ML20028H863

LER 90-023-00:on 901230,generator Neutral Ground Overcurrent Protective Relay Actuated & Tripped Main Generator.Caused by Internal Generator Defect.Main Generator Disassembled & Rotor Removed to Locate ground.W/910124 Ltr

ML20028H863
Person / Time
Site:	Braidwood
Issue date:	01/24/1991
From:	Kofron K, David Nelson COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BW-91-0083, BW-91-83, LER-90-023-02, LER-90-23-2, NUDOCS 9101310179
Download: ML20028H863 (5)

Text

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4' O Braidwood Nuclear Power Station v* Route #1, Box 84 Bracovillo, Illinois 60407 A Telephor se 815/458-2801 January 29,1991 BW/91-0083 U. S. Nuclear Regulatory Commission Document Control Desk

. Washington, D.C. 20555 j

Dear Sir:

The enclosed Licensee Event Report from Braidwood Generating Station is being transmitted to you in-accordance with the requirements of 10CFR50,73(aX2Xiv) which require a 30 day written report.

This report is number 90-023-00; Docket No. 50 456.

Very truly yours,

, "Y.

w K. L. Ko ron Station Manager Braidwood Nuclear Station KLK/DN/cif-(226/ZD85G)

Enclosure:

' Licensee Event Report No. 90 023-00 cc: NRC Region III Administrator

-NRC Resident Inspector INPO Record Center CECO Distribution List -

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9101310179 910124 +

PDR .ADOCK 05000456 S PDR

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ll LICENSEE [ YEN? REPORT (LER) g Facility Name (1) Docket Number (2) Paos (3)

JI11)Lwgod Linit 1 01 $I 01 01 01-41 51 6 l'!ef!0l4 Title (4)

Reactor Trip Caused By Main Generator Phase C Grouno Fault Event Daltj$)' LER Number (6) Reogr.Lpt(e (7) 01htL[Atilities Involved _.(8)

Month Day Year. . Year f,/,

// Sequential // Revision Month Day- Year Facility Namti_ JQd.ti.Rdith)

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_1LLall Jtl_D.. 910. Of_2 13 0I p.__ 01 i 21 4 _91 i_ c1_11213101 I l OPERATING

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MODE-(9) 1 _ 20.402(b) __ 20.405(c) _)L 50.73(a)(2)(iv) _ 73.71(b)

POWER _ 20.405(a)(1)(t) ._ 50.36(c)(1) _ 50.73(a)(2)(v) __ 73.71(c)

LEVEL 20.405(a)(1)(ii) 50.35(c)(2) 50.73(a)(2)(vii) Other (Specify 0l9l

_111) 8 _, 20.40$(a)(1)(iii) __ 50.73(a)(2)(1) __ 50.73(a)(2)!viii)(A) in Abstract

/////////////////////////,/ _ _. 20.405(e)(1)(iv) __ 50.73(a)(2)(ii) _ 50.73(a)(2)(viii)(B) below and in 20.405(a)(1)(v) 50.73(a)(2)(n) Test)

////////////////////////}//

_.,50.73(a)(2)(iii) _

Li([H$ Ell 0NTACT FQRJ1SlLR (12)

Hame. TELEPHONE NUMBER AREA CODE

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CAUSE $YSTEM COMPONENT KANUFAC- REPORTABLE CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE TURER TO NpRDS TUR(R TO NDRDL i x I LIL_ 31EINl* . WI 11211 YE5 I I l 1 _L.1 I I I I I i 1I I I I I I I I

_$VEELEMENT At REEQPT EXPECTED (14) Expected tionth l Day l Ygg Subelssion

" ll l Y t13.l_l,.2f b_iQmp1 tit 1Ef'(ClEQ_SUILM11$1DN D A T E ) 5lNQ_ l _[_

AB$TR M T (Limit to 1400 spaces,--l.e, approximately fifteen single-space typewritten lines) (16)

On December 30,1940, Unit 1 was load following to accomodate system demand for the Comonwealth Edison Company system load dispatcher. At 0815 the Unit completed a power ascension to full capability. At 0821 a Gonerator Neutral Ground Overcurrent protective relay actuated and tripped the Unit 1 Main Generator. A turbine andLreactor trip followed as designed. Megger testing revealed a ground on the "C" phase of the Mair

-Generator. The cause of the ground was an internal generator-defect. The generator vendor. Westinghouse, was contacted to provide assistance in locating the f ault. Upon application of Hi potential Alternating Current to the "C" Phase, observation of smoke and electrical arcing revealed that the fault was in the bottom coll'in~ slot 29 of the stator. Damage to the coil was attributed to a vent spacer that came loose.

Vibration during normal operation allowed the.sracer to rub and wear down insulation protecting the coll.

The ground-was created as a result of insulation breakdown. The coil was-removed from the stator and sent to the: vendor. This component failure is considered to be an isolated event. There have been previous occurrences of a reactor trip caused by a generator trip. previous corrective actions and contributing root cause are not applicable to this event.

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3102m(012591)/1 l 4

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. i LittWlt EYtWI kt>0RT f LER) IIIT CONF fit &Q1eN Fa m tev 1.0 f Atitif f NAME (1) DOCKtf M)ett (2) _ 1LL N#9tR f61 Pane (31 Year /// Sequentiel fff //j ff

/ Revisien I11 Nabe r LL.L2de

,tawnLt o_1 5 i e i e i e I di 51 6 91 0 - el213 . e1 o el 2 er el 4 lisl trergy Industry Identification Systee (t!!$) codes are identified in the test as (U)

A[ Flant Conditions prior to twent:

Unit: Braid ood 1; twent Date: December 30, 1990: Event time: 082):

Mode: 1 tower Operation: R Power: 0987:

RC$ (AB) Temperature / Fressure: NOT / HOF; C. Description of Event:

There were ne systees or components inoperable at the beginning of the event which contributed to the severit.y of the event.

On December 30,1990, Unit 1 =as load f ello ing to accomodate systee demand f or the Comen ealth Edison Comc any syste- load dispatche- At Obit the Unit comrittet e re=er ascension to full capability. At 0921 a Generator Neutral Ground Overeverent protective relay actuated and tripped the Unit 1 Main Generator (TG)

[TP). A turtsine and reac ter trip followed as designed. All contre) rods f ully inserted and due to the turtine trip at high re-er, stes* genevator (HD (SB) levels shrunn to the lo.le level setpoint. Both Auxiliary feed.ater (Af) (BA) puers auto-started as designed to restore steam generator level.

On-site power supply disturbances, caused by the Main Generator Trip, were sensed by Area Radiation (AR) (IL) monitors loc ated inside Containment and the Fuel Handling Building. The monitors in (ontainment generated a Containment Ventilation (VQ) (VA) Isolation Actuation Signal. No cceponents repositioned as all were in their. required ($ elation position, the fuel Handling Building radiation monitor initiated an automatic start of the fuel Handling Building Charcoal Bocster fan (VA) (VG). These monitors responded as designed on a d comentary less of power, l l

All ether systees functioned as designed. Operators perf orined apriicable steps of the reactor trip response procedures to stabilire the plant. Availiary f eed.ater was secured af ter stese generator levels were

<- restored to their normal operating level. Upor verification that high radiation levels did not exist. the

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Containment Ventilation Isolation Actuation Signal was reset, and the f uel Handling Building Ventilation was

-restered to a norwat lineue, The appropriate NRC notificatter via the [N$ phone syster .as made at 0955 pursuant _ to 10Cf R50,72(b)(2)(ii),

leitiP11), there was difficvity iselating the Maie Power (Hr! (LL) 1ransf eriners (Mri) because the Main Generator disconnect lin6 age had freren. Outside air temocrature hae dropped belo.10 degrees I af ter a rainsterir on the trevious day. It's situatior was corrected and the Mri's were isolated,

, at 100(i stable plant tenditions -e e acheived and operators erited the Braidwood Emergency Procedure (B tp)

(5-0.1, Eeactor 1 rip Sesponse, and enterec Braiewood General Procedure (BwGP) 100-5, Plant Shutdown and Cooldown, this event is being recorted pursuant to 10CrR$0.73(a)(2)(iv) - any event or condition that resulted in manual or automatic attuation of any Engineered Safety Feature, including the Reactor Protection System.

.3102m(012591)/2

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I LEIM)EE EVENT REPORV f LERI VEXT EQHIIM110N Fern try 2 J ,

FAClllTY NAME (1) DOCKET R M ER (2) LER W M ER f61 Pane (31 ,

Year // Sequential // Revision l

• /j/jj 14 bsbar . /j/j

/j/_ Number l

_Dnidwned 1 o13IoIcLQl41516 9Io - o1213 - oI o el 3 or el 4

'VEXT Energy Industry Identification System (E!!S) codes are identified in the text as (XX) l C, Cause of Event:

i l l- Inspection of Generator protection relays identified that the ground overturrent relays had tripped on the l MPT's. The Generator disconnect links were removed to allow testing / troubleshooting of the Main Generator separate from the transformers. Testing of the transformers indicated that they had functioned correctly, i Megger testing revealed a ground on the "C" phase of the Main Generator. The cause of the ground was an internal generator defect. The generator vendor, Westinghouse, was contacted to provide assistance in locating the fault.

The cause of the Containment Ventilation Isolation Actuation $lgnal was a momentary loss of power to the containment fuel handling incident radiation monitors. )

i The auto start of the Fuel Handling Building Charcoal Booster f an was a momentary loss of power to the fuel hondling building incident radiation monitors.

D. Safoty Analysis:

Plant and public safety were not affected. The generator neutral ground overcurrent relay isolated the generator from the system grid. Redundant trains of reactor protection (RP) (JG) and engineered safety footures (Ef) (JE) were operable, available and effective in performing their design functions.

Under the worst case condition, if a generator f ault caused a total loss of of f site power, emergency diesel ,

generators (OG) (EK) would supply the Er elecrical power requirements. This event is analyzed in Section 8 i

, .of the Updated Final Safety Analysis Report, ,

l 4 E. Corrective Actions:

The Main Generator was disassembled and the rotor was removed to locate the ground. Upon application of Hi i potential Alternating Current to the "C" Phase, observation of smoke and electri:al arcing revealed that the fault was in the bottom coil in slot 29 of the stator. Damage to the cell was attributed to a vent spacer that came loose. Vibratie- ring normal operation allowed the spacer to rub and wear down insulation protecting the coll. The . >und was created as a result of insulation breakdown. The coil was removed from the stator and sent to the vendor. This component failure is considered to be an isolated event.

After replacement of the defective coil, the generator will be reassembled. The Unit is scheduled to return

to service in late February 1991.

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LLC [Ni[L{ VENT REPO(( (LER) T[ri CONI [M.nllQN form RPv 2.0.

FAC]LifY NANC (1) DO:K(1 NVHDCR (2) _L(pJ)T[Lif) F09t_131 year Sequential Revision fff UL -tlumktr fff llL - B a ktt-

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Jnidned 1 015 1 0 1 0 IJ_llL5L1_LLt - 01213 -

-J0 0 01 4 or ;La ilti Energy Industry identification Syster ([115) codes are identified in the text as (X1]

f. Previous Octurrences:

Thes e have been pre = tous occurrences of a reactor trip caused by a generator trip. Frevious corrective actions and contributing root cause are not applicable to this event.

G. Component f ailure Data:

Manufacturer Nomenclature Model Number mfg Part Number

' Westinghouse Generator 83r72) 1313r19 Stator Coil J

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