Information Notice No. 88-58:Potential Problems with ASEA Brown Boveri ITE-51L Time-Overcurrent Relays

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

                                 August 8, 1988

                                   ITE-51L TIME-OVERCURRENT RELAYS 


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to potential 
problems involving ASEA Brown Boveri ITE-51L time-overcurrent relays.  It is 
expected that recipients will review this 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: 

Several spurious actuations of ASEA Brown Boveri (ABB) ITE-51L relays have 
occurred at the Beaver Valley nuclear power plant.  These actuations resulted 
in unnecessary interruptions of the electrical power supply to safety-related 
equipment.  The ITE-51L relays monitor circuit current.  When the magnitude of

the current exceeds a reference value for a specific duration, the relay 
actuates to energize the circuit breaker's trip coil.  The licensee has 
determined that the spurious relay actuations were caused by faulty silicon-
controlled rectifiers (SCRs) that were manufactured by the Motorola Company.  

SCRs are solid-state devices that are used as electronic switches in 
electrical circuits.  When a voltage is applied across the terminals of the 
SCR, the device is designed to allow current to flow only when "gated" or 
switched on by the proper electrical signal.  The SCRs that failed at Beaver 
Valley allowed current to flow in the absence of the proper gating signal.  
These "leakage" currents were of sufficient magnitude to energize the trip 
coil of the associated circuit breaker. 

The licensee was informed by Motorola that SCRs manufactured between the late 
1970s and early 1980s are susceptible to this mode of failure and that these 
SCRs are likely to fail within the first 2 years of service.  Since 1982, all 
SCRs manufactured by Motorola have been subjected to a "burn-in" test. In this

test, the SCRs are placed in a high-temperature environment both with and 
without voltage applied.  SCRs that pass this test are expected to perform 
normally for an extended period. 


                                                            IN 88-58 
                                                            August 8, 1988 
                                                            Page 2 of 2 

Beaver Valley Unit 2 has approximately 105 ITE-51L relays installed in safety-
related applications, and Unit 1 has 10.  The licensee is testing all the 
relays in Units 1 and 2 to determine whether the SCRs are faulty.  

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:  K. R. Naidu, NRR
                     (301) 492-0980 

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

Attachment:  List of Recently Issued NRC Information Notices

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