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

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==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 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  
\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 occurre 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 application 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) 504-1173
\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.


===Attachment:===
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.
List of Recently Issued NRC Information Notices
 
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


.-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
.-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


==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 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) 504-1173
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
 
===Attachment:===
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 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) 504-1173
 
===Attachment:===
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)
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) 504-1173


===Attachment:===
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
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) 504-1173


===Attachment:===
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)
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}}
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  
}}


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Revision as of 18:50, 6 April 2018

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 E
Office of Nuclear Reactor Regulation
To:
References
-nr IN-92-051, NUDOCS 9207020233
Download: ML031200137 (9)
v • d • e


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

Addressees

All holders of operating licenses or construction permits for nuclear powerreactors.

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.

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

\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.

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.

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

.-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

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

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

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)

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


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