Information Notice 1992-51, Misapplication and Inadequate Testing of Molded-Case Circuit Breakers

Misapplication and Inadequate Testing of Molded-Case Circuit Breakers

ML031200137
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:	07/09/1992
From:	Rossi C E Office of Nuclear Reactor Regulation
To:
References
-nr IN-92-051, NUDOCS 9207020233
Download: ML031200137 (9)

JoS / KU UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 July 9, 1992 NRC INFORMATION

NOTICE 92-51: MISAPPLICATION

AND INADEQUATE

TESTING OF MOLDED-CASE

CIRCUIT BREAKERS

Addressees

All holders of operating

licenses or construction

permits for nuclear power reactors.

Purpose

TheU.S. Nuclear Regulatory

Commission (NRC) is issuing this information

notice to alert addressees

to problems that were recently observed concerning

the application

and testing of molded-case

circuit breakers (MCCBs). 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 requirements;

therefore, no specific action or written response is required.Description

of Circumstances

During research and inspection

activities, the NRC staff has found that licensees, when determining

the MCCB parameters

for motor loads, occasionally

underestimate

or neglect to consider the inrush transient (starting)

current (ITC) occurring

during the first few cycles after a motor is started. Often only the locked rotor current (LRC) is considered

in selecting

the appropriate- MCCB.If no special starting methodology

is used to specifically

limit the ITC, the magnitude

of the ITC can be as much as approximately

three times the LRC.Also, depending

on the electrical

characteristics

of the power supply and the impedance

of the motor when started, the ITC can increase to as much as approximately

six times the value of the LRC. A current of this magnitude

is greater than the maximum instantaneous

trip setting for circuit protection

recommended

by the National Electric Code (NEC). Therefore, the NEC recommended

level of protection

may be insufficient

to prevent an unwanted trip. Proper application

of MCCBs depends strongly upon the use of accurate design assumptions.

Another application

problem involves the use of MCCBs equipped with both thermal overload trip elements and instantaneous

magnetic trip elements.

A newly purchased

replacement

Westinghouse

Type HFB3125 ambient compensating

MCCB tripped when a hydrogen skimmer fan motor at the Catawba Nuclear Station 7 9207020233

\J 1-IN 92-51 July 9, 1992 was started during testing after installation.

Duke Power Company personnel did not expect the MCCB to trip since the peak value of the ITC for the fan motor was thought to be well below the instantaneous

trip band of that MCCB (NRC Inspection

Report 99900404/90-01).

A similar Westinghouse

MCCB used as a turbine room sump pump breaker tripped in a similar manner at the Donald C. Cook Nuclear Power Plant. (NRC Inspection

Report 99900404/90-21).

Westinghouse

determined

that most of its thermal-magnetic

MCCBs with the nonadjustable

instantaneous

magnetic trip function could trip inadvertently.

Westinghouse

attributed

this behavior to interaction

between the thermal overload trip function and the instantaneous

magnetic trip function under overload conditions.

Under nonfault conditions, these functions

may interact when the circuit current causes the thermal trip element to deflect until it presses on the MCCB's tripper bar at the same time that the instantaneous

magnetic armature is vibrating

against the tripper bar. This interaction

causes the MCCB to trip.Westinghouse

notified nuclear licensees

of this problem and recommended

that they test these MCCBs in their intended circuits before releasing

them for plant operation.

Westinghouse

also stated this recommendation

on certificates

of conformance

provided with its dedicated

MCCBs sold as safety-related

items.Potential

interactions

between thermal overload and instantaneous

trip functions

can be avoided by using a special class of MCCBs that are designed specifically

for motor loads. These MCCBs include only instantaneous

magnetic trip functions

for protecting

against faults or short circuits.

The trip setpoints

are normally adjustable

and more accurate than those in thermal-magnetic MCCBs. These MCCBs, commonly referred to by the Westinghouse

term"motor circuit protectors," are intended for use in combination

with motor contactors

or starters.

Thermal overload relays contained

in the contactors

or starters provide the coordinated

protection

against overloads

and fault currents which are below the magnitude

necessary

to actuate an instantaneous

trip of the MCCB.Instances

of premature

tripping have occurred with MCCBs manufactured

by ITE-Siemens Company. The Carolina Power and Light Company, licensee for the Shearon Harris Nuclear Power Plant, found that some of the 480 volt MCCBs manufactured

by ITE-Siemens, and purchased

as commercial-grade, tripped prematurely

when tested (NRC Inspection

Report 99901177/90-01).

The licensee had purchased

these MCCBs as replacements

for some older 600 volt ITE-Siemens

MCCBs. The ITE-Siemens

Company tested the 480 volt MCCBs and found that these trips were initiated

by the MCCBs' instantaneous

magnetic trip function, when induction

motor loads were started. The manufacturer

tested the older 600 volt MCCBs and found no premature

trips. Rather, the older 600 volt MCCBs tripped at currents significantly

above the levels at which an instantaneous

trip should have occurred.

i X -X IN 92-51 July 9, 1992 The licensee's

testing of the 480 volt MCCBs was judicious.

ITE-Siemens

stated that the instantaneous

trip setpoints

of commercial

grade MCCBs-with

nonadjustable

magnetic trips are not normally-verified

at the factory.However, ITE-Siemens

and possibly other manufacturers

of MCCBs will, upon request, verify that the instantaneous

magnetic trip points of their commercial

grade MCCBs with nonadjustable

magnetic trips supplied to nuclear utilities

fall within the appropriate

design band. Nevertheless, field testing of other MCCBs may be needed to verify that their magnetic trip points occur within the-design

band (but not below the band) because other manufacturers

may not routinely

provide this verification

for commercial

grade MCCBs. For this type of MCCB, most manufacturers

check only that the MCCB will trip instantaneously, without determining

the current level at which the trip occurs.Discussion

An MCCB can render safety-related

equipment

inoperable

if it trips prematurely.

Premature

trips can result if the incorrect

MCCB is selected (and/or incorrectly

adjusted)

as a result of inadequate

analysis of the load circuit including

dynamic analysis of expected transients

when determining

ratings, settings and coordination

requirements.

Premature

trips can also-occur with properly applied and set MCCBs that are operating

out of tolerance when incorrect

bench testing methods and/or inadequate

post-installation

testing fail to detect the out of tolerance

performance.

Acceptable

testing methods and specifications

are provided in some MCCB manufacturers'

technical

publications.

Industry and professional

organizations

also provide guidance on MCCB testing methods, including

generic acceptance

criteria, in documents

such as the National Electrical

Manufacturers

Association (NEMA) Standard AB4-1991, "Guidelines

for the Inspection

and Preventive

Maintenance

of Molded Case Circuit Breakers Used in Commercial

and Industrial

Applications." It should be noted that the application

of generic field test tolerances

to the instantaneous

trip band on manufacturers'

time-current

characteristic

curves may not always ensure that the MCCBs meet plant-specific

breaker coordination, circuit protection

or technical

specification

requirements.

Testing of properly applied and set MCCBs in accordance

with industry recommended

practices

should provide reasonable

assurance

that the MCCBs'instantaneous

trip performance

is acceptable

for safety-related

applications.

IN 92-51 July 9, 1992 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 (NRR) project manager.ssi,D ide or Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

contacts:

Satish K. Aggarwal, RES (301) 492-3829 Stephen D. Alexander, NRR (301) 504-2995 Nick Fields, NRR (301) 504-1173 Attachment:

List of Recently Issued NRC Information

Notices

.-1<-'Attachment

IN 92-51 July 9, 1992 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Information

Date of Notice No. Subject Issuance Issued to 92-50 92-49 92-48 92-47 92-46 92-45 92-44 92-43 92-42 Cracking of Valves in the Condensate

Return Lines of A BWR Emer-gency Condenser

System Recent Loss or Severe Degradation

of Service Water Systems Failure of Exide Batteries

Intent

ional

Bypassing of Automatic

Actuation of Plant Protective

Features Thermo-Lag

Fire Barrier Material Special Review Team Final Report Findings, Current Fire Endurance Tests, and Ampacity Cal-culation Errors Incorrect

Relay Used in Emergency

Diesel Generator Output Breaker Control Circuitry Problems with Westing-house DS-206 and DSL-206 Type Circuit Breakers Defective

Molded Phen-olic Armature Carriers Found on Elmwood Con-tactors Fraudulent

Bolts in Seismically

Designed Walls 07/02/92 07/02/92 07/02/92 06/29/92 06/23/92 06/22/92 06/18/92 06/09/92 06/01/92 All holders for BWRs.of OLs or CPs All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.OL = Operating

License CP = Construction

Permit

IN 92-51 July 9, 1992 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 (NRR) project manager.Original Signed by Charles E. Rossi Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

contacts: Satish K. Aggarwal, RES (301) 492-3829 Stephen D. Alexander, NRR (301) 504-2995 Nick Fields, NRR (301) 504-1173 Attachment:

List of Recently Issued NRC Information

Notices Brian K. Grimes, Director, Division of Reactor Inspection

and Safeguards

and Ashok C. Thadani, Director, Division of Systems Technology

concurred

in a previous version of this information

notice. Notice was significantly

revised to remove "regulatory

guide" portions of original draft after above concurrences

were obtained.

I determined

it was unnecessary

to have re-concurrence

at the Division Director level. C. E. Rossi*SEE PREVIOUS CONCURRENCE

OEAB:DOEA:NRR

NFields*05/21/92 EMEB:DE:RES

SKAggarwal*

06/08/92 SELB:NRR ASGill*06/29/92 SC/OEAB:DOEA:NRR

DFischer*05/22/92 C/EMEB:DE:RES

MVagins*06/08/92 C/OGCB:DOEA:NRR

CHBerlinger*

06/10/92 RPB:ADM TechEd*05/22/92 D/DE:RES LCShao*06/08/92 7W ssi C/OEAB:DOEA:NRR

AChaffee*06/04/92 RVIB:NRR SAlexander*

06/30/92 Document Name: 92-51.IN

IN 92-XX June xx, 1992 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 (NRR) project manager.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

contacts: Satish K. Aggarwal, RES (301) 492-3829 Stephen D. Alexander, NRR (301) 504-2995 Nick Fields, NRR (301) 504-1173 Attachment:

List of Recently Issued NRC Information

Notices Brian K. Grimes, Director, Division of Reactor Inspection

and Safeguards

and Ashok C. Thadani, Director, Division of Systems Technology

concurred

in a previous version of this information

notice. Notice was significantly

revised to remove "regulatory

guide" portions of original draft after above %y concurrences

were obtained.

C. E. Ros i;2r B a*SE PREVIOUS CONCURe RN-*SEE PREVIOUS CONCURRENCE

OEAB:DOEA:NRR

NFields*05/21/92 EMEB:DE:RES

SKAggarwal*

06/08/92 SC/OEAB:DOEA:NRR

DFischer*05/22/92 C/EMEB:DE:RES

MVagins*06/08/92 RPB:ADM TechEd*05/22/92 D/DE:RES LCShao*06/08/92 C/OEAB:DOEA:NRR

AChaffee*06/04/92 RVIB:NRRA SAlexander

06 / 0/92 SELB:NRR ASGill*06/29/92 C/OGCB:DOEA:NRR

CHBerlinger*

06/10/92 D/DOEA:NRR

CERossi/ /92 Document Name: C:\CIRBRK (ATB)

I I IN 92-XX May xx, 1992 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 (NRR) project manager.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

contacts: Satish K. Aggarwal, RES (301) 492-3829 Stephen D. Alexander, NRR (301) 504-2995--Am itpa 1 -G-i-l1 NR (301t=043-i

Nick Fields, NRR (301) 504-1173 Attachment:

List of Recently Issued NRC Information

Notices Brian K. Grimes, Director, Division of Reactor Inspection

and Safeguards

and Ashok C. Thadani, Director, Division of Systems Technology

concurred

in a previousversion

of this informa ion no t iV >4 A/ ' N. r.t*Sv i!EE P RE VIOU SC NC OCUR'RE NC W -.)4 OEAB:DOEA:NRR

NFields*05/21/92 EMEB:DE:RES

SKAggarwal

&/ g /92 C/OGBJ NRR CHBe inger G/ Io192 SC/OEAB:DOEA:NRR

DFischer*05/22)si C/4A:RES MVagins C, /of/i92 D/DOEA:NRR

CERossi/ /92 RVIB :NRR SAlexander

06/ /92 C,- A B r-t" -RPB:ADM C/OEAB:DOEA:NRR

Tech Ed* Jt);,,4*Chaffee

05/2219 /9 / C/q/92 SELB: NR- ,, ASGill 06l97/92 Document Name: C:\CIRBRK (ATB)

I r -.'K-'IN 92-XX May xx, 1992 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 (NRR) project manager.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

contacts: Satish K. Aggarwal, RES (301) 492-3829 Stephen D. Alexander, NRR (301) 504-2995 N raS.m l G1J4INRK Nick Fields, NRR (301) 504-1173 Attachment:

List of Recently Issued NRC Information

Notices Document Name: OEAB:DOEA:.

RR NFieldsfJ Y5/h4/92 EMEB:DE:RES

SKAggarwal

/ /92 D/DST:NRR ACThadani/ /92 C:\CIRBRK (ATB)SCREAB:DOEA:NRR

DFischer 5 /7-i/92 C/EMEB:DE:RES

MVagins/ /92 C/OGCB:DOEA:NRR

CHBerlinger

/ /92 RPB:ADM TechEd/ /92 D/DE:RES LCShao/ /92 GV fo JC C/OEAB:DOEA:NRR

AChaffee G/ 5/92 D/DRIS:NRR

BKGrimes/ /92 D/DOEA:NRR

CERossi/ /92