ML20203F310

Special Rept (Spr 970002):on 971111, a EDG Declared Inoperable After Oscillations Occurred During Performance of Monthly Surveillance Test.Erratic Fuel Rack Movement Continued After Engine Unloaded

ML20203F310
Person / Time
Site:	Summer
Issue date:	12/11/1997
From:	Gabe Taylor SOUTH CAROLINA ELECTRIC & GAS CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RC-97-0251, RC-97-251, SPR-970002, NUDOCS 9712170343
Download: ML20203F310 (6)

Text

- ~

South Carolina Electric & Gas company J.To lor Jeronsvatne SC 29305 Hucleat Operations (603) 345 4344 SCE&G

. A80ARROpppey December 11,1997 RC 97 0251 Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

VIRGIL C. SUMMER NUCLEAR STATION DOCKET NO. 50/395 OPERATING LICENSES NUMBER NPF 12 SPECIAL REPORT (SPR 970002)

This Special Report is being cubmitted by South Carolina Electric and Gas Company pursuant to the requirements of Technical Specification 4.8.1.1.3, Technical Specification 6.9.2 and Regulatory Guide 1.108, revision 1. Five Emergency Diesel Generator (EDG) start f ailures (4 valid and 1 invalid) are being reported.

Failures of November 11.12 and 13.1997:

On November 11, at 0400, the "A" Emergency Diesel Genarator (EDG) was declared inoperable after load oscillations occurred during performance of the monthly surveillance test. CER 971289 was genersted to document the failure and the condition of the EDG.

The EDG was being tested at its nominal full load rating (4250 kw) when intermittent load oscillations of approximately 400 to 500 kw above and below this nominal loading were obsesed. The load oscillations were observed on both the local and control room meters and were also evidenced by fuel rack movement on the engine.

Action was immediately initiated to determine if these oscillatior2s were due to instability on the EDG or the electrical distribution grid. No anomalies were 6bserved on the grid by either VCSNS personnel or the load dispatcher. I Erratic fuel rack movement continued after the engine was unloaded (prior to shutdown). A detailed troubleshooting plan was developed, instrumentation was M%

installed and troubleshooting initiated. However, no oscillations were observs t during this troubleshooting effort.

9712170343 971211395 ,- ,

DR ADOCK 0

. Document Control Desk SPR 970002 '

RC 97 0251 Page 2 of 6  ;

Based on plant and industry experience, it was determined that this aondition was most probably due to a malfunctiori in either the electronio control unt; (EGA) or the hydraulic actuator (EGB) of the Woodward governor. Since maintenance had been performed on the hydraulle actuator during the recent refueling outage, it was believed that some debris may have been present in the actuator oil. The hydraulic actuator oil was replaced, and a maintenance run was performed satisfactorily.

The surveillance test was again performed on 11/12/97 and the oscillations reappeared after the EDG had operated satisfactorily for abort half of the test duration. An additional troubleshooting plan was developed and a governor service representative (Woodward) was dispatched for assistance.

The troubleshooting plan was impleniented on day shift on 11/12/97. The input and output sides of the EGA (electronic control) unit were instrumented to allow capture of any signal anomalies. EGA output step changes were introduced to determine the translent response of the governor. Additional ly, the EGB (hydraulic actuator) unit was run uncoupled from the EGA unit to determine EGB stability with no electrical input.

These tests were performed and for most of the test duration, the governor operated satisfactorily. However, while loaded at about 1000 kw, one single spike of about 100 kw was observed on the recorder trace. The cause of this spike could not be determined. There were no other problems observed during this troubleshooting effort.

At this time, since the problem had still not been isolated, it was conservatively decided to replace both the EGA and EGB units. The replacement EGA unit was bench tested satisf actorily in the Electric Shop in accordance with Woodward test guidelines. These EGA and EGB units were replaced on night shift and setup continued into day shift on 11/13/97. Numerous starts and shutdowns of the EDG followed to facilitate necessary governor setup adjustments. A chart recorder monitoring the replacement EGA unit inputs and outputs showed no spiking during this setup and adjustment period.

The EGA unit that was removed also passed the vendor bench test. At this point, the unit was left powered on the bench, with no input signal changes, while the output was monitored with a recorder. Random output spikes were observed. For comparison purposes, this same test was performed on another EGA unit from the warehouse. No spikes were recorded from the output of this unit.

The surveillance test was then repeated on 11/13/97, but a slightly longer governor frequency recovery time occurred, which caused a slower than required ten second start time. This resulted in the surveillance test being stopped and additional adjustments made to the governor hydraulic actuator (EGB unit). Several additional start attempts and runs were made to assure that the governor adjustments were complete.

L

' Document Control Desk SPR 970002 RC 97 0251 7 Page 3 of 6

, , +

The surveillance tests were then performed and completed satisfactorily. The EDG was declared operable at 0000 on 11/14/97. The EDG had been inoperable for 68 hours7.87037e-4 days <br />0.0189 hours <br />1.124339e-4 weeks <br />2.5874e-5 months <br />. ,

i The three surveillance test failures were determined to be valid tests and failures per Regulatory Guide 1.108. These test failures resulted in 3 failures in the Inst 20 valid  ;

tests and 4 failures in the last 100 valid tests. Since the number of failures in the last 20 valid tests for the "A' diesel generator was greater that 1, the surveillance test frequency was increased to once per 7 days.  ;

Failure of November 21,199h On November 21, at 0315, the *A" Emergency Diesel Generator (EDG) was declared inoperable after severe load oscillations occurred during performance of the surveillance test. These oscillations were much more severe than had been previously encountered, as observed by the fuel racks driving to thalt stops. The test frequency for this olesel had been increased to weekly from monthly because of the previously described test f ailures due to problems with smaller load oscillations.

During this surveillance test, the diesel started normally. During loading to it's first loading step of about 1000 kw, large load oscillations occurred. The dieselload was increased, but the load oscillations continued. At a load of about 3000 kw, it was decided not to load the diesel any further because the load oscillations were still occurring. The diesel was shutdown and CER # 971334 was written to address the problem. A representative from the govemor manufacturer, WooJward, was called to the site to provide assistanco.

Since the electronic control and hydraulic actuator (EGB) units of the governor had been replaced during the previous failure, the troubleshooting effort was initially focused on inputs to the EGA unit. This effort involved inspection of the voltage regulator potential transformers and current transformers which provide inputs to the EGA unit and included inspections of the voltage regulator panel and associated

, ele &lcal connections. Also, the test start circuit which applies droop to the governor for loading to the grid and removes droop for isochronous operation on an isolated bus was inspected to determine if the associated relays and contacts were functioning properly.

There were no problems found with the voltage regulator components. However, a degraded condition was found with the isNhronous/ droop (ID) relay. This relay had two contacts which would not change stat o (measured open whether the relay was energized or not) and high resistance was measured across several other contacts.

The contacts which had high resistance were determined to affect the speed droop

- 'Docement Control Desk

! SPR 970002 l

! RC 97 0251  !

Pa0e 4 of 6 l

oircuit in the EGA unit. Erratic operation or loss of speed droop will result in severe load oscillations when paralleled to the electrical power grid due to unstable load -  !

L sharing. The Woodward representative agreed with this assessment and conclusion. .l 1

, The ID relay was replaced, additional governor adjustments were made and additional i maintenance runs were performed to verify that the problem was corrected.

The surveillance tests were then performed on 11/22/97 with all results being satisfactory. The EDG was declared operable at 1410 on 11/22/97. The EDG had been inoperable for 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br /> 40 minutes.

l The Lloonses classifies this failed surveillance test as an invalid test and failure per Regulatory Guide 1.108 because the relay is not required to energize in the emergency

. operating mode and because the condition of the contacts would not have prevented ,

Emergency Diesel operation within design limits in an emergency start. The degraded l l relay would have prevented the EDG from operating in the speed droop mode, but l

would not have adversely affected the operation of the EDG in the isochronous mode (emergency mode). Since the "A" diesel generator was, at that time, on an accWorated test frequency of once por 7 days, the test schedule did not change.  !

l Failure of December 2.1997: l On December 2, at 1400, the "A" Fmergency Diesel Generator (EDG) was declared [

inoperable after load oscillations occurred during performance of the surveillance test. -

The test frequency for this diesel had been increased to weeldy from monthly because 7 of the previously described test failures due to problems with load swings.

During this surveillance test, the diesel started normally but, during loading, load ,

oscillations similar to the osciliations observed during the first EGA unit failure (and  ;

less severe that the load oscillations observed during the degraded ID relay ,

troubleshooting effort of 11/21/97) occurred. The diesel was shutdown and CER # 97- i 1362 was written to address the problem.

Act!on was immoc'iately initiated to determine if these_ load swings were due to a- -

defective EGA control unit or due to other defective components providing input to the ,

EGA unit. A troubleshooting plan was developed, instrumentation was installed and i troubleshooting initiated. Additionally, representatives from the governor manufacturer (Woodward) and the diesel manufacturer (Fairbanks Morse Engine Division of Coltec) were called to the site for consultation and independent review of the troubleshooting i effort. Both representatives agreed with the thoroughness of the troubleshooting effort, the conclusions rea:hed and the subsequent repairs. l

_. ,m. _ _ _.-.-___._._.. . . _ _ _ _ . - . _ _ _ _ . . _ _ . , _ _ _ , _

,,,,,_,_.)

. ' Document Control Desk SPR 970002 RC 97 0251 Page 5 of 6 With the EGA uni' encoupled from the mechanical governor (EGB unit), the recorder trace showed spiking from the output of the EGA unit (this spiking was also noted later during a bench test of the failed unit). The EGA unit was replaced with a spare unit from the warehouse. The replacement EGA unit had been previously bench tested in the Electric Shop with satisfactory recults (i.e. no spiking). A maintenance run was performed and the output from the EGA unit was monitored for more that an hour with satisfactory results. Whon the load was removed and the breaker opened, a frequency shift was noted on the recorder trace.

A second troubleshooting plan was generated to adjust the electrical and mechanical governor controls to achieve stable operation. Stable operation could not be achieved.

During the course of troubleshooting, the Speed Raise / Lower Switch on the Main Control Board was found to be sticking. CER 971367 was generated to document and evaluate this condition. The switch was removed, cleaned and reinstalled.

At that time, Plant Management made the decision to replace the newly installed EGA unit from the warehouse with an EGA unit that had been refurbished (on an expedited order) by the governor manufacturer, Woodward Bench testing of this refurbished unit for over a 30 minute period showed no spiking. Several more troubleshooting runs were made to facilitate governor adjustments and additional electrical checks. Once the adjustments were complete, a 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> confidence run was done to gain added assurance of the adequacy ol the repairs and adjustments.

The surveillance tests were then prformed on 12/4/97 with all results being satisfactory. These tests included a normal surveillance test and a load rejection test.

The EDG was declared operable at 0350 on 12/5/97. The EDG had been inoperable for 61 hours7.060185e-4 days <br />0.0169 hours <br />1.008598e-4 weeks <br />2.32105e-5 months <br /> 50 minutes.

The surveillance test was determined to be a valid test and failure per Regulatory Guide 1.108. The test failure rcsulted in 4 failures in the last 20 valid tests and 5 failures in the last 100 valid tests. Since the "A" diesel generator is presently on an accelerated test frequency of once per 7 days, the test schedule does not change.

The two failed EGA units were sont to Woodward for failure analysis and investigation.

Woodward concluded that the first unit failure was caused by a failed amplifier gain potentiometer and the second unit failure was caused by a failed stability potentiometer and a damaged rated speed / idle speed resistor.

Document Control Desk SPR 970002 l RC 97-0251 l Page 6 gf 6 l f

f Should you have any questions, please call Mr. Donald L. Jones at (803) 345 4480. l i

Very truly yot!.w, ,

$ l 0 8,.~e. raast Gary J. Taylor GJT/dij 1

oc.

J. L. Skolds G. A. Robertson W. F. Conway J. B. Knotts, Jr. i R. R. Mahan NSRC  !

R. J. White INPO Records Center NRC Resident inspector RTS (SPR 970002)

L. A. Reyes File (818.08)

A.R. Johnson DMS

- S. F. Fipps i

3 I

i b

r

. _ , , , m. .- -w.,,my, ,y . . , , . - -m--,..-<-

._ , r-.-,e...,. -, ..- e , ,-, , m- --