Information Notice 1992-51, Misapplication and Inadequate Testing of Molded-Case Circuit Breakers: Difference between revisions

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| issue date = 07/09/1992
| issue date = 07/09/1992
| title = Misapplication and Inadequate Testing of Molded-Case Circuit Breakers
| title = Misapplication and Inadequate Testing of Molded-Case Circuit Breakers
| author name = Rossi C E
| author name = Rossi C
| author affiliation = NRC/NRR
| author affiliation = NRC/NRR
| addressee name =  
| addressee name =  
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| page count = 9
| page count = 9
}}
}}
{{#Wiki_filter:JoS / KUUNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555July 9, 1992NRC INFORMATION NOTICE 92-51: MISAPPLICATION AND INADEQUATE TESTINGOF MOLDED-CASE CIRCUIT BREAKERS
{{#Wiki_filter: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==
==Addressees==
All holders of operating licenses or construction permits for nuclear powerreactors.
All holders of operating licenses or construction permits for nuclear power
 
reactors.


==Purpose==
==Purpose==
TheU.S. Nuclear Regulatory Commission (NRC) is issuing this informationnotice to alert addressees to problems that were recently observed concerningthe application and testing of molded-case circuit breakers (MCCBs). It isexpected that recipients will review the information for applicability totheir facilities and consider actions, as appropriate, to avoid similarproblems. However, suggestions contained in this information notice are notNRC requirements; therefore, no specific action or written response isrequired.
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==
==Description of Circumstances==
During research and inspection activities, the NRC staff has found thatlicensees, when determining the MCCB parameters for motor loads, occasionallyunderestimate or neglect to consider the inrush transient (starting) current(ITC) occurring during the first few cycles after a motor is started. Oftenonly the locked rotor current (LRC) is considered in selecting the appropriate-MCCB.If no special starting methodology is used to specifically limit the ITC, themagnitude of the ITC can be as much as approximately three times the LRC.Also, depending on the electrical characteristics of the power supply and theimpedance of the motor when started, the ITC can increase to as much asapproximately six times the value of the LRC. A current of this magnitude isgreater than the maximum instantaneous trip setting for circuit protectionrecommended by the National Electric Code (NEC). Therefore, the NECrecommended level of protection may be insufficient to prevent an unwantedtrip. Proper application of MCCBs depends strongly upon the use of accuratedesign assumptions.Another application problem involves the use of MCCBs equipped with boththermal overload trip elements and instantaneous magnetic trip elements. Anewly purchased replacement Westinghouse Type HFB3125 ambient compensatingMCCB tripped when a hydrogen skimmer fan motor at the Catawba Nuclear Station7 9207020233  
During research and inspection activities, the NRC staff has found that
\J 1-IN 92-51July 9, 1992 was started during testing after installation. Duke Power Company personneldid not expect the MCCB to trip since the peak value of the ITC for the fanmotor was thought to be well below the instantaneous trip band of that MCCB(NRC Inspection Report 99900404/90-01). A similar Westinghouse MCCB usedas a turbine room sump pump breaker tripped in a similar manner at theDonald C. Cook Nuclear Power Plant. (NRC Inspection Report 99900404/90-21).Westinghouse determined that most of its thermal-magnetic MCCBs with thenonadjustable instantaneous magnetic trip function could trip inadvertently.Westinghouse attributed this behavior to interaction between the thermaloverload trip function and the instantaneous magnetic trip function underoverload conditions. Under nonfault conditions, these functions may interactwhen the circuit current causes the thermal trip element to deflect until itpresses on the MCCB's tripper bar at the same time that the instantaneousmagnetic armature is vibrating against the tripper bar. This interactioncauses the MCCB to trip.Westinghouse notified nuclear licensees of this problem and recommended thatthey test these MCCBs in their intended circuits before releasing them forplant operation. Westinghouse also stated this recommendation on certificatesof conformance provided with its dedicated MCCBs sold as safety-related items.Potential interactions between thermal overload and instantaneous tripfunctions can be avoided by using a special class of MCCBs that are designedspecifically for motor loads. These MCCBs include only instantaneous magnetictrip functions for protecting against faults or short circuits. The tripsetpoints 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 motorcontactors or starters. Thermal overload relays contained in the contactorsor starters provide the coordinated protection against overloads and faultcurrents which are below the magnitude necessary to actuate an instantaneoustrip of the MCCB.Instances of premature tripping have occurred with MCCBs manufactured by ITE-Siemens Company. The Carolina Power and Light Company, licensee for theShearon Harris Nuclear Power Plant, found that some of the 480 volt MCCBsmanufactured by ITE-Siemens, and purchased as commercial-grade, trippedprematurely when tested (NRC Inspection Report 99901177/90-01). The licenseehad purchased these MCCBs as replacements for some older 600 volt ITE-SiemensMCCBs. The ITE-Siemens Company tested the 480 volt MCCBs and found that thesetrips were initiated by the MCCBs' instantaneous magnetic trip function, wheninduction motor loads were started. The manufacturer tested the older 600volt MCCBs and found no premature trips. Rather, the older 600 volt MCCBstripped at currents significantly above the levels at which an instantaneoustrip should have occurred.
 
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


i X -XIN 92-51July 9, 1992 The licensee's testing of the 480 volt MCCBs was judicious. ITE-Siemensstated that the instantaneous trip setpoints of commercial grade MCCBs-withnonadjustable magnetic trips are not normally-verified at the factory.However, ITE-Siemens and possibly other manufacturers of MCCBs will, uponrequest, verify that the instantaneous magnetic trip points of theircommercial grade MCCBs with nonadjustable magnetic trips supplied to nuclearutilities fall within the appropriate design band. Nevertheless, fieldtesting of other MCCBs may be needed to verify that their magnetic trip pointsoccur within the-design band (but not below the band) because othermanufacturers may not routinely provide this verification for commercial gradeMCCBs. For this type of MCCB, most manufacturers check only that the MCCBwill trip instantaneously, without determining the current level at which thetrip occurs.DiscussionAn MCCB can render safety-related equipment inoperable if it tripsprematurely. Premature trips can result if the incorrect MCCB is selected(and/or incorrectly adjusted) as a result of inadequate analysis of the loadcircuit including dynamic analysis of expected transients when determiningratings, settings and coordination requirements. Premature trips can also-occur with properly applied and set MCCBs that are operating out of tolerancewhen incorrect bench testing methods and/or inadequate post-installationtesting fail to detect the out of tolerance performance.Acceptable testing methods and specifications are provided in some MCCBmanufacturers' technical publications. Industry and professionalorganizations also provide guidance on MCCB testing methods, including genericacceptance criteria, in documents such as the National ElectricalManufacturers Association (NEMA) Standard AB4-1991, "Guidelines for theInspection and Preventive Maintenance of Molded Case Circuit Breakers Used inCommercial and Industrial Applications." It should be noted that theapplication of generic field test tolerances to the instantaneous trip band onmanufacturers' time-current characteristic curves may not always ensure thatthe MCCBs meet plant-specific breaker coordination, circuit protection ortechnical specification requirements.Testing of properly applied and set MCCBs in accordance with industryrecommended practices should provide reasonable assurance that the MCCBs'instantaneous trip performance is acceptable for safety-related applications.
92-48            Failure of Exide Batteries    07/02/92      All holders of OLs or CPs


IN 92-51July 9, 1992 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.ssi,D ide orDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts: Satish K. Aggarwal, RES(301) 492-3829Stephen D. Alexander, NRR(301) 504-2995Nick Fields, NRR(301) 504-1173Attachment:List of Recently Issued NRC Information Notices
for nuclear power reactors.


.-1<-'AttachmentIN 92-51July 9, 1992 LIST OF RECENTLY ISSUEDNRC INFORMATION NOTICESInformation Date ofNotice No. Subject Issuance Issued to92-5092-4992-4892-4792-4692-4592-4492-4392-42Cracking of Valves inthe Condensate ReturnLines of A BWR Emer-gency Condenser SystemRecent Loss or SevereDegradation of ServiceWater SystemsFailure of Exide Batteries
92-47           


==Intent==
==Intent==
ional Bypassingof Automatic Actuationof Plant ProtectiveFeaturesThermo-Lag Fire BarrierMaterial Special ReviewTeam Final Report Findings,Current Fire EnduranceTests, and Ampacity Cal-culation ErrorsIncorrect Relay Used inEmergency Diesel GeneratorOutput Breaker ControlCircuitryProblems with Westing-house DS-206 and DSL-206Type Circuit BreakersDefective Molded Phen-olic Armature CarriersFound on Elmwood Con-tactorsFraudulent Bolts inSeismically DesignedWalls07/02/9207/02/9207/02/9206/29/9206/23/9206/22/9206/18/9206/09/9206/01/92All holdersfor BWRs.of OLs or CPsAll holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.All holders of OLs or CPsfor nuclear power reactors.OL = Operating LicenseCP = Construction Permit
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


IN 92-51July 9, 1992 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Original Signed byCharles E. RossiCharles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts:Satish K. Aggarwal, RES(301) 492-3829Stephen D. Alexander, NRR(301) 504-2995Nick Fields, NRR(301) 504-1173Attachment:List of Recently Issued NRC Information NoticesBrian K. Grimes, Director, Division of Reactor Inspection and Safeguardsand Ashok C. Thadani, Director, Division of Systems Technology concurred in aprevious version of this information notice. Notice was significantly revisedto remove "regulatory guide" portions of original draft after aboveconcurrences were obtained. I determined it was unnecessary to have re-concurrence at the Division Director level. C. E. Rossi*SEE PREVIOUS CONCURRENCEOEAB:DOEA:NRRNFields*05/21/92EMEB:DE:RESSKAggarwal*06/08/92SELB:NRRASGill*06/29/92SC/OEAB:DOEA:NRRDFischer*05/22/92C/EMEB:DE:RESMVagins*06/08/92C/OGCB:DOEA:NRRCHBerlinger*06/10/92RPB:ADMTechEd*05/22/92D/DE:RESLCShao*06/08/927W ssiC/OEAB:DOEA:NRRAChaffee*06/04/92RVIB:NRRSAlexander*06/30/92Document Name: 92-51.IN
*SEE PREVIOUS CONCURRENCE


IN 92-XXJune xx, 1992 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts:Satish K. Aggarwal, RES(301) 492-3829Stephen D. Alexander, NRR(301) 504-2995Nick Fields, NRR(301) 504-1173Attachment:List of Recently Issued NRC Information NoticesBrian K. Grimes, Director, Division of Reactor Inspection and Safeguardsand Ashok C. Thadani, Director, Division of Systems Technology concurred in aprevious version of this information notice. Notice was significantly revisedto remove "regulatory guide" portions of original draft after above %yconcurrences were obtained. C. E. Ros i;2r B a*SE PREVIOUS CONCURe RN-*SEE PREVIOUS CONCURRENCEOEAB:DOEA:NRRNFields*05/21/92EMEB:DE:RESSKAggarwal*06/08/92SC/OEAB:DOEA:NRRDFischer*05/22/92C/EMEB:DE:RESMVagins*06/08/92RPB:ADMTechEd*05/22/92D/DE:RESLCShao*06/08/92C/OEAB:DOEA:NRRAChaffee*06/04/92RVIB:NRRASAlexander06 / 0/92SELB:NRRASGill*06/29/92C/OGCB:DOEA:NRRCHBerlinger*06/10/92D/DOEA:NRRCERossi/ /92Document Name: C:\CIRBRK(ATB)  
OEAB:DOEA:NRR        SC/OEAB:DOEA:NRR            RPB:ADM      C/OEAB:DOEA:NRR
I IIN 92-XXMay xx, 1992 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts:Satish K. Aggarwal, RES(301) 492-3829Stephen D. Alexander, NRR(301) 504-2995--Am itpa 1 -G-i-l1 NR(301t=043-iNick Fields, NRR(301) 504-1173Attachment: List of Recently Issued NRC Information NoticesBrian K. Grimes, Director, Division of Reactor Inspection and Safeguardsand Ashok C. Thadani, Director, Division of Systems Technology concurred in apreviousversion of this informa ion no t iV >4A/ ' N. r.t*Sv i!EE P RE VIOU SC NC OCUR'RE NC W -.)4OEAB:DOEA:NRRNFields*05/21/92EMEB:DE:RESSKAggarwal&/ g /92C/OGBJ NRRCHBe ingerG/ Io192SC/OEAB:DOEA:NRRDFischer*05/22)siC/4A:RESMVaginsC, /of/i92D/DOEA:NRRCERossi/ /92RVIB :NRRSAlexander06/ /92C,- A B r-t" -RPB:ADM C/OEAB:DOEA:NRRTech Ed* Jt);,,4*Chaffee05/2219 /9 / C/q/92SELB: NR- ,,ASGill06l97/92Document Name:C:\CIRBRK (ATB)  
 
I r -.'K-'IN 92-XXMay xx, 1992 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactone of the technical contacts listed below or the appropriate Office ofNuclear Reactor Regulation (NRR) project manager.Charles E. Rossi, DirectorDivision of Operational Events AssessmentOffice of Nuclear Reactor RegulationTechnical contacts:Satish K. Aggarwal, RES(301) 492-3829Stephen D. Alexander, NRR(301) 504-2995N raS.m l G1J4INRKNick Fields, NRR(301) 504-1173Attachment: List of Recently Issued NRC Information NoticesDocument Name:OEAB:DOEA:. RRNFieldsfJY5/h4/92EMEB:DE:RESSKAggarwal/ /92D/DST:NRRACThadani/ /92C:\CIRBRK (ATB)SCREAB:DOEA:NRRDFischer5 /7-i/92C/EMEB:DE:RESMVagins/ /92C/OGCB:DOEA:NRRCHBerlinger/ /92RPB:ADMTechEd/ /92D/DE:RESLCShao/ /92GV fo JCC/OEAB:DOEA:NRRAChaffeeG/ 5/92D/DRIS:NRRBKGrimes/ /92D/DOEA:NRRCERossi/ /92  
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
                          --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 noiVt            > 4 A/ N.
 
'  r.t
 
*Sv PRE VIOU SC NC
 
i!EE             OCUR'RENC                                                  -. W
 
C,- A B r-t"-
      OEAB:DOEA:NRR        SC/OEAB:DOEA:NRR              RPB:ADM         C/OEAB:DOEA:NRR
 
NFields*              DFischer*                    Tech Ed* Jt);,,4*Chaffee
 
05/21/92              05/22)si                      05/2219 /9 / C/q/92 EMEB:DE:RES          C/4A:RES                                  RVIB :NRR      SELB: NR- ,,
                                                                      SAlexander    ASGill
 
SKAggarwal            MVagins
 
)4  &/ g /92            C, /of/i92                                06/  /92      06l97/92 C/OGBJ      NRR      D/DOEA:NRR
 
CHBe inger            CERossi
 
G/ Io192              / /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: C:\CIRBRK      (ATB)
                                                                        GV fo JC
 
OEAB:DOEA:. RR      SCREAB:DOEA:NRR          RPB:ADM        C/OEAB:DOEA:NRR
 
NFieldsfJ            DFischer                  TechEd        AChaffee
 
Y5/h4/92            5 /7-i/92                  / /92        G/ 5/92 EMEB:DE:RES          C/EMEB:DE:RES            D/DE:RES      D/DRIS:NRR
 
SKAggarwal          MVagins                  LCShao        BKGrimes
 
/ /92                / /92                    / /92          / /92 D/DST:NRR            C/OGCB:DOEA:NRR          D/DOEA:NRR
 
ACThadani            CHBerlinger              CERossi
 
/ /92                / /92                    / /92}}


{{Information notice-Nav}}
{{Information notice-Nav}}

Latest revision as of 03:23, 24 November 2019

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  Entergy icon.png
Issue date: 07/09/1992
From: Rossi C
Office of Nuclear Reactor Regulation
To:
References
-nr IN-92-051, NUDOCS 9207020233
Download: ML031200137 (9)
v • d • e


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

--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 noiVt > 4 A/ N.

' r.t

  • Sv PRE VIOU SC NC

i!EE OCUR'RENC -. W

C,- A B r-t"-

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

NFields* DFischer* Tech Ed* Jt);,,4*Chaffee

05/21/92 05/22)si 05/2219 /9 / C/q/92 EMEB:DE:RES C/4A:RES RVIB :NRR SELB: NR- ,,

SAlexander ASGill

SKAggarwal MVagins

)4 &/ g /92 C, /of/i92 06/ /92 06l97/92 C/OGBJ NRR D/DOEA:NRR

CHBe inger CERossi

G/ Io192 / /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: C:\CIRBRK (ATB)

GV fo JC

OEAB:DOEA:. RR SCREAB:DOEA:NRR RPB:ADM C/OEAB:DOEA:NRR

NFieldsfJ DFischer TechEd AChaffee

Y5/h4/92 5 /7-i/92 / /92 G/ 5/92 EMEB:DE:RES C/EMEB:DE:RES D/DE:RES D/DRIS:NRR

SKAggarwal MVagins LCShao BKGrimes

/ /92 / /92 / /92 / /92 D/DST:NRR C/OGCB:DOEA:NRR D/DOEA:NRR

ACThadani CHBerlinger CERossi

/ /92 / /92 / /92


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