ML20084U922

Final Deficiency Rept Re Failures of Governor on Emergency Diesel Generator B.Initially Reported on 730504.Vendor Woodward Governor Co Found Malfunction Caused by Grounded Zener Diode

ML20084U922
Person / Time
Site:	Browns Ferry
Issue date:	07/30/1973
From:	Gilleland J TENNESSEE VALLEY AUTHORITY
To:	Kruesi F US ATOMIC ENERGY COMMISSION (AEC)
References
10CFR-050.55E, 10CFR-50.55E, NUDOCS 8306290514
Download: ML20084U922 (4)

Text

O TENNESSEE VALLEY AUTHOAITY O CHATTANOOGA, TENNESSEE 37401 July 30, 1973 amm 0IAYN 0

4,venson, A Ml Mr. F. E. Kruesi, Director Directorate of Regulatory Operations U.S. Atomic Energy Commission Washington, DC 20545

Dear Mr. Krucsi:

On May 4, 1973, TVA made an initial report to AEC-DRO Inspector W. S. Little of the failure of a governor on emergency diesel-generator B of the Browns Ferry Nuclear Plant unit 1. On June 1, 1973, an interim report was filed with your office. In tlw meantime, we made an initial report of another failure of this governor on June 13, 1973. We filed an interim report on July 12, 1973, indicating that we would combine these two failure reports. In accordance with 10 CFR 55(e), we are sub-mitting this final report covering both governor failures.

Very truly yours

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• 6 J. E. Gilleland Assistant to the Manager of Power Enclosure CC (Enclosure):

Mr. Norman C. Moseley, Director Directorate of Regulatory Operations U.S. Atomic Energy Commission Region II - Suite 818 230 Peachtree Street, NW. I Atlanta, Georgia 30303 , ,

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. . . . ENCLOSURE Browns Ferry Nuclear Plc.a Final Report on Foilures of FIBGovernor on Dnergency Diccel-Generator B Model 999-20-645E4 L .

• On February 28, 1973, diesel-generator a was found to be unstable when

. paralleled to the transmission syste:n. The instability decreased cor.ewhat k w'len the load was increased, but the load could not be raised above 1200 lar l wheret.s the continuous rated load is 2600 kw. An investigation uncovered

( a defective Zener diode in the power supply of the EG-A control box (covernor),

and it was replaced. Further testing on March 16, 1973, showed the problem

, persisted. In the process of troubic shooting, the control box was temporarily replaced with the control box from diesel-generator A. Diesel-generator B then performed satisfactorily. The control bo:: for diesel-generator A was replaced and a replacement control box was obtained for diesel-generator B. The B unit was operated satisfactorily with the replacement control box on April 2,1973.

The defective control box was returned to Woodward Governor Company on

, April 21 , 1973, and uoodward was requested to furnish infomation as to 1

the exact nature of the failure. Woodward's report identified the cource of the malfunction as a grounded' Zoner diode. The diode, which had been replaced by TVA, was grounded to the chassis rather then insulated from the

-chassis by sleeves and washers. On'e of the washers was nicked and the-Zener diode was grounded by the mounting scrcv.

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l It is postulated that the original defective Zone; diode una crused by

the sene set of circumstances. This is possible because Woodward's test I I fixture was ungrounded, and therefore, grounded diodes would not be detected except by Woodward's customary checks for grounds with an ohmmeter. However, such checks een casily overlook grounds and Woodward is modifying their i fixture so that it is grounded. This should Icad to discovery of any grounds that could cause erratic behavior and/or discovery of defective components that would develop from such grounds. Although we had not j experienced eny additional similar malfbnetions, we exemined all of the

Woodward EG-A control boxes for grounded Zener diodes and none vero found.

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On June 1,1973, an intomittent condition developed on diesel-generator B.

At first, the governor system failed to respond to remote control cnd then it responded without any corrective action. Irmediately after responding, the signal from the EG-A control box (electronic governor) to the hydrculic

!' actuator was measured and found to be higher than the range specified by the manufacturer. Also, the idling speed was varying over an 80-rpm range.

On June 26, 1973, under the direction of Mr. Edgar Ralls (General Motors Electro-Motive Division field representative), a thorough inspection was 4

made of the diesel-generator B EGBgovernor system. Following the inspection, i

i the hydraulic components were flushed, cicaned, and thc hydraulic oil was replaced. All electrical and mechanical connections in the EC3 governor system were checked. As a result of the inspection, the following abnor-

, malities were discovered:

1. &aall fragments of foreign material were found in the hydraulic actuator oil.

2. Two loose teminals were found on the EG-A control box.

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3. The setscrews on the speed setting adjustment linkage within the EG3 governor actuator were not tightened completely. '

1 The intemittent trouble could not be positively attributed to any single malfunction; however, forcinn material in the governor oil cnd loose ~

g electrical connections are primary causes of sluggish and/or intemittent j Governor control.

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Although the output signal from the EG-A control con exceeded the manu-facturer's specified values, this is an inherent characteristic of the governor system design. Tne specified range of the EG-A control box signals was correct for the interaction of the mechanical-electronic governors on the hydraulic actuator. Tnis signal range is equivalent to the high-to-lov settings of the flyball mechanical governor. The EG-A control box has the capability of providing signals for higher speeds than the mechanical (flyball) governor will pomit. When the nochenical governor reaches its high speed setting, the engine speed vill stabilize even though the electronic governor generates signals .

requesting a greater speed.

The erratic low speed operation was attributed to slippage of nochanical stops on the speed setting ad.justment linkage within the governor actuator.

These mechanical stops were free to move because their setscrews were not properb tightened during assembly or they vibrated loose during operation.

To alleviate such prob 1cas, all terminal connections were tightened, the spcod setting centrol linkage van readjusted, and the mechenical stop setscrcus were tightened foi' diesel-generator D. The governors for the other three diesel-generators were checked for loose terminals on all boards and governors, and the setscrews were also checked for tightness.

The governor oil uns not changed on the three other diccel-generators on the recomnendation of Mr. Ralls because there were no indications of dirty oil. After the checks, all the diesel-generators have been verified to operate properly. In the future, cdditional precautionary measures vill be incorporated in our preventative maintenance program which will include f cleanliness requirements in the handling of governor oil and more frequent chechs of terminal conncctions.

s The safety implication of the diesel-generator problems listed above are l

l identice.l._ Eoth would lead to a reduction in onsite powcr capability; however, the plant could still be shut down using only onsite power with one diesel-generator out of service.

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ENNESSEE VALLEY A HOAITY CHATTANOOGA, TENNESSEE - -

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June 1, 1973 Mr. F. E. Kruesi, Director Directorate of Regulatory Operations Y U.S. Atomic Energy Commission Washington, DC 205h5

Dear Mr. Kruesi:

On May h, 1973, TVA made initial report to AEC-DRO Inspector W. S. Little of the failure of the governor on Browns Ferry Nuclear Plant unit 1 emergency diesel-generator B. In accordance with paragraph 50.55(e) of 10 CFR 50, we submit the following formal report of the failure.

On February 28, 1973, diesel-generator B was found to be unstable

[ vhen paralleled to the system. The instability decreased some-

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j vhat when the load was increased, but the load could not be raised ebove 1200 kW; rated continuous load capacity of the unit is 2600 kW. A defective Zener diode was located in the power supply of

%jf[i the governor and replaced. The unit was run again on March 16, 1973; the problem persisted. The governor was then replaced with Nu\r ' I one from one of the other diesel-generator units. Diesel-generator B then performed satisfactorily. A replacement governor was obtained and installed. The unit operated satisfactorily with the replace-

]s ment governor on April 2,1973. The defective governor was returned to the Woodward Governor Company on April 2h,1973.

The governor is a type EG-A. The engine is a General Motors DID-GM Model 999-20.

Woodward has been requested to furnish information as to the exact nature of the failure. We expect to receive this information -

in time to provide a final report of the incident by July 31, 1973.

Very truly yours, 4 C h 44 ,, _

Godwin Williams, Jr.

Assistant Manager of Power -

CC: Mr. Norman C. Moseley, Director O

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Directorate of Regulatory Operations U.S. Atomic Energy Commission

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230 Peachtree Street, NW.

Atlanta, Georgia 30303 3 0416

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0 0 Tennessee Valley Authority Docket No. 50-259 ATTN: N . Janes E. Uatson Manar,cr of Power 818 Power Building Chattanooga, Teunessee 37401 Centleten:

Thank you for your Ictters dated July 6, 1973 and July 9, 1973, which forwarded reporta pursuant to 10 CFR 50.55(c) regarding the failure of two flow switches, and the failure of y uplincs in the RP.R Service Water Systcu and a raiket in the Energency Equiptent Cooling Uater Syntcu at the Browns Ferr*f :,uclear Plant '

Unit 1. Your reports will be reviewed and evaluated and, ehould vc require additional information concerning this tatter, we vill contact you.

Your cooperatica concerning this catter in appreciated.

Sincerely, Criginst , 4 ,by O Tksenc g f/

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J. G. Davis, Deputy Director for Field Operations Directorate of Regulatory Operarions bcc with copy of letters dtd July 6 and July 9.

N. C. Moseley, RO:II, w/o encl.

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