ML19327B477

LER 89-029-00:on 890922,ESF Actuation Occurred When Diesel Generator 1A Started Due to Momentary Undervoltage Condition on Train a 4,160-volt Essential Switchgear.Cause Unknown. Offsite Power Source Returned to Normal svc.W/891023 Ltr

ML19327B477
Person / Time
Site:	McGuire
Issue date:	10/23/1989
From:	Mcconnell T, Sipe A DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-029, LER-89-29, NUDOCS 8910310255
Download: ML19327B477 (6)

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Ol . Duk hauer Ouyany (704)Sf5 4MO i

' McGuirr Nuclear Station fu liar 458 '

Corachus, NC 280310488

, DUKEPOWER October 23, 1989 )

U.S. Nuclear Regulatory Commission Document Control Desk )

Washington, D.C. 20555

Subject:

McGuire Nuclear Station Unit 1 }

Docket No. 50-369 Licensee Event Report 369/89-29 Gentlemen Pursuant to 10 CFR 50.73 Sections (a)(1) and (d), attached is Licensee Event

. Report 369/89-29 concerning the Unit 1 Diesel Generator'A automatically starting because of an undervoltage condition. This report is being submitted in l accordance'with 10 CFR 50.73(a)(2)(iv). This event is considered to be of no  !

significance with respect to the health and safety of the public.

Very truly yours, ,

s lo *< < /71.*

T.L. McConnell DVE/ADJ/cbl ,

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Attachment  ;

xc: Mr. S.D. Ebneter American Nuclear Insurers j Administrator, Region II c/o Dottie Sherman, ANI Library  :

U.S. Nuclear Regulatory Commission The Exchange, Suit 245 .

Is 101 Marietta St., NW, Suite 2900 270 Farmington Avenue  !

Atlanta, GA 30323 Farmington, CT 06032 i l INPO Records Center Mr. Darl Hood '

Suite 1500 U.S. Nuclear Regulatory Commission 1100 Circle 75 Parkway Office of Nuclear Reactor Regulation  :

Atlanta, GA 30339 Washington, D.C. 20555 t

t L M&M Nuclear Consultants Mr. P.K. Van Doorn L 1221 Avenue of the Americas NRC Resident Inspector }

l New York, NY 10020 McGuire Nuclear Station l

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., v bac B.W.,Bline j .A.S. Daughtridge R.C. Futrell R.L. Gill-

.R.H. Glover (CNS) ,

T.D. Curtis (ONS) ,

P.R. Herran 4

S.S. Kilborn ()!)

S.E. LeRoy R.E. Lopez-Ibanez

. J.J. Haber R.O. Sharpe (MNS) ,

G.B. Swindlehurst K.D. Thomas L.E. Weaver [

R.L. Weber  !

J.D. Wylie (PSD) l J.W. killis QA Tech. Services NRC Coordinator (EC 12/55)

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l , l On September 22, 1989, Unit I was in Mode 1, power Operation, at 83 percent power. .

Hurricane Hugo was causing high winds and rain at this time. An Engineered Safeguards Feature (EST) actuation occurred when Diesel Generator (D/G) 1A started due to a momentary undervoltage (UV) condition on the Train A 4160 volt Essential  ;

Switchgear (ETA) caused by the Train A offsite power source (BLIA) de-energizing to isolate an apparent directional ground fault. The 6900 volt switchgear automatically transferred to its standby source, Train B, (BLIB) as designed, thus 3 supplying power to ETA. This prevented the D/G breaker from closing by clearing the undervoltage condition. The Turbine ranback to approximately 46 percent power ,

when BLIA was de-energized. This event is assigned a cause of Unknown Cause because the exact cause of the ground could not be determined. The high winds from the hurricane were probably responsible for the grounds. Operations (OPS) j personnel verified proper plant response to the runback and secured D/G 1A. BL1A was restored to normal service and the 6900 volt switchgear was realigned to its normal power source.

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EVALUATION: I

Background

f Each unit at McGuire Nuclear Station has two independent Diesel Generators (D/Gs) '

[EIIS:DG). As part of the Essential Power System [EIIS:EK], they provide standby i' AC power to the equipment required to safely shutdown the Reactors [EIIS:RCT) in the event of a major accident and to maintain the facility in the shutdown or l refueling condition for extended periods of time. The D/Gs are required in a Blackout (loss of normal powet) condition as well as a Blackout and Loss of Coolant Accident condition.

Technical Specification (TS) 3.8.1.1 requires:

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a. Two physically independent circuits between the offsite transmission network and the Onsite Essential Auxiliary Power system, and  !

b. two separate and independent D/Gs.  :

These are required in Mode 1 (Power Operation), Mode 2 (Startup), Mode 3 (Hot Standby), and Mode 4 (Hot Shutdown).

Protective Relays [EIIS:EA) are provided to isolate components in the Onsite Power System or the Offsite Power System from any condition that may prove detrimental to the effective operation of the component. This can include isolating part of the '

Onsite Power System from the Offsite Power System if the fault condition is ,

detected in the Offsite Power System. This relaying in divided into zones. Zone 1A includes Power Circuit Breakers (PCB) [EIIS:52) 8 and 9 located at the McGuire switchyard [EIIS:FK] and Generator Breaker 1A and the Train A 6900 volt switchgcar breakers located at the McGuire site. A phase fault or a ground fault detected in '

this zone will open all of these breakers. An auto transfer feature is included in i provide power to the Train A 6900 volt switchgear from the redundant offsite  !

. source.

5 UV relays monitor the 4160 volt Essential switchgear. If 2 out of 3 of these ,

relays detect a UV condition, a signal will be sent to start the associated D/G.

If the UV condition is still present after a predetermined time, the D/G will  :

assume the electrical loads of the switchgear.

Description of Event On September 22, 1989, Unit I was operating at 83 percent power. The unit was at e

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reduced load because of reduced system demand. The dispatcher had requested the , ,

load reduction. Hurricane Hugo was passing through the McGuire area with wind gusts in excess of 60 miles per hour.

At 0621, a BLIA Transfer Trip Lockout occurred when Protective Relays 67GT, Directional Ground, actuated. These relays have four sensors which monitor for relatively low current (400 amp) grounds that remain for a certain time delay.

When 2 of the 4 sensors detected the ground long enough, PCBs 8 and 9 tripped.

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0l 0 0l3 of 0 l4 rent e --. . =ac w an w nn This separated BLIA from the McGuire switchyard. The BLIA Transfer Trip Lockout sent another trip signal to PCBs 8 and 9 tripped Main Generator Breaker IA and its associated Motor Operated Disconnects (MODS) (EIIS: MOD), and tripped the 6900 volt switchgear breakers fed from BLIA. This cleared Zone IA. When the 6900 volt breakers tripped, the standby breakers fed from Bus Line IB automatically closed to  ;

supply power to the Train A 6900 volt switchgear and to the components it normally feeds. This includes Train A 4160 volt essential switchgear (ETA).

During this time, ETA had a momentary W condition as sensed by 2 of 3 W relays.  ;

These relays started D/G 1A which was at full speed at 0622. By this time, the '

6900 volt switchgear had transferred to their standby source and the W condition had cleared on ETA. This prevented the D/0 1A Breaker from closing but the D/G continued to run.

During this same time, the Main Generator was automatically reducing load to 46 percent power. This was caused by loss of BLIA. The runback functioned as designed and the OPS personnel verified the plant was stabilizing. OPS personnel ,

secured D/G 1A at 0639.

At 0715, the NRC was notified of the. ESF actuation as required by RP/0/A/5700/10, NRC Immediate Notification Requirements. Also at 0715, OPS personnel verified that  ;

the Train B offsite power supply was available as directed by TS 3.8.1.1. OPS personnel also reset the Transfer Trip Lockout after discussions with the dispatcher and inspecting BLIA for problems. No problems were found. The dispatcher requested OPS to restore BLIA and increase load as soon as possible.

At 0718, PCB 8 was teclosed snd at 0720, PCB 9 was reelosed. This restored power from the McGuire switchyard to BLIA. At 0800, the Generator MODS were closed; ,

Generator Breaker IA was closed; and the 6900 volt switchgear was realigned with their normal breakers closed and their standby breakers open.

Conclusion This event is assigned a cause of Other/ Unknown because of possible external causes. The exact cause ot' the 67GT relays actuating could not be determined.

These relays caused BLIA to be de-energized thus creating a momentary W condition on ETA This W caused D/G 1A to be started. Station personnel believe that the high winds and extreme weather conditions created by Hurricane Hugo were related to this event. The area surrounding McGuire sustained much damage including many trees being blown over. There was a large amount of debris being blown about.

Some of this debris could have blown into the power lines.

A review of McGuire Licensee Event Reports (LERs) for the previous twelve months revealed three events involving Other/ Unknown causes with ESF actuations. LER 369/89-04 involved Unit 1 Steam Generator Tube Rupture. LER 370/8,9-01 involved a Unit 2 Reactor Trip when Control Rods dropped during a Pod Movement Test. LER 370/89-02 involved a Unit 2 Reactor Trip due to switen f,illures and a broken air line. None of these events particulars were similar or involved possible internal causes. This event is not considered recurring.

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i This everst is not Nuclear Plant Reliability Data System (NPRDS) Reportable, r

There were no personnel injuries, radiation overexposures, or releases of I l, .

radioactive material as a result of this event. i CORRECTIVE ACTIONS:

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Immediate: OPS personnel verified proper plant response to the turbine runback l in accordance with procedure AP/1/A/5500/03. Load Rejection.

Subsequent: 1) OPS personnel secured D/G 1A and verified the Offsite Power ,

Source as required by TS.  !

2) OPS personnel reset the Transfer Trip Lockout and restored power to BLIA after consulting with the Load Dispatcher. ,

3) Power was increased to 100 percent.

6 Planned: None i

SAFETY ANALYSIS: l L

While BL1A was unavailable, the ability to safely shutdown the facility and  !

mitigate and control an accident were maintained by the avsilability of Train B i Offsite Power system and by both Unit 1 D/Gs. D/G 1A started as required on a UV l condition on ETA and would have automatically assumed the essential loads if I needed. OPS personnei made the proper notification to the NRC.

j The health and safety of the public were not affected by this incident.  !

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