused by Degraded Electronic Governor Performance.Replaced Electronic Governor Motor Operated Potentiometer & Electronic Governor ML20116B841 ML20116B849 ML20116B852
References
DCL-96-155, SR-95-04, SR-95-4, NUDOCS 9607300309
Download: ML20116B852 (6)

Text

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Enclosuro 2 '

PG&E Letter DCL-96-155 REVISION TO SPECIAL REPORT 95-04, EMERGENCY DIESEL GENERATOR l '

1-2 LOAD SWINGS DUE TO A DEFECTIVE ELECTRONIC GOVERNOR DEGRADED PERFORMANCE in accordance with Regulatory Guide (RG) 1.108, Section C.3.b, the following -

information is included:

1. Diesel aenerator involved: Emergency Diesel Generator (EDG) 1-2. PG&E has re-evaluated this event in accordance with the guidance of RG 1.108, Sections B and C.2.e and determined that this event was not a valid failure.

2. As of April 1L1996 the number of valid failures in the last 100 EDG l 1-2 valid tests: 3

3. Cause of event: The root cause of this event was determined to be a defective electronic governor stability potentiometer.

4. Corrective measures taken:

a. Immediate corrective action: PG&E replaced the electronic governor PG&E then successfully tested EDG 1-2 in accordance with Surveillance Test Procedure (STP) M-9A,

" Diesel Engine Generator Routine Surveillance Test."

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b. To prevent recurrence: PG&E has replaced all EDG l electronic governors.

5. Time EDG was unavailable: EDG 1-2 was cleared to investigate the cause of load swings on July 18,1995, at 2350 PDT, EDG 1-2 was returned to an operable status after successful performance of STP M-9A on July 20,1995, at 1007 PDT. Thus, EDG 1-2 was unavailable for a total of 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> and 17 minutes.

6. Current surveillance test interval: 31 days l

7. Confirmation of proper test interval: As of April 1,1996, the total l number of valid failures in the last 100 valid tests for EDG 1-2 is 3, and the total number of valid failures in the last 20 valid tests for EDG 1-2 is 0; therefore, the 31 day test interval is in compliance with the accelerated test schedule of Technical Specifications (TS)  !

Table 4.8-1. )

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9607300309 960722 PDR ADOCK 050002 5 S

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Enclosuro 2 PG&E Letter DCL-96-155

l. Plant Conditions Unit 1 was in Mode 1 (Power Operation) at 100 percent power. ,

ll. Description of Event '

A. Summary  !

In accordance with the requirements of TS 6.9.2 and 4.8.1.1.4, and l Revision 1 to NRC RG 1.108, PG&E is- submitting this revision to Special Report 95-04 concerning failure -of EDG 1-2 on July 18, 1995. ' This event was due to degraded -EDG equipment resulting in momentary load swings during -surveillance testing. Initially, PG&E conservatively determined that -this event was a valid failure pending further evaluation.

PG&E has re-evaluated this event in accordance with the guidance of RG 1.108, Sections B and C.2.e, and determined that this event  :

was not a valid failure. ,

I B. Background l l

STP M-9A', is normally performed on a 31-day testing frequency. l  ;

STP M-9A starts and runs each EDG for a minimum of one hour 1 each test. STP M-9A is performed to demonstrate proper startup to -verify that ne required voltage and frequency are automatically l attained within acceptable limits and time. This test also verifies that the automatic startup components of the diesel generator unit are operable. j l

C. Event j On July 18,1995, at 2203 PDT, EDG 1-2 was started in the droop mode for STP M-9A. After completion of STP M-9A, EDG 1-2 ran i for an additional 47 minutes at full load. At 2350 PDT, EDG 1-2 was conservatively declared inoperal iue to momentary load swings caused by degraded EDG equw..ient. The momentary load swings varied from 200 to 300 kW at full load. l 2-

Enclosuro 2 PG&E Letter DCL-96-155 PG&E has re-evaluated this event in accordance with the guidance of RG 1.108, Sections B and C.2.e, and determined that this event  ;

was not a valid failure and EDG 1-2 could have performed its intended safety function during accident conditions' for the following reasons:

1. Since the load swings were momentary, the frequency change in the isochronous mode would not be observed due to response time of the hydraulic actuator and EDG inertia.

2. Even if the 300 kW load spike duration was to exist for a longer -

period of time and result in a load change, the frequency change at the 4 kV bus with the EDG operating in the '

isochronous mode would not be larger than *0.35 Hz. Diablo Canyon Power Plant (DCPP) TS requires that the EDG maintain a frequency of 60 Hz ii.2 Hz.

On July 18,1995, PG&E entered EDG 1-2 into an accelerated testing schedule in accordance with TS Table 4.8-1. The test schedule required that STP M-9A be performed on -EDG 1-2 at ,

least once every 7 days for a total of 20 consecutive -valid tests. l On July 19,1995, PG&E replaced the EDG 1-2 electronic governor.

On July 20,1995, at 1007 PDT, EDG 1-2 was declared operable  ;

after the successful performance of STPs M-9A, " Diesel Generator '

Routine Surveillance Test;" M-9D1, " Diesel Generator Full Load Rejection Testing;" and M-9D2, " Diesel Generator Partial Load Rejection Testing." l D. Inoperable Structures, Components, or Systems that Contributed to the Event None.

E. Dates and Approximate Times for Major Occurrences

1. July 18,1995, at 2350 PDT: Event / Discovery date.

EDG 1-2 shutdown was initiated when load swings occurred. EDG 1-2 was l declared inoperable.

Enclosuro 2 PG&E Letter DCL-96-155

2. July 20,1995, at 1007 PDT: EDG 1-2 was declared l operable after successful performance of STPs M-9A, M-9D1, and M-9D2.

F. Other Systems or Secondary Functions Affected None.

G. Method of Discovery Plant personnel identified the problem during the performance of STP M-9A.

H. Operator Actions None.

l. Safety System Responses None.

Ill. Cause of the Event A. Immediate Cause The immediate cause of this event was degraded performance of EDG 1-2 equipment.

B. Root Cause The root cause of this event was determined to be a defective electronic governor stability potentiometer.

IV. Analysis of the Event Safety-related (Class 1 E) electrical loads are supplied from three 4160 V vital buses (F, G and H) for r och unit. Each vital bus can be supplied from the 500 kV switchyard, the 230 kV switchyard, the main generator, or the EDGs. The EDGs can provide power for engineered safeguards (Class 1E) motors and loads used for emergency core cooling, reactor shutdown, and other vital safety functions when the main generator and offsite power sources are not available in the event of a loss-of-offsite power or other design-basis event.

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Enclosuro 2 PG&E Letter DCL-96-155 During a design-basis event, with EDG 1-2 in a degraded condition, one bus of vital 4160 V power may not have been available for Unit 1 support.

However, EDGs 1-1 and 1-3 were available to provide power to the other two Unit i vital 4160 V buses during the time that EDG 1-2 was inoperable. Subsequent to this event, EDGs 1-1 and 1-3 successfully completed STP M-9X, " Operability Verification."

Since only two vital buses are necessary to . support DCPP accident analysis, the health and safety of the public were not adversely affected t by this event.

V. Corrective Actions )

I A. Immediate Corrective Actions

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1. The electronic governor was replaced and functionally tested.

2. The electronic governor was sent offsite for failure analysis l and refurbishment. l l

3. EDG 1-2 was successfully tested in accordance with STP M-9A, M-9D1, and M-9D2.

4. Additional testing was performed at least once every 7 days to determine and validate the cause of the degraded EDG equipment. All accelerated testing was performed in accordance with STP_ M-9A. During accelerated testing EDG 1-2 was operated for a minimum of three hours.

5. Load monitoring equipment was installed on EDG 1-2.

B. Corrective Actions to Prevent Recurrence PG&E has replaced all EDG electronic governors. l

l Enclosuro 2 PG&E Letter DCL-96-155 VI. Additional Information A. Failed Components Component: Potentiometer,0-150 kOhms Manufacturer: A&B Model Number: 202760 Type: J B. Previous Similar Events None. l