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Information Notice No. 92-05: Potential Coil Insulation Breakdown in ABB RXMH2 Relays
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 January 8, 1992 NRC INFORMATION NOTICE 92-05: POTENTIAL COIL INSULATION BREAKDOWN IN ABB RXMH2 RELAYS Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to a potentially safety-significant problem involving the coil insulation breakdown in Asea Brown Boveri (ABB) RXMH2 relays. 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 On August 12, 1991, United Controls Division of Hub, Incorporated, (United Controls) notified the NRC in accordance with Part 21 of Title 10 of the Code of Federal Regulations (10 CFR Part 21) concerning the failure of an ABB RXMH2 relay being used in the emergency diesel generator (EDG) bus load sequencing panels at the Florida Power & Light Company's Turkey Point Generating Station. The failed relay, one of approximately 300 ABB relays installed at Turkey Point, had failed to change state upon being energized during a preoperational test. United Controls purchased the relay from ABB as a commercial grade item and dedicated the relay for safety-related use as part of Turkey Point's EDG sequencing panels. On August 16, 1991, ABB also notified the NRC in accordance with 10 CFR Part 21 and provided further information concerning the failed relay. Discussion ABB conducted a failure analysis and found that the coil in the relay had suffered a short circuit of the windings at the point at which the beginning lead of the coil was crossed by the subsequent windings of each layer of wire as they were wound onto the coil spool. The beginning lead and the subsequent windings were to be separated by a piece of clear plastic adhesive tape placed over the beginning lead to hold it in a channel in the end flange of the coil spool. The separation tape would then hold the beginning lead in place and prevent abrasion from the subsequent windings during the winding process. However, upon examining the failed coil, ABB determined that during the winding 9201020171 . IN 92-05 January 8, 1992 Page 2 of 2 process, the tape had been pulled back and dislocated away from the beginning lead it was supposed to hold in the end flange channel of the coil spool. Some of the varnish insulation on the beginning lead was then apparently abraded during the winding process, allowing the insulation breakdown which caused the relay to fail. ABB inspected other relays, none of which had yet failed, to determine if the separation tape was adequately placed. The acceptance criterion established by ABB specified that the separation tape must cover the beginning lead with an overlap margin of 1.0 millimeter (mm) or greater. Although none of the relays had damaged or dislocated separation tape, ABB found that almost all of them had less than 1.0 mm of margin. United Controls and ABB determined that the problem had generic implications but that the scope was limited to relays with the particular coil design in question (type RXMH2, Models RK223068-EA and RK223069-EA) manufactured from March 1989 through September 1990. ABB identified the root cause of the problem as the performance of one factory employee who had manufactured relays within the date codes cited above. ABB has made a design change to reposition the separation tape on the end flange of the coil spool to more evenly cover the beginning lead and avoid conditions that could cause the separation tape to be dislocated during the winding process. ABB has also taken action to ensure that all pertinent draw-ings and procedures have been updated and corrected and that all affected employees have been trained on the changes. The manufacturer, ABB, did not believe that field data indicated a reliability problem with the type RXMH2 relay but recommended that in applications in which a failure to operate could cause a substantial safety hazard, the relays be checked for coil insulation integrity. The RXMH2 relays having the potential for insulation breakdown were manufac- tured from March 1989 to September 1990. The relays are marked in the upper right corner of the legend plate with the year and week of manufacture; the dates of concern indicated as 8909 up to, and including, 9036. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact the technical contact 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 contact: Bill Rogers, NRR (301) 504-2986 Attachments: 1. ABB 10 CFR Part 21 Notification to the NRC 2. List of Recently Issued NRC Information Notices .
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