Information Notice 1991-57, Operational Experience on Bus Transfers

Operational Experience on Bus Transfers

ML031190290
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	09/19/1991
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-91-057, NUDOCS 9109130190
Download: ML031190290 (8)

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-1i UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555

' September 19, 1991

-NRC INFORMATION NOTICE 91-57: OPERATIONAL EXPERIENCE ON BUS TRANSFERS

Addressees

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All holders of operating licenses or construction permits for 'nuclear power

reactors. -

Purpose

'

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice

to alert addressees to findings contained in Engineering Evaluation Report

AEOD/E90-05, "Operational Experience on Bus Transfer'," June 199D, on medium- voltage (2 kV to 15 kV) bus transfer failures-at nuclear power reactors. It is

expected that recipients will review the information for applicability to 'their

facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this information notice are not NRC require- ments; therefore, no specific action or written response is required.

Description of Circumstances

In 1988 and 1989, Northeast Utilities issued licensee event reports (LERs)'

50-422/88-026 and 50-422/89-030 indicating that at the Millstone Nuclear Power

Station,!Unit 3, under certain scenarios, the existing'bus transfer scheme

could result in common-mode failure of ClasslE loads of both trains, and

repeated bus transfers could damage the safety-related motors'.' This informa- tion prompted the NRC to conduct an-in-depth study of the bus transfer prac- tices and operational experience at U.S. nuclear plants. The results of this

study are delineated in NRC Engineering Evaluation Report AEOD/E90-05,

"Operational Experience on Bus Transfer," June 1990. The report indicates

that between 1985 and 1989 bus-transfers either failed to take place on demand

or were accompanied by some'equipment- malfunction-on more than 50 occasions.

Discussion

The problems associated with the bus transfer process raise two basic safety

concerns:

(1) Damage to the equipment connected to the auxiliary buses.

(2): -Failures of bus transfers to take place on demand.

The first safety-concern.relates to an excessive difference in voltage between

the auxiliary load bus and the incoming-power source. An excessive voltage

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IN 91-57 September 19, 1991 difference will cause transient current flows in the system that candamage the

transformers, the buses, and theWconnected loads.

There is.a differen~ce of opinion within the industry about criteria that-assure

safe bus transfer. In 1977, 'the Americtrr National Stridards Institute (ANSI)

introduced the recommendation for limiting resultant voltage to 1.33 per unit

volts per hertz by issuing ANSI standard C50.41, "Polyphase Induction Motors

for Power Generating Stations." The National Electrical Manufacturers Associa- tion (NEMA) accepted this as a safe criteriQnin NEMA MG-1-1978, "Motors.and

Generators."' However,further research showed that limiting the resultant

voltage to 1.33 per unit volts per hertz does not ensure that motor shaft

torques will be within acceptable limits. In 1987, NEMA withdrew the criterion

from MG-1.

The NRC staff is not aware of equipment failures at..nuclear plaIts that, can be

directly attributed to eXce'ssive' difference' in'voltage between an auxiliary

load"'bus and the incomihg.power, source, although some equipment could be

stressed U this pr6cess.' Such stresses experienced by connected equipment

would be. cumula'ti've,: and',' uinless specifki action is taken.to limit' these

stresses',they can remainj'undetectedi.ntit failure'occurs.

The second safety'concern cov'ers cases in whi ch the transfer does not take

place on demand, resulting in a loss of power to buses. In.most nuclear;.

plants, such a failure leads to the loss of offsitepower to plant auxiliary

loads-,-which-n-some-cases,-include-the-Class--IE loads. Hence, with-this-.type- of bu's-transfer'failUre,';th'e Clas's'lE lo'ads-will be powered by. the.emergency.

diese1 gerntor's, and 7reactor sstem coblin will be .accomplished by-natural

circul'ation. Althobgh nu-clear plaants ati d'signed to safely shut down.on a

loss of'offslteepower, it is desirable' th4't such failures be kept to a minimum.

to m'finiiize;c'hllen'gesto the' emerg ency dese6lgenerators.:

Analy`sisii z ,

The data fror AtODIE190-65, ind'i'cttes'that the' irot causes for.the most signifi

caiet'events (those that% in'ved'ln'aotual fa'il.re to'. transfer or a significant

design deficienky) canb- 6eb'roken down as follows:' c'

42 percent were caused by design deficiencies, i

25'-percent were'caused by equi pment failures

18 percent were c persnneel ererors and

15 percent were caused by protective relays thqt blockedthe bus transfer, The major design deficiencies.includIed slot bus~transfer,(35 percent of

designudef-ciency:events), 1ow bsv61tagef(.4percent f all design deficiency all

n speed'of operation of sync-check relays

(17 percent of all design deficiency events).

IN 91-57 September 19, 1991 In addition, the report includes a discussion of various design modifications

that can reduce the-probability of bus-transfer failures,-including modifying

the power distribution scheme, using'static.sync-check relays And devices, and

incorporating faster bus trainsfer practices. The report also Indicates that'

many of the bus transfer failures resulting'from equipment malfunction and

personnel errors can be avoided by improving equipment maintenance and person- nel vigilance.,:

Related Generic Communications

The staff has issued the following information notices on this and related

topics: Information Notices 85-28, "Partial Loss of AC Power and Dfes&i

Generator Degradation,"86-87, "Loss of Offsite Power Upon an AutomaticjBus

Transfer,"86-100, "Loss of Offstte Power to Vital .Buses at Salem:2," and

88-50, "Effect of Circuit.Breaker Capacitance on.Availab.ility of Emergency

Power." . .-

NRC Engineering Evaluation Report-AEOD/E90-05 is available n.-the Public

Document Room', Washington, D.C. (Accession Number 9007310012).

This information notice requires no specific action or written response. If

you have any questions.about the information-in this notice, please contact one

of the technical cohtacts listed below'or the appropriate Office of Nuclear I .

Reactor Regulation project manager. . . .... .- -; i _.s

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X__F_~).<55/Xe

Division of Operational E

Office of Nuclear Reactor Regulation

. r r ' ;.2 Technical contacts: Subinoy Mazumdar, AEOD

(301) 492-4308 Andrew Kugler, NRR

(301) 492-0834 .

Attachment:

List of Recently Issued NRC Information Notices

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U-M IN 91-57 Septaber 19. 1991 Pp I eot 1

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.,I .4 LIST Of MCENTLY ISSUED'

IRC IUKMfOaTIQIU NOTICES

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Infermetion Bate of

Subject Issuance Issued to

-

Potential Radiotive 09/1S/91 ill ,holders of A0S or CPs

91-55, Lekage to TniK Vented

to Atmosphee -

'for puclear power reactors.

(

Failures Ceusatb An: 09/16/1 All holdre' of OLt or CPs

Improperly Adjustkd Test fori nuclear tower reactors.

L-ink In 4.16'V General

Electric Switchioar"

05-18, Failures of Undervoltae 09/10/91 All holders'of OLS or CPSfor

'Output Circuit Bfds In Wdest~inghouse (40-designed

the Westinghoee-Oesigned nucear. power reactors.

Splid State Protect4oh

Syltam

,91-54 Foreign Experience Regard- 09/06/91 All holders. o-OLs or CPs

ng Baoron Ollution for pressurized water

reactors (?irr.

Pressurizer Saf ty Valve ' 09/05/91 All hIolersot OLs- or CPs

Lift Setpoint Sbift ore nclaar poweIrsrectorS.

Fellure of Remote Shutd&wn 09/04/91 All oofdsrs or CPs

eOLs

System Instramentation for ulr power reactors.

Because of Incorrectly

'lnstalled Components

91-52 kooconservative Errors 0829/0/91 AI holders of OLs or CPs

In. Overtemperature Delte- for Uestiflghousa (W)-designed

Temperature (0Tot) Set- nuclearpoear reaetors.

point Caused by Improper

Goin Settings

W614, 0826/91 All holders of'OLe or CPa

Overspead Trips of AFW.

NIPCI end RCIC Turbines' for nuclear power feectors.

91-41 Inadequate Fuse Centrol 08/20/91 All holders eof 0L or CPs

Progre for nuclear power reactors.

OL

• Operatin License I

CP u Construction Permit

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- IN 91-57 September 19, 1991 In addition, the report includes a discussion of various design modifications

that can reduce the probability of bus transfer failures, including modifying

the power distribution scheme, using static sync-check relays and devices, and

incorporating faster bus transfer practices. The report also indicates that

many of the bus transfer failures resulting from equipment malfunction and

personnel errors can be avoided by improving equipment maintenance and person- nel vigilance.

Related Generic Communications

The staff has issued the following information notices on this and related

topics: Information Notices 85-28, "Partial Loss of AC Power and Diesel

Generator Degradation," 86-87, "Loss of Offsite Power Upon an Automatic Bus

Transfer,"86-100, "Loss of Offsite Power to Vital Buses at Salem 2," and

88-50, "Effect of Circuit Breaker Capacitance on Availability of Emergency

Power."

NRC Engineering Evaluation Report AEOD/E90-05 is available in the Public

Document Room, Washington, D.C. (Accession Number 9007310012).

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact one

of the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

Original Signed by

Charles F.Rossi

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: Subinoy Mazumdar, AEOD

(301) 492-4308 Andrew Kugler, NRR

(301) 492-0834 Attachment:

List of Recently Issued NRC Information Notices

• SEE PREVIOUS CONCURRENCS

D/ D /OGCB:DOEA:NRR*RPB:ADM *C/SELB:DST:NRR

CeD L/( CHBerlinger TechEd FRosa

9//'91 i 8/26/91 06/28/91 09/11/91

• OGCB:DOEA:NRR*ROA l3SP:AEOD

• I3AB:DSP:AEOD *C/ROAB:DSP:AEOD *D/DSP:NRR

AJKugler SMazumdar EJBrown JERosenthal TMNovak

08/08/91 08/09/91 08/13/91 08/13/91 08/19/91 DOCUMENT NAME: IN 91-57

IN 91-XX

September xx, 1991 In addition, the report includes a discussion of various design modifications

that can reduce the probability of bus transfer failures, including modifying

the power distribution scheme, using static sync-check relays and devices, and

incorporating faster bus transfer practices. The report also indicates that

many of the bus transfer failures resulting from equipment malfunction and

personnel errors can be avoided by improving equipment maintenance and person- nel vigilance.

Related Generic Communications

The staff has issued the following information notices on this and related

topics: Information Notices 85-28, "Partial Loss of AC Power and Diesel

Generator Degradation," 86-87, "Loss of Offsite Power Upon an Automatic Bus

Transfer,"86-100, "Loss of Offsite Power to Vital Buses at Salem 2," and

88-50, "Effect of Circuit Breaker Capacitance on Availability of Emergency

Power."

This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact one

of the technical contacts listed below or the appropriate Office of Nuclear

Reactor Regulation project manager.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical contacts: Subinoy Mazumdar, AEOD

(301) 492-4308 Andrew Kugler, NRR

(301) 492-0834 References:

Ie NRC Engineering Evaluation Report, AEOD/E90-05,

"Operational Experience On Bus Transfers," June 1990.

Available in the Public Document Room, Washington, D.C.,

Accession Number 9007310012 Attachment:

List of Recently Issued NRC Information Notices

Document Name: BUS TRANSFER IN

• SEE PREVIOUS CONCURRENCES

D/DOEA:NRO

CERossi

• C/OGCB:DOEA:NRR*RPB:ADM

CHBerlinger TechEd 04~osa

ti/SEL?.DS'T:NRR

09/ /91V 08/26/91 06/28/91 09/:{ /91

• OGCB:DOIPA:NRR*ROAB:DSP:AEOD *ROAB:DSP:AEOD *C/ROAB:DSP:AEOD *D/DSP:NRR

AJKugler S)IM ndar EJBrown JERosenthal TMNovak

08/08/91 08/69/9^1 08/13/91 08/13/91 08/19/91

IN 91-XX

August xx, 1991 In addition, the report includes a discussion of various design modifications

that can reduce the probability of bus transfer failures, including modifying and

the power distribution scheme, using static sync-check relays and devices, practices. The report also indicates that

incorporating faster bus transfer

many of the bus transfer failures resulting from equipment malfunction and

personnel errors can be avoided by improving equipment maintenance and person- nel vigilance.

Related Generic Communications

The staff has issued the following information notices on this and related

topics: Notices 85-28, "Partial Loss of AC Power and Diesel Generator Degrada- tion," 86-87, "Loss of Offsite Power Upon an Automatic Bus Transfer,"86-100,

"Loss of Offsite Power to Vital Buses at Salem 2," and 88-50, "Effect of

Circuit Breaker Capacitance on Availability of Emergency Power."

If

This information notice requires no specific action or written response. one

you have any questions about the information in this notice, please contact

manager.

of the technical contacts listed below or the! appropriate NRR project

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Subinoy Mazumdar, AEOD

(301) 492-4308 Andrew Kugler, NRR

(301) 492-0834 Attachment:

List of Recently Issued NRC Information Notices

References:

1. NRC Engineering Evaluation Report, AEOD/E90-05,

"Operational Experience On Bus Transfers," June 1990.

Document Name: BUS TRANSFER IN

D/DOEA:N1t C/OG  : NRR *RPB:ADM

CERossSI CHBerlinger TechEd

08/ /911 08/Z&91 06/28/91 OGCB:DOEA:NRR ROAB: C)SP:A OD ROAB:DSPAEOD C/ROAB:DSP:AI); D/Di RR

AJKuglerclK SMazurnda ; EJBrown !? JERosenthal

08//3/91 08//3'91 08/l ¶191

08/ ,/91" 08/ 9i/91

.

also indicates that many of the transfer failures resulting from equipment

malfunction and personnel errors can be avoided by improving equipment

maintenance and personnel vigilance.

Related Generic Communications

Previous information notices have been issued on this and related topics.

Notices 85-28, Partial Loss of AC Power and Diesel Generator Degradation."

86-87, "Loss of Offsite Power Upon an Automatic Bus Transfer,"86-100, "Loss

of Offsite Power to Vital Buses at Salem 2," and 88-50, 'effect of Circuit

Breaker Capacitance on Availability of Emergency Power" should be consulted

for further information.

No specific action is required by the notice. However, if you have any

questions on this issue, please contact the technical staff listed below or

the regional administrator of the appropriate regional office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts: Subinoy Mazumdar, AEOD

(301) 492-4308 Andrew Kugler, NRR

(301) 492-0834 Attachments:

List of Recently Issued NRC Information Notices

References:

1. NRC Engineering Evaluation Report, AEOD/E90-05, "Operational

Experience On Bus Transfers, June 1990.

D/DOEA:NRR C/OGCB:DOEA:NRR

CERossi CHBerlinger

07/ 91 07/ /91 OGCB:DOEA:NRR ROAB:DSP:AEOD C/ROABtDSP:AEOD D/DSP:AEOD RPB:ADM

AJKugler v SMazumdar JERosenthal TMNovak TechEd

06/12./91 06/ /91 06/ /91 06/ /91 06/21 /91

)1Nin 91h