Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
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January 8, 1992
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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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