ML18153A606

LER 90-004-00:on 900522,reactor Trip/Turbine Trip Occurred. Caused by Inadvertent Actuation on a Main Transformer. C/A:Main Transformer Was inspected.W/900621 Ltr

ML18153A606
Person / Time
Site:	Surry
Issue date:	06/21/1990
From:	Kansler M VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
90-377, LER-90-004-03, LER-90-4-3, NUDOCS 9604240012
Download: ML18153A606 (9)

Text

... ' *., MAR 05 '96 10:08 NLD e P.2/10 VIRGJNIA ELECTRIC ANO POWER COMPANY .

Suny Power Statum P.O. Box 31S Suny. Virginia 23883 U.S. Nuclear Regulatory Commission Serial No.: 90-377 Document Con~ol Desk Docket Ho. : 50-280 Washington, O.. C. 20555 50-281 License Ho. : DPl.-32 DPR-37 Gentlemen:

Pursuant to Surry Power Scacion Technical Speci.f1carious. Virginia Elec~ric alUi Power Company hereby submits the follOlriug Licensee Event Repo~t far Unies land 2.

REPORT NUMBER 90-004-00

'Ibis r11::yort has beeu reviewed by the Stat:Lcn Nuclear Safety and Operating I Committee and w:il1 be reviewed by Corporate N11clear Safety.

Very truly yours,

.).

~~6-(!.J1.. Kansler Station Managet:

Enclosure RECEiVED BY cc: R.egioual Admiuistrator Suite 2900 101 Mariet-ca Street, NW NOV 1 6 1990 Atlanta, Georg~a 30323

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'I I On May 22, 1990 at 1150 hcurs with Units 1 and 2 at 100% power, a fa.ult occurred on the Unit l "A" main cransformel:" as a result.of an ina.dverten~ actuation of the transfarme.r's deluge system. the fault II I-initiated a Unit 1 generator differential lockout which immediately initiated a turbine trip/re!!actor trip. The fault also resulted in the lockout of the "A11 ReserV'e Station Service Trausfomer (:RSST).

Approximately 10 seconds later, the Unit 2 control room operator initiated a mauual reactor trip after observing erratic control rod I Individual Rod Position Indications (IRPI). Opera~o~s performed the appropriate plant pr~cedures and quickly stabilized the units following the trips. The erratic- Unit 2 IRPI indtcations were due to voltage transients that occurred on both units' etiie~gen~y b~~e$

which were caused by the Cnit 1 generator tl:'ip, the 11 A11 RS$T lockout, and subsequent motor star~s. The #3 Eme~gency ntesel Generator automatically restored power to the Uni.t;: 1. "J" eme-rgency bus which was de-energized by the "A 11 RSST loc:kou1;. A four hour non~ergency report waa made to the Nuclear Regu.Latory Commission in accordance with 10CFR50.72.

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• 1A1i1 .'.'

• LICENSEE EVENT REPORT (LERI TEXT CONTINUATION

.UA6v&& 6i.ta N6. 3,so-0106

!XPIIIIGS: ":Klllrl UTIMATIO IUAOEN llliFI Rll5PONSi. TO CQ,Wll,V WTW TMIS INIIORMUION COLLECTION Ri0UE$T: 50.0 IIRS. FORWARD C:OM"'laNTS Rl!G .. AOINCi IIUROEN laSTIMATE TO TH! Al;CORDS AND Rl!POIIT5 MANAG~1"iiNT IRANCH IP,5301. U.S. NUCL~R Rl!GULATOIIV COMMISSlO."I, Yt"'$HINGTQN. 0C :OS6S, ANO TO l"HE PAPi!!RwORt.-: 51EOUCTION i'ROJ!cT Clt!Q.(11041. oi;i;1~

01' MANAGEUENT ANO 8U0Cl;T. WASHINGTON. 0C~ll$0l.

I DOCKET NUMe!R J21 ~ill NUMUR COl PAGI Cll I

Su b:'y Power Station, i.:nits l and 2 o Is I o 1o ; o I 2 l 8 I o 9 Io 1- o I o14 . J- OIO 012 OF OJ6 l.O Descrintion of the Event On May 22, 1990 at 1150 hours0.0133 days <br />0.319 hours <br />0.0019 weeks <br />4.37575e-4 months <br /> with Units l and 2 at 100% power, a fault occurred on the Unit l "A" main transformer as a result of an inadvertent actuation of the transformer's deluge system. The fault initiated a Unit l generator (EIIS-GE~,TH) differential lockout which immediately initiated a turbine trip/reactor trip. Approximately 10 seconds later, the Unit 2 control room operator initiated a manual reactor trip after observing erratic control rod Individual Rod Position Indications (!RP!) (E!!S-2I.AA).

Approximately two minutes prior to the tripst control room annunciators alerted conerol room operato~s of the actuation of the 11 A" main transformer deluge system (EI!S-KP). Plant operators were dispatched to the transfor.ner and verified that no fire existed and initiated isolation of the deluge syste~. As plant operators we~e isolating' the deluge, arcing was observed from the "A11 main transformer to the generator output isophase bus duct and t:o the "An Reserve Station Service Transformer (RSST) (EI!S-XFMR) bus bars. In addition to the generator differential lockout, the arcing initiated a. lockout of the "A" RSST, which coupled with the Uuit l gene~ator trip, resulted in de-energizing the Unit l "A" Station Service (SS) (EIIS-'EA) bus and the Unit l "J" 4160V emergency bus (EIIS-EK). The #3 Emergency Diesel Generator (EDG) (E!IS-GEN,EK) automa.t~cally started and restored power to the t1n1t l "J" bus within seconds of the "A" RSST lockout. Majo-r equipment supplied by the Unit l "A" SS bus includes the "A" Reactcr Coolant Pump (EIIS-P,AB), the "A" Main Feedwater Pump (EIIS-P, SJ) and the "A Condensate Pump (EIIS-P-KD). The "C" condensate pump automatically started when the "An condensate pump was de-energiz:;ed..

Following the iuitiation of the manual Un.:L.t 2 reactor trip, a Uuit 2 generator trip occurred as desigued 24 seconds later. The 11 A" RSST a.lsc supplies the Unit 2 "A" SS bus when the unit generator is off line.

Consequently. the lockout of the "A" RSST. c:ou.-pled

.t NRC F!)R . 3&MAR 05 '96 10: 09 NLD e

U.S. NUCl.fAA ltl!GULA TORY CQMllffllSlQH

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e LICENSEE EVENT REPORT ILER> l!STIUATGO 81.lROl!N PER REPONSf: TO COMPLY WTM TMIS INFORM.t.TION COLLliCTICN Af:QuiST: !50.0 HR$. FORWARO CCMM!iNTS REGARDINO BURDf.N iSTIMATE TO TH~ AEc0t'1D:i TEXT CONTINUATION ANO A1590RTS IIIANAGEMeNT IIRAfllCN 11*-SJOI. U,S. NUCl.l!AA REGULATO>IY cor,U,'IISSICN. WA5MIN<;iTON, DC =!!. ANCI TO n1e PAl'l;RWORIC lleOUCTION PROJl;CT (3150-0111'1. o,,,ci OF MANAQliMeNT ANO BUDGET, WA$i'IINGTON, DC 20=o:J.

ICOCKl;T NUllllilR IZI Lll!II NUMllll!lt 1111 PAGI 131

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Su; y Power Station, U:1its l and 2

,e,.,..1 1n lo ls f o l o Io I 2 rs I o 9 I o - Of OJ4 - o I o 01 3 OF 016 with the Unit 2 generator trip, resulted in de-energizing the Unit 2 11 A11 SS bus. Major equipment supplied f-rom this bus, including the Unit 2 "A" Reactor Coolant Pump and Unit 2 "A" Main Feedwater Pump; was de-energized. A load shedding scheme designed to shed various loads from both Units' SS buses to maintain voltage on the RSS buses was initiated. This resulted in tripping the second Unit 1 Main Feedwater Pump terminating Unit l tnain feedwater flow. How~ver. the auxiliary feed pumps had started as designed on lo~ Steam Generator (S/G) levels prior to the tripping of the second main feedwater pump and provided sufficient feedwater to the steam generators to recover level.

Following the trip, safety systems on both units functioned as designed, and beth units were stabilized. A four hour non-emergency report was made co the Nuclear ReiUlatcry Cotmnission in accordance

~ith 10CFRS0.72.

4 .0 Safetv Conseauences and !mglications During the event, the turbin~ protection and reactor protection systems for both units functioned as designed. The #3 Emergency Diesel Generator automacica.lly scarted and loaded onto the Unit 1 11 J 11 E'.mergency Bus as designed to restore power to the bus.

The loss of all Main Feed~ater ou Unit l was not significant as the Auxiliary Feedwater Pumps started and provided adequate feed~ater flow to the steam generators co maintain a heat sink for the reactor.

The two remaining Reactor Coolant Pumps en each unit continued to operate to provide forced flow through the reactor and maintain the reactor in a hot shutdown condition. There are no safety consequences associated f.l'ith the de-energization of each units' "A 11 Station Service Bus since equipmenc powered from ehese buses are not required to ensure safe reactor shutdown

_ or to mitiiate the cousequences of an accideuc.

Therefore, the health and safety of the public were not affected.

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i-c, Ol~----- u,11ovEo OMii ~-3150-0104 EXl'IAH: 4/lo/ln 6/J.

l E$TIMATEg IILll'IOl;N ~!ail lli;SPCNU TO C()Ml'~V WTIOI nus LICENSEE EVENT REPORT (LER) il\lFQRll,l,4.TION COLLl;CTION AE(ll.J!Si': SO.O HAS. FOl'IWAAO

,;QMl,li;NTS REOAACIING 8UR01;1\1 ESTlll,IATli TC TWE RECORCS TEXT CONTINUATION 41110 FIEPORT$ MANAGSMi;NT BRANCH IP*SlQl, U.$. t.uet.l!AR Ri<iULATOAY COMMISSION. Wl'-SHINGTON, OC mM. ANO TO THli IIAi>iRWOfh( REOUCTION PAOJEl;'r (J150<)I04J. 0/IFIC! r OF MANAGl!M!NT .a.NO BUDGET, W*>>tll\lGTON. OC: 2~03. f FA::11.:

$1 NAMI !11 ry ?ower Station, ~nits 1 and Z Ooet(i.T Nu~e111 1:z1 L~R NUMc1u1 101

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!he arcing which occurred on the Unit l main tranafc?:1ner has been attributed to the actuation of the 11 A" main deluge system which contained corrosion product contaminants. The distance between the "A" RSST bus bars a.nd the 11 A" Main Transformer 230KV leads is in confonnance with electrical codes and standards.

However, the proximity of these conductors is believed to have been a contributing factcr to the loss of the 11 11 A RSST.

Approximately 20 to 30 minutes prior* to the actuat.ion of the transformer deluge system, a construction employee inadvertently bumped the weather enclosure cabinet for the Unit 1 transformers' deluge manual pull stations. The employee verified the pull staeion had not actuated immediately after he bumped the cabinet. However, following the event, the manual pull station was discovered in the actuated position.

The pull stations are maintained in the de-actuated positicn by a glass rod which holds the pull lever in the upright position. The pull station is actuated by pulling down the lever which breaks the glass. The pull station will also fail to the actuated position if the glass fails. It 1s surmised that the glass failedt and the pull station actuated 20 to 30 minutes after the enclosure was bumped~

The Unit 2 !RPis are powered from the Unit 2 semi-vital bus, which in turn was po~ered from the Unit 2 11 J 11 emergency bus. The transformer that supplies power to the IRP!s 1s designed to maintain its output voltage with+ 0.5% when the input voltage is within+ 10%. Following the Unit l t~1p, a. voltage.

transient ;cc:urred on both units emergency buses. due to the fault and subsequent large motor starts. The voltage transient on the Unit 2 tt.rn eiuergency bus exceeded the + 10%. This was sufficient to cause significant fluctuations in the IRPis which prompted the Unit 2 operator to trip ehe Unit 2 rea~tor. (Refer

- to Attachment l for break.er pos*it1ons.)

4.0 !mmediate Corrective Action(s)

Operators followed appropriate plant procedures to quickly stabilize the units following the respective reactor trips. Also, the Shift Technical Advisor L..--1~------------------------**-----*-

NRC IIOl'I

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~MAR 05 '96 10: 10 NLD A u.s. NUCUAR REQULATCRV C:OMWIU"'N LICENSEE EVENT REPORT (LER)

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Su. y Power Station, Units land 2 o Is ! o I o ! o I 21 s 10 9 Io 1- o I 01 41- oIo oIs oi:

monitored the critical safety function status trees to ensure specific plant parameters were noted and that those parameeers remained within safe bounds.

5.0 Additional Corrective Action(s)

All main and station service transformer deluge systems were flowed in accordance with periodic test procedures.

The fire protection manual pull stations for the Unit land Unit 2 transicrtllers have been replaced with pull stations which are less susceptible to inadvertent actuation.

The "A" Ma.in 'transformer was inspected following the trip and no preexisting conditions which could have caused the arcing were found.

The High Voltage bushing en the output on the Unit l 11 A" Main transformer, whic.~ was damaged. by the arcing, has been replaced.

A lightning arrestor on the "A" RSST damaged by the arcing has been r~placed. In additiont slight damage to the 4160V bus bars from the 11 A" RSST was repaired.

6.0 Action(s) Taken to Prevent Recurrence tn addition ca the corrective actious described above.

evaluacicns of enhancemencs to the IRP! system and ita power supply are being conducted. An evaluation will be pe~fo~ed to determine the feasibility of enhancing the separation bet.ween the "A" Main Transformer* a.nd the "A" Reserve Station Service bus bars. In the interim, the deluge system to the "A" Main Transformer has been isolated based on engineering g,~idance, and an evaluation of t~e deluge system is being conducted.

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1'"'~.8/1~~--------_,,.

e LICEN$EE EVENT REPORT ILEA)

IJ.$, JfUC:UAR IUiGIII.A TOIIV COMMISSION * >>~Yl!D o,,,1 ..o. 3150 ,0,04 eXPIAEiS: 4 ~

QT1MATEO IIURCIEN Pill! RliSIIOHII! TO CQl,Ull,V WTM Tl,f1S IN¢0Ri..it.TION COLLECTION FIEOIJ!S'f: ~O.CI MAS. ,ORWARO CQIIIIMli ..TS fll!GAAOING UURt'EN li5TIMATE TO THE Rl!CORC5

'v TEXT CONTINUATION ANO AU¢R1S P,,tANAGEMlil\lT ~ANCM iP*9JOI, U.S. NUCUAR REGU!.Al'O>!V COMMISSION. WA/;>UNGTON. CC 20555. ANO TO 1'ME PA,.l;RWORK RECUCTION PAOJl!CT c:111i0-01041. CFFICI 01' MA~EMiNT I.NO 8UQGET. WASHIH<iTOH, CC 20803.

FAC!&:.IT NAMII (1 I DOCICliT IIWMllill 121 1.!fl JfUMHII Ill I

S~ ~Y Po~er Station, Units land 2 o 1s Io Io Io I 218 I o 910 - o f Oj 4 -, o 10 0 J6 0~ OJ 6 T&xT Ill. ~-

• IW'//llff, 11* .ulfiDMi /liRC Fann J!illA -., ill) 7.0 Similar Events LER 1*89-44: "Manual Reactor 1'rip/Turb1ne Trip Initiated Following Less of Power to Semi-Vital Bus c:au1:1ed by a Fa.ult on 11 A" RSST". This event: occurred due to roofing material blowing off the turbine building roof and faulting the "A" RSST.

a.o Manufacturer/Model Number(s)

General Electric Single Phase, 60 cycle 1 Class FOA (Manual GEK*l64l2).

Moloney LTC (Load Tap Changer) Transformer, Type MA, Design X-760.

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P.10/10 MAR 05 '96 10:12 NLD e

Breaker Position After Event Ul and U2 Generator Output Breakers Open LER 280...90-004 Attachment 1 From offsite distribution Fram oifsite distribution Figure 2 34.SKV 111ill(

4160V 4160V 1SH8 Emerg.6us Emerg. Bus 1H 2H

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