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Information Notice No. 88-58: Potential Problems with ASEA Brown Boveri ITE-51L Time-Overcurrent Relays
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 August 8, 1988 Information Notice No. 88-58: POTENTIAL PROBLEMS WITH ASEA BROWN BOVERI ITE-51L TIME-OVERCURRENT RELAYS Addressees: All holders of operating licenses or construction permits for nuclear power reactors. Purpose: 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. 8808020102 . 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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