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 / KU UNITED STATES NUCLEAR REGULATORY
{{#Wiki_filter:JoS                     /                             KU


COMMISSION
UNITED STATES


===OFFICE OF NUCLEAR REACTOR REGULATION===
NUCLEAR REGULATORY COMMISSION
WASHINGTON, D.C. 20555 July 9, 1992 NRC INFORMATION


NOTICE 92-51: MISAPPLICATION
OFFICE OF NUCLEAR REACTOR REGULATION


AND INADEQUATE
WASHINGTON, D.C. 20555 July 9, 1992 NRC INFORMATION NOTICE 92-51:    MISAPPLICATION AND INADEQUATE TESTING


TESTING OF MOLDED-CASE
OF MOLDED-CASE CIRCUIT BREAKERS
 
CIRCUIT BREAKERS


==Addressees==
==Addressees==
All holders of operating
All holders of operating licenses or construction permits for nuclear power
 
licenses or construction


permits for nuclear power reactors.
reactors.


==Purpose==
==Purpose==
TheU.S. Nuclear Regulatory
TheU.S. Nuclear Regulatory Commission (NRC) is issuing this information


Commission (NRC) is issuing this information
notice to alert addressees to problems that were recently observed concerning


notice to alert addressees
the application and testing of molded-case circuit breakers (MCCBs). It is


to problems that were recently observed concerning
expected that recipients will review the information for applicability to


the application
their facilities and consider actions, as appropriate, to avoid similar


and testing of molded-case
problems. However, suggestions contained in this information notice are not


circuit breakers (MCCBs). It is expected that recipients
NRC requirements; therefore, no specific action or written response is


will review the information
required.


for applicability
==Description of Circumstances==
During research and inspection activities, the NRC staff has found that


to their facilities
licensees, when determining the MCCB parameters for motor loads, occasionally


and consider actions, as appropriate, to avoid similar problems.
underestimate or neglect to consider the inrush transient (starting) current


However, suggestions
(ITC) occurring during the first few cycles after a motor is started. Often


contained
only the locked rotor current (LRC) is considered in selecting the appropriate- MCCB.


in this information
If no special starting methodology is used to specifically limit the ITC, the


notice are not NRC requirements;
magnitude of the ITC can be as much as approximately three times the LRC.
therefore, no specific action or written response is required.Description


of Circumstances
Also, depending on the electrical characteristics of the power supply and the


During research and inspection
impedance of the motor when started, the ITC can increase to as much as


activities, the NRC staff has found that licensees, when determining
approximately six times the value of the LRC. A current of this magnitude is


the MCCB parameters
greater than the maximum instantaneous trip setting for circuit protection


for motor loads, occasionally
recommended by the National Electric Code (NEC). Therefore, the NEC


underestimate
recommended level of protection may be insufficient to prevent an unwanted


or neglect to consider the inrush transient (starting)
trip. Proper application of MCCBs depends strongly upon the use of accurate
current (ITC) occurring


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


in selecting
Another application problem involves the use of MCCBs equipped with both


the appropriate- MCCB.If no special starting methodology
thermal overload trip elements and instantaneous magnetic trip elements. A


is used to specifically
newly purchased replacement Westinghouse Type HFB3125 ambient compensating


limit the ITC, the magnitude
MCCB tripped when a hydrogen skimmer fan motor at the Catawba Nuclear Station


of the ITC can be as much as approximately
9207020233                                                      7


three times the LRC.Also, depending
\J                                      1- IN 92-51 July 9, 1992 was started during testing after installation. Duke Power Company personnel


on the electrical
did not expect the MCCB to trip since the peak value of the ITC for the fan


characteristics
motor was thought to be well below the instantaneous trip band of that MCCB


of the power supply and the impedance
(NRC Inspection Report 99900404/90-01). A similar Westinghouse MCCB used


of the motor when started, the ITC can increase to as much as approximately
as a turbine room sump pump breaker tripped in a similar manner at the


six times the value of the LRC. A current of this magnitude
Donald C. Cook Nuclear Power Plant. (NRC Inspection Report 99900404/90-21).


is greater than the maximum instantaneous
Westinghouse determined that most of its thermal-magnetic MCCBs with the


trip setting for circuit protection
nonadjustable instantaneous magnetic trip function could trip inadvertently.


recommended
Westinghouse attributed this behavior to interaction between the thermal


by the National Electric Code (NEC). Therefore, the NEC recommended
overload trip function and the instantaneous magnetic trip function under


level of protection
overload conditions. Under nonfault conditions, these functions may interact


may be insufficient
when the circuit current causes the thermal trip element to deflect until it


to prevent an unwanted trip. Proper application
presses on the MCCB's tripper bar at the same time that the instantaneous


of MCCBs depends strongly upon the use of accurate design assumptions.
magnetic armature is vibrating against the tripper bar. This interaction


Another application
causes the MCCB to trip.


problem involves the use of MCCBs equipped with both thermal overload trip elements and instantaneous
Westinghouse notified nuclear licensees of this problem and recommended that


magnetic trip elements.
they test these MCCBs in their intended circuits before releasing them for


A newly purchased
plant operation. Westinghouse also stated this recommendation on certificates


replacement
of conformance provided with its dedicated MCCBs sold as safety-related items.


Westinghouse
Potential interactions between thermal overload and instantaneous trip


===Type HFB3125 ambient compensating===
functions can be avoided by using a special class of MCCBs that are designed
MCCB tripped when a hydrogen skimmer fan motor at the Catawba Nuclear Station 7 9207020233
\J 1-IN 92-51 July 9, 1992 was started during testing after installation.


Duke Power Company personnel did not expect the MCCB to trip since the peak value of the ITC for the fan motor was thought to be well below the instantaneous
specifically for motor loads. These MCCBs include only instantaneous magnetic


trip band of that MCCB (NRC Inspection
trip functions for protecting against faults or short circuits. The trip


Report 99900404/90-01).
setpoints are normally adjustable and more accurate than those in thermal- magnetic MCCBs. These MCCBs, commonly referred to by the Westinghouse term


A similar Westinghouse
"motor circuit protectors," are intended for use in combination with motor


MCCB used as a turbine room sump pump breaker tripped in a similar manner at the Donald C. Cook Nuclear Power Plant. (NRC Inspection
contactors or starters. Thermal overload relays contained in the contactors


Report 99900404/90-21).
or starters provide the coordinated protection against overloads and fault


Westinghouse
currents which are below the magnitude necessary to actuate an instantaneous


determined
trip of the MCCB.


that most of its thermal-magnetic
Instances of premature tripping have occurred with MCCBs manufactured by ITE-
Siemens Company. The Carolina Power and Light Company, licensee for the


MCCBs with the nonadjustable
Shearon Harris Nuclear Power Plant, found that some of the 480 volt MCCBs


instantaneous
manufactured by ITE-Siemens, and purchased as commercial-grade, tripped


magnetic trip function could trip inadvertently.
prematurely when tested (NRC Inspection Report 99901177/90-01). The licensee


Westinghouse
had purchased these MCCBs as replacements for some older 600 volt ITE-Siemens


attributed
MCCBs. The ITE-Siemens Company tested the 480 volt MCCBs and found that these


this behavior to interaction
trips were initiated by the MCCBs' instantaneous magnetic trip function, when


between the thermal overload trip function and the instantaneous
induction motor loads were started. The manufacturer tested the older 600
volt MCCBs and found no premature trips. Rather, the older 600 volt MCCBs


magnetic trip function under overload conditions.
tripped at currents significantly above the levels at which an instantaneous


Under nonfault conditions, these functions
trip should have occurred.


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
i X -X


magnetic armature is vibrating
IN 92-51 July 9, 1992 The licensee's testing of the 480 volt MCCBs was judicious. ITE-Siemens


against the tripper bar. This interaction
stated that the instantaneous trip setpoints of commercial grade MCCBs-with


causes the MCCB to trip.Westinghouse
nonadjustable magnetic trips are not normally-verified at the factory.


notified nuclear licensees
However, ITE-Siemens and possibly other manufacturers of MCCBs will, upon


of this problem and recommended
request, verify that the instantaneous magnetic trip points of their


that they test these MCCBs in their intended circuits before releasing
commercial grade MCCBs with nonadjustable magnetic trips supplied to nuclear


them for plant operation.
utilities fall within the appropriate design band. Nevertheless, field


Westinghouse
testing of other MCCBs may be needed to verify that their magnetic trip points


also stated this recommendation
occur within the-design band (but not below the band) because other


on certificates
manufacturers may not routinely provide this verification for commercial grade


of conformance
MCCBs. For this type of MCCB, most manufacturers check only that the MCCB


provided with its dedicated
will trip instantaneously, without determining the current level at which the


MCCBs sold as safety-related
trip occurs.


items.Potential
Discussion


interactions
An MCCB can render safety-related equipment inoperable if it trips


between thermal overload and instantaneous
prematurely. Premature trips can result if the incorrect MCCB is selected


trip functions
(and/or incorrectly adjusted) as a result of inadequate analysis of the load


can be avoided by using a special class of MCCBs that are designed specifically
circuit including dynamic analysis of expected transients when determining


for motor loads. These MCCBs include only instantaneous
ratings, settings and coordination requirements. Premature trips can also- occur with properly applied and set MCCBs that are operating out of tolerance


magnetic trip functions
when incorrect bench testing methods and/or inadequate post-installation


for protecting
testing fail to detect the out of tolerance performance.


against faults or short circuits.
Acceptable testing methods and specifications are provided in some MCCB


The trip setpoints
manufacturers' technical publications. Industry and professional


are normally adjustable
organizations also provide guidance on MCCB testing methods, including generic


and more accurate than those in thermal-magnetic MCCBs. These MCCBs, commonly referred to by the Westinghouse
acceptance criteria, in documents such as the National Electrical


term"motor circuit protectors," are intended for use in combination
Manufacturers Association (NEMA) Standard AB4-1991, "Guidelines for the


with motor contactors
Inspection and Preventive Maintenance of Molded Case Circuit Breakers Used in


or starters.
Commercial and Industrial Applications." It should be noted that the


Thermal overload relays contained
application of generic field test tolerances to the instantaneous trip band on


in the contactors
manufacturers' time-current characteristic curves may not always ensure that


or starters provide the coordinated
the MCCBs meet plant-specific breaker coordination, circuit protection or


protection
technical specification requirements.


against overloads
Testing of properly applied and set MCCBs in accordance with industry


and fault currents which are below the magnitude
recommended practices should provide reasonable assurance that the MCCBs'
        instantaneous trip performance is acceptable for safety-related applications.


necessary
IN 92-51 July 9, 1992 This information notice requires no specific action or written


to actuate an instantaneous
response. If


trip of the MCCB.Instances
you have any questions about the information in this notice, please


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


tripping have occurred with MCCBs manufactured
Nuclear Reactor Regulation (NRR) project manager.                      of


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
ssi,D ide or


by ITE-Siemens, and purchased
Division of Operational Events Assessment


as commercial-grade, tripped prematurely
Office of Nuclear Reactor Regulation


when tested (NRC Inspection
Technical contacts:  Satish K. Aggarwal, RES


Report 99901177/90-01).
(301) 492-3829 Stephen D. Alexander, NRR


The licensee had purchased
(301) 504-2995 Nick Fields, NRR


these MCCBs as replacements
(301) 504-1173 Attachment:  List of Recently Issued NRC Information Notices


for some older 600 volt ITE-Siemens
.1  -
                                                              <-'Attachment


MCCBs. The ITE-Siemens
IN 92-51 July 9, 1992 LIST OF RECENTLY ISSUED


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


by the MCCBs' instantaneous
Information                                    Date of


magnetic trip function, when induction
Notice No.              Subject                Issuance      Issued to


motor loads were started. The manufacturer
92-50          Cracking of Valves in          07/02/92      All holders of OLs or CPs


tested the older 600 volt MCCBs and found no premature
the Condensate Return                        for BWRs.


trips. Rather, the older 600 volt MCCBs tripped at currents significantly
Lines of A BWR Emer- gency Condenser System


above the levels at which an instantaneous
92-49          Recent Loss or Severe          07/02/92      All holders of OLs or CPs


trip should have occurred.
Degradation of Service                        for nuclear power reactors.


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


testing of the 480 volt MCCBs was judicious.
92-48            Failure of Exide Batteries    07/02/92      All holders of OLs or CPs


ITE-Siemens
for nuclear power reactors.


stated that the instantaneous
92-47           


trip setpoints
==Intent==
ional Bypassing          06/29/92      All holders of OLs or CPs


of commercial
of Automatic Actuation                        for nuclear power reactors.


grade MCCBs-with
of Plant Protective


nonadjustable
Features


magnetic trips are not normally-verified
92-46          Thermo-Lag Fire Barrier        06/23/92      All holders of OLs or CPs


at the factory.However, ITE-Siemens
Material Special Review                      for nuclear power reactors.


and possibly other manufacturers
Team Final Report Findings, Current Fire Endurance


of MCCBs will, upon request, verify that the instantaneous
Tests, and Ampacity Cal- culation Errors


magnetic trip points of their commercial
92-45          Incorrect Relay Used in        06/22/92      All holders of OLs or CPs


grade MCCBs with nonadjustable
Emergency Diesel Generator                    for nuclear power reactors.


magnetic trips supplied to nuclear utilities
Output Breaker Control


fall within the appropriate
Circuitry


design band. Nevertheless, field testing of other MCCBs may be needed to verify that their magnetic trip points occur within the-design
92-44          Problems with Westing-          06/18/92      All holders of OLs or CPs


band (but not below the band) because other manufacturers
house DS-206 and DSL-206                      for nuclear power reactors.


may not routinely
Type Circuit Breakers


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


for commercial
olic Armature Carriers                        for nuclear power reactors.


grade MCCBs. For this type of MCCB, most manufacturers
Found on Elmwood Con- tactors


check only that the MCCB will trip instantaneously, without determining
92-42            Fraudulent Bolts in            06/01/92      All holders of OLs or CPs


the current level at which the trip occurs.Discussion
Seismically Designed                          for nuclear power reactors.


An MCCB can render safety-related
Walls


equipment
OL = Operating License


inoperable
CP = Construction Permit


if it trips prematurely.
IN 92-51 July 9, 1992 This information notice requires no specific action or written response. If


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


trips can result if the incorrect
one of the technical contacts listed below or the appropriate Office of


MCCB is selected (and/or incorrectly
Nuclear Reactor Regulation (NRR) project manager.


adjusted)
Original Signed by
as a result of inadequate


analysis of the load circuit including
Charles E. Rossi


dynamic analysis of expected transients
Charles E. Rossi, Director


when determining
Division of Operational Events Assessment


ratings, settings and coordination
requirements.
Premature
trips can also-occur with properly applied and set MCCBs that are operating
out of tolerance when incorrect
bench testing methods and/or inadequate
post-installation
testing fail to detect the out of tolerance
performance.
Acceptable
testing methods and specifications
are provided in some MCCB manufacturers'
technical
publications.
===Industry and professional===
organizations
also provide guidance on MCCB testing methods, including
generic acceptance
criteria, in documents
such as the National Electrical
Manufacturers
Association (NEMA) Standard AB4-1991, "Guidelines
for the Inspection
and Preventive
Maintenance
of Molded Case Circuit Breakers Used in Commercial
and Industrial
Applications." It should be noted that the application
of generic field test tolerances
to the instantaneous
trip band on manufacturers'
time-current
characteristic
curves may not always ensure that the MCCBs meet plant-specific
breaker coordination, circuit protection
or technical
specification
requirements.
Testing of properly applied and set MCCBs in accordance
with industry recommended
practices
should provide reasonable
assurance
that the MCCBs'instantaneous
trip performance
is acceptable
for safety-related
applications.
IN 92-51 July 9, 1992 This information
notice requires no specific action or written response.
If you have any questions
about the information
in this notice, please contact one of the technical
contacts listed below or the appropriate
Office of Nuclear Reactor Regulation (NRR) project manager.ssi,D ide or Division of Operational
===Events Assessment===
Office of Nuclear Reactor Regulation
Office of Nuclear Reactor Regulation


Technical
Technical contacts:   Satish K. Aggarwal, RES
 
contacts:  
Satish K. Aggarwal, RES (301) 492-3829 Stephen D. Alexander, NRR (301) 504-2995 Nick Fields, NRR (301) 504-1173 Attachment:
List of Recently Issued NRC Information
 
Notices
 
.-1<-'Attachment
 
IN 92-51 July 9, 1992 LIST OF RECENTLY ISSUED NRC INFORMATION
 
NOTICES Information
 
Date of Notice No. Subject Issuance Issued to 92-50 92-49 92-48 92-47 92-46 92-45 92-44 92-43 92-42 Cracking of Valves in the Condensate
 
Return Lines of A BWR Emer-gency Condenser


System Recent Loss or Severe Degradation
(301) 492-3829 Stephen D. Alexander, NRR


of Service Water Systems Failure of Exide Batteries
(301) 504-2995 Nick Fields, NRR


==Intent==
(301) 504-1173 Attachment:  List of Recently Issued NRC Information Notices
ional


Bypassing of Automatic
Brian K. Grimes, Director, Division of Reactor Inspection and Safeguards


===Actuation of Plant Protective===
and Ashok C. Thadani, Director, Division of Systems Technology concurred in a
Features Thermo-Lag


Fire Barrier Material Special Review Team Final Report Findings, Current Fire Endurance Tests, and Ampacity Cal-culation Errors Incorrect
previous version of this information notice. Notice was significantly revised


Relay Used in Emergency
to remove "regulatory guide" portions of original draft after above


Diesel Generator Output Breaker Control Circuitry Problems with Westing-house DS-206 and DSL-206 Type Circuit Breakers Defective
concurrences were obtained. I determined it was unnecessary to have re- concurrence at the Division Director level. C. E. Rossi


Molded Phen-olic Armature Carriers Found on Elmwood Con-tactors Fraudulent
*SEE PREVIOUS CONCURRENCE


Bolts in Seismically
OEAB:DOEA:NRR        SC/OEAB:DOEA:NRR            RPB:ADM      C/OEAB:DOEA:NRR


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


License CP = Construction
SKAggarwal*          MVagins*                    LCShao*      SAlexander*
06/08/92            06/08/92                    06/08/92      06/30/92 SELB:NRR            C/OGCB:DOEA:NRR            7W ssi


Permit
ASGill*              CHBerlinger*
06/29/92            06/10/92 Document Name:  92-51.IN


IN 92-51 July 9, 1992 This information
IN 92-XX


notice requires no specific action or written response.
June xx, 1992 This information notice requires no specific action or written response. If


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


about the information
one of the technical contacts listed below or the appropriate Office of


in this notice, please contact one of the technical
Nuclear Reactor Regulation (NRR) project manager.


contacts listed below or the appropriate
Charles E. Rossi, Director


Office of Nuclear Reactor Regulation (NRR) project manager.Original Signed by Charles E. Rossi Charles E. Rossi, Director Division of Operational
Division of Operational Events Assessment


===Events Assessment===
Office of Nuclear Reactor Regulation
Office of Nuclear Reactor Regulation


Technical
Technical contacts:   Satish K. Aggarwal, RES
 
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
(301) 492-3829 Stephen D. Alexander, NRR


notice. Notice was significantly
(301) 504-2995 Nick Fields, NRR


revised to remove "regulatory
(301) 504-1173 Attachment:  List of Recently Issued NRC Information Notices


guide" portions of original draft after above concurrences
Brian K. Grimes, Director, Division of Reactor Inspection and Safeguards


were obtained.
and Ashok C. Thadani, Director, Division of Systems Technology concurred in a


I determined
previous version of this information notice. Notice was significantly revised


it was unnecessary
to remove "regulatory guide" portions of original draft after above              %y


to have re-concurrence
concurrences were obtained. C. E. Ros i;2r                  B        a


at the Division Director level. C. E. Rossi*SEE PREVIOUS CONCURRENCE
*SE        PREVIOUS          CONCURe          RN-
*SEE PREVIOUS CONCURRENCE


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


NFields*05/21/92 EMEB:DE:RES
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*
SKAggarwal*         MVagins*                   LCShao*        SAlexander
06/08/92 SELB:NRR ASGill*06/29/92 SC/OEAB:DOEA:NRR


DFischer*05/22/92 C/EMEB:DE:RES
06/08/92             06/08/92                  06/08/92      06 / 0/92 SELB:NRR            C/OGCB:DOEA:NRR      D/DOEA:NRR


MVagins*06/08/92 C/OGCB:DOEA:NRR
ASGill*             CHBerlinger*          CERossi


CHBerlinger*
06/29/92             06/10/92               / /92 Document Name:  C:\CIRBRK      (ATB)
06/10/92 RPB:ADM TechEd*05/22/92 D/DE:RES LCShao*06/08/92 7W ssi C/OEAB:DOEA:NRR


AChaffee*06/04/92 RVIB:NRR SAlexander*
I I
06/30/92 Document Name: 92-51.IN


IN 92-XX June xx, 1992 This information
IN 92-XX


notice requires no specific action or written response.
May xx, 1992 This information notice requires no specific action or written response. If


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


about the information
one of the technical contacts listed below or the appropriate Office of


in this notice, please contact one of the technical
Nuclear Reactor Regulation (NRR) project manager.


contacts listed below or the appropriate
Charles E. Rossi, Director


Office of Nuclear Reactor Regulation (NRR) project manager.Charles E. Rossi, Director Division of Operational
Division of Operational Events Assessment


===Events Assessment===
Office of Nuclear Reactor Regulation
Office of Nuclear Reactor Regulation


Technical
Technical contacts:   Satish K. Aggarwal, RES
 
contacts: Satish K. Aggarwal, RES (301) 492-3829 Stephen D. Alexander, NRR (301) 504-2995 Nick Fields, NRR (301) 504-1173 Attachment:
List of Recently Issued NRC Information
 
Notices Brian K. Grimes, Director, Division of Reactor Inspection
 
and Safeguards
 
and Ashok C. Thadani, Director, Division of Systems Technology
 
concurred
 
in a previous version of this information
 
notice. Notice was significantly
 
revised to remove "regulatory
 
guide" portions of original draft after above %y concurrences
 
were obtained.
 
C. E. Ros i;2r B a*SE PREVIOUS CONCURe RN-*SEE PREVIOUS CONCURRENCE
 
OEAB:DOEA:NRR
 
NFields*05/21/92 EMEB:DE:RES
 
SKAggarwal*
06/08/92 SC/OEAB:DOEA:NRR
 
DFischer*05/22/92 C/EMEB:DE:RES
 
MVagins*06/08/92 RPB:ADM TechEd*05/22/92 D/DE:RES LCShao*06/08/92 C/OEAB:DOEA:NRR
 
AChaffee*06/04/92 RVIB:NRRA SAlexander
 
06 / 0/92 SELB:NRR ASGill*06/29/92 C/OGCB:DOEA:NRR
 
CHBerlinger*
06/10/92 D/DOEA:NRR
 
CERossi/ /92 Document Name: C:\CIRBRK (ATB)
I I IN 92-XX May xx, 1992 This information
 
notice requires no specific action or written response.
 
If you have any questions
 
about the information
 
in this notice, please contact one of the technical


contacts listed below or the appropriate
(301) 492-3829 Stephen D. Alexander, NRR


Office of Nuclear Reactor Regulation (NRR) project manager.Charles E. Rossi, Director Division of Operational
(301) 504-2995
 
                          --Am itpa 1 -G-i-l1        NR
===Events Assessment===
Office of Nuclear Reactor Regulation


Technical
(301t=043-i


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


Nick Fields, NRR (301) 504-1173 Attachment:  
(301) 504-1173 Attachment:   List of Recently Issued NRC Information Notices
List of Recently Issued NRC Information


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


and Safeguards
and Ashok C. Thadani, Director, Division of Systems Technology concurred in a


and Ashok C. Thadani, Director, Division of Systems Technology
previousversion of this informa ion noiVt            > 4 A/ N.


concurred
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in a previousversion
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                                                                      SAlexander    ASGill


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06/ /92 C,- A B r-t" -RPB:ADM C/OEAB:DOEA:NRR
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G/ Io192              / /92 Document Name:  C:\CIRBRK          (ATB)


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I r -. '
I r -.'K-'IN 92-XX May xx, 1992 This information
                              K-'
                                                                      IN 92-XX


notice requires no specific action or written response.
May xx, 1992 This information notice requires no specific action or written response. If


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


about the information
one of the technical contacts listed below or the appropriate Office of


in this notice, please contact one of the technical
Nuclear Reactor Regulation (NRR) project manager.


contacts listed below or the appropriate
Charles E. Rossi, Director


Office of Nuclear Reactor Regulation (NRR) project manager.Charles E. Rossi, Director Division of Operational
Division of Operational Events Assessment


===Events Assessment===
Office of Nuclear Reactor Regulation
Office of Nuclear Reactor Regulation


Technical
Technical contacts:  Satish K. Aggarwal, RES


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:
(301) 492-3829 Stephen D. Alexander, NRR
List of Recently Issued NRC Information


Notices Document Name: OEAB:DOEA:.
(301) 504-2995 N    raS.m l  G1J4INRK


RR NFieldsfJ Y5/h4/92 EMEB:DE:RES
Nick Fields, NRR


SKAggarwal
(301) 504-1173 Attachment:  List of Recently Issued NRC Information Notices


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SKAggarwal          MVagins                  LCShao         BKGrimes


AChaffee G/ 5/92 D/DRIS:NRR
/ /92                 / /92                    / /92          / /92 D/DST:NRR            C/OGCB:DOEA:NRR          D/DOEA:NRR


BKGrimes/ /92 D/DOEA:NRR
ACThadani            CHBerlinger              CERossi


CERossi/ /92}}
/ /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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