United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-45: Problems in Protective Relay and Circuit Breaker Coordination

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                  July 7, 1988

                                   BREAKER COORDINATION


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to a potentially 
significant problem concerning the possible lack of protective relay and cir-
cuit breaker coordination.  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 do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances: 

(1)  Lack of Circuit Breaker and Protective Relay Coordination at McGuire 
     Units l and 2 
     On September 6, 1987, a reactor trip and turbine trip occurred at the 
     McGuire nuclear station.  These trips resulted directly from a lack of 
     proper circuit breaker coordination on the plant's onsite electrical 
     distribution system.  To facilitate component maintenance, the power 
     supply to an auxiliary power panel board was shifted to an alternate 
     source, a 600 V motor control center (MCC).  This MCC also provides power 
     to a compressor in the plant's instrument air system.  A ground fault 
     developed in the compressor's motor.  This fault not only caused the 
     compressor motor's feeder breaker to open but also caused the feeder 
     breaker to the 600 V MCC to open.  The interruption of power to the MCC 
     precipitated the loss of the panel board.  As a result, the turbine 
     control system closed the main turbine throttle, governor, and intercept 
     valves causing the reactor to trip on high pressurizer pressure.

(2)  Lack of Breaker and Protective Relay Coordination at Salem Units 1 & 2 
     In October 1987, in response to staff questions raised during a fire 
     protection audit, the licensee of Salem Units 1 and 2 determined that the 
     lack of circuit breaker coordination in the plant could compromise 

                                                                 IN 88-45
                                                                 July 7, 1988
                                                                 Page 2 of 3

     the protection for redundant equipment and/or associated circuits from 
     common mode failures.  As a result, the licensee voluntarily shut down 
     Unit 2 which was the only unit operating at the time.  The resolution of 
     this issue contributed significantly to the outage that lasted ap-
     proximately 7 weeks.  

(3)  Lack of Coordination of Ground Fault Protective Devices at Monticello

     In June 1986, the Monticello licensee installed electrical ground fault 
     detection devices on circuit breakers throughout the onsite electrical 
     distribution system.  The installation of these devices altered the 
     coordination between circuit breaker, motor control centers, and con-
     nected loads so that actuation of protective devices in the proper 
     sequence was no longer assured.  In June 1987, at least two operating 
     events involving the loss of a train of emergency core cooling resulted 
     from the lack of coordination between protective devices.  These problems 
     were caused by the June 1986 design change which had not adequately con-
     sidered coordination of the protective devices in conjunction with the 
     design modification. 

Coordination is the selection and/or setting of protective devices so as to 
sequentially isolate only that portion of the system where the abnormality 
occurs.  To achieve this isolation, it is necessary to set protective devices 
so that only the device nearest the fault opens and isolates the faulted 
circuit from the system.  It is obvious that such selectivity becomes more 
important with devices that are closer to the power source, as a greater 
portion of the system can be affected. 

Backup protective devices are set to operate at some predetermined time 
interval after the primary device fails to operate.  A backup device is able 
to withstand the fault conditions for a longer period than the primary device. 

If a primary device fails to clear a fault and the backup device must clear 
it, then the design of the protective system becomes suspect. 

To optimize the coordination of protective devices, good engineering practice 
requires that consideration be given to the following: 

     (1)  available maximum short circuit currents;
     (2)  time interval between the coordination curves; and
     (3)  load current.


Other plants may also have problems with relay and breaker coordination.  The 
staff relies on the exercise of good engineering practice by the designers of 
electrical power systems at nuclear power plants to provide for the proper 
functioning of protective devices.  Breaker coordination is a key fire pro-
tection feature if cables for redundant trains pass through a fire area.  NRC 
                                                                 IN 88-45
                                                                 July 7, 1988
                                                                 Page 3 of 3

Generic Letter (GL) 81-12, "Fire Protection Rule (45 FR 76602, November 19, 
1980)," dated February 20, 1981 required licensees to submit information with 
regard to the design description of modifications necessary to meet Section 
III.G.3 "Fire Protection of Safe Shutdown Capability," 10 CFR 50, Appendix R, 
"Fire Protection Program for Nuclear Power Facilities Operating Prior to 
January 1, 1979."  This letter set forth general guidelines for protection of 
safe shutdown capability from the fire-induced failure of associated circuits.
ANSI/IEEE Standard 242-1986, "IEEE Recommended Practices for Protection and 
Coordination of Industrial and Commercial Power Systems" provides detailed 
guidance on achieving proper co-ordination.  

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the 
technical contacts listed below or the Regional Administrator of the 
appropriate regional office. 

                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation 

Technical Contacts:  N. K. Trehan, NRR 
                     (301) 492-0807 

                     E. N. Fields, NRR
                     (301) 492-1173 

Attachment:  List of Recently Issued NRC Information Notices
                                                            IN 88-45 
                                                            July 7, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                            NRC INFORMATION NOTICES 

Information                                  Date of 
Notice No.

88-44          Mechanical Binding of         6/24/88        All holders of OLs
               Spring Release Device                        or CPs for nuclear
               in Westinghouse Type                         power reactors. 
               DS-416 Circuit Breakers 

88-43          Solenoid Valve Problems       6/23/88        All holders of OLs
                                                            or CPs for nuclear
                                                            power reactors. 

88-42          Circuit Breaker Failures      6/23/88        All holders of OLs
               Due to Loose Charging                        or CPs for nuclear
               Spring Motor Mounting Bolts                  power reactors. 

88-41          Physical Protection           6/22/88        All holders of OLs
               Weaknesses Identified                        or CPs for nuclear
               Through Regulatory Ef-                       power reactors. 
               fectiveness Reviews (RERs) 

88-40          Examiners' Handbook for       6/22/88        All holders of OLs
               Developing Operator                          or CPs for nuclear
               Licensing Examinations                       power reactors. 

88-39          LaSalle Unit 2 Loss of        6/15/88        All holders of OLs
               Recirculation Pumps With                     or CPs for BWRs. 
               Power Oscillation Event 

88-38          Failure of Undervoltage       6/15/88        All holders of OLs
               Trip Attachment on General                   or CPs for nuclear
               Electric Circuit Breakers                    power reactors. 

88-37          Flow Blockage of Cooling      6/14/88        All holders of OLs
               Water to Safety System                       or CPs for nuclear
               Components                                   power reactors. 

88-36          Possible Sudden Loss of RCS   6/8/88         All holders of OLs
               Inventory During Low Coolant                 or CPs for PWRs. 
               Level Operation                              

88-35          Inadequate Licensee Performed 6/3/88         All holders of OLs
               Vendor Audits                                or CPs for nuclear
                                                            power reactors. 

OL = Operating License
CP = Construction Permit 

Page Last Reviewed/Updated Friday, May 22, 2015