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 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

9207020233 7

\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

one of the technical contacts listed below or the appropriate Office contact

Nuclear Reactor Regulation (NRR) project manager. of

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 Cracking of Valves in 07/02/92 All holders of OLs or CPs

the Condensate Return for BWRs.

Lines of A BWR Emer- gency Condenser System

92-49 Recent Loss or Severe 07/02/92 All holders of OLs or CPs

Degradation of Service for nuclear power reactors.

Water Systems

92-48 Failure of Exide Batteries 07/02/92 All holders of OLs or CPs

for nuclear power reactors.

92-47

Intent

ional Bypassing 06/29/92 All holders of OLs or CPs

of Automatic Actuation for nuclear power reactors.

of Plant Protective

Features

92-46 Thermo-Lag Fire Barrier 06/23/92 All holders of OLs or CPs

Material Special Review for nuclear power reactors.

Team Final Report Findings, Current Fire Endurance

Tests, and Ampacity Cal- culation Errors

92-45 Incorrect Relay Used in 06/22/92 All holders of OLs or CPs

Emergency Diesel Generator for nuclear power reactors.

Output Breaker Control

Circuitry

92-44 Problems with Westing- 06/18/92 All holders of OLs or CPs

house DS-206 and DSL-206 for nuclear power reactors.

Type Circuit Breakers

92-43 Defective Molded Phen- 06/09/92 All holders of OLs or CPs

olic Armature Carriers for nuclear power reactors.

Found on Elmwood Con- tactors

92-42 Fraudulent Bolts in 06/01/92 All holders of OLs or CPs

Seismically Designed for nuclear power reactors.

Walls

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 SC/OEAB:DOEA:NRR RPB:ADM C/OEAB:DOEA:NRR

NFields* DFischer* TechEd* AChaffee*

05/21/92 05/22/92 05/22/92 06/04/92 EMEB:DE:RES C/EMEB:DE:RES D/DE:RES RVIB:NRR

SKAggarwal* MVagins* LCShao* SAlexander*

06/08/92 06/08/92 06/08/92 06/30/92 SELB:NRR C/OGCB:DOEA:NRR 7W ssi

ASGill* CHBerlinger*

06/29/92 06/10/92 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 SC/OEAB:DOEA:NRR RPB:ADM C/OEAB:DOEA:NRR

NFields* DFischer* TechEd* AChaffee*

05/21/92 05/22/92 05/22/92 06/04/92 EMEB:DE:RES C/EMEB:DE:RES D/DE:RES RVIB:NRRA

SKAggarwal* MVagins* LCShao* SAlexander

06/08/92 06/08/92 06/08/92 06 / 0/92 SELB:NRR C/OGCB:DOEA:NRR D/DOEA:NRR

ASGill* CHBerlinger* CERossi

06/29/92 06/10/92 / /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

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(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 noiVt > 4 A/ N.

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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: C:\CIRBRK (ATB)

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