United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-41: Failures of Certain Brown Boveri Electric Circuit Breakers

                                                   SSINS No.:  6835
                                                      IN 87-41

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

                                 August 31, 1987

Information Notice No. 87-41:  FAILURES OF CERTAIN BROWN BOVERI
                                   ELECTRIC CIRCUIT BREAKERS


All nuclear power reactor facilities holding an operating license or a con-
struction permit. 


This information notice is provided to inform recipients of failures of 
certain Brown Boveri Electric (BBE) circuit breakers.  It is expected that 
recipients will review the information for applicability and consider actions, 
if appropriate, to preclude similar problems from occurring at their 
facilities.  Suggestions contained in this notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.  

Description of Circumstances:

Concerns regarding BBE circuit breakers have been recently reported to the 
NRC.  On April 20, 1987, Duquesne Light Company, the Beaver Valley Unit 2 
licensee, notified the NRC in accordance with the reporting requirements of 10 
CFR 50.55(e) of the failure of a BBE Type 5HK Class IE 4-KV circuit breaker.  
When the circuit breaker was racked onto the bus and 125-V DC control power 
was applied to the breaker's control circuit, the closing spring charged and 
the circuit breaker immediately closed and opened several times before the 
control power could be turned off.  The licensee determined by field testing 
that the closing coil was not being energized.

Another problem with BBE circuit breakers occurred at River Bend and was 
reported in Licensee Event Report (LER) 87-004, dated March 6, 1987.  On 
February 6, 1987, with the unit at full power, the Division I diesel generator 
4.16-KV output circuit breaker (Gould-Brown Boveri Type 5HK) failed to close 
during a weekly surveillance test.  The licensee's inspection of the output 
circuit breaker revealed that a mounting bolt had fallen out of the closing 
spring charging motor, rendering the motor inoperable.  Further investigation 
revealed several other circuit breakers that contained loose or missing charg-
ing motor mounting bolts.  The licensee also stated that the River Bend 
circuit breaker preventive maintenance program, which the licensee believes to 
be in accordance with the vendor's recommendations, did not detect this 
problem.  The licensee believes the root cause of the problem to be 
insufficient torquing of the charging motor mounting bolts by the vendor.  

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                                                            August 31, 1987
                                                            Page 2 of 2


With regard to the repeated closing and opening of the breaker, this problem 
was also reported to the NRC in accordance with the reporting requirements of 
10 CFR 50.55(e) by Philadelphia Electric Company, for Limerick Unit 1, in 
1983.  The circuit breakers involved were returned to BBE for analysis, and 
BBE transmitted its findings to the NRC in a letter dated April 20, 1983.  BBE 
stated that the repeated closing and opening of the circuit breaker can be 
corrected by the addition of a light spring to the close latch in the circuit 
breaker operating mechanism.  BBE also stated that, depending upon the year of 
manufacture, circuit breakers may or may not have been originally supplied 
with this spring.  BBE recommended that these springs be installed in circuit 
breakers that were not originally supplied with one.  This problem may also 
affect BBE Type 7.5HK, 15HK, and 38HK circuit breakers.  Although information 
regarding this problem has been distributed by BBE and the Institute for 
Nuclear Power Operations (INPO), the Beaver Valley event indicates that this 
problem still exists.  Licensees and applicants may wish to contact BBE to 
obtain additional information regarding this problem and appropriate 
corrective actions.

Failure of a circuit breaker to fully close on demand, inadvertent closure of 
a circuit breaker, or loose or missing closing spring charging motor mounting 
bolts could result in a circuit breaker not performing its intended function.  
This, in turn, could result in the loss of a power supply (such as a vital bus 
or a diesel generator).  

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

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

Technical Contact:  Jack Ramsey, NRR
                    (301) 492-9081

Attachment:  List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Friday, May 22, 2015