Information Notice No. 87-42: Diesel Generator Fuse Contacts
SSINS No.: 6835
IN 87-42
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
September 4, 1987
Information Notice No. 87-42: DIESEL GENERATOR FUSE CONTACTS
Addressees:
All nuclear power reactor facilities holding an operating license or a con-
struction permit.
Purpose:
This information notice is being provided to alert recipients to potential
failures of emergency electrical power supplies resulting from misalignment
and/or degradation of fuse contacts. It is expected that recipients will
review the information for applicability to their facilities and consider
actions, if appropriate, to avoid similar problems. However, suggestions
contained in this notice do not constitute NRC requirements; therefore, no
specific action or written response is required.
Description of Circumstances:
At Browns Ferry Nuclear Plant, Unit 3, during routine surveillance testing of
an emergency diesel generator on April 20, 1987, an explosion occurred in the
electrical control cabinet. The explosion resulted from a phase-to-phase
short in a cable bundle in the potential transformer (PT) fuse compartment.
The electrical control cabinet was supplied by Power Systems Division of
General Motors, the diesel generator manufacturer. The licensee's investiga-
tion revealed that the cables routing power from the PT fuses to the trans-
formers shorted after their insulation failed because of an overtemperature
condition. This condition is believed to have been caused by an excessive air
gap and/or poor contact between the spring finger contact arrangement of the
PT fuses. The spring finger contacts were manufactured by Allis-Chalmers.
The moveable contacts are mounted to the PT fuse compartment door so that when
the door is opened, the contacts disconnect, thereby preventing anyone from
pulling the fuse while it is carrying current. When the door is closed, the
moveable contact finger connects with the stationary contact. Although the
contacts were destroyed by the event, the licensee concluded that an air gap
due to misalignment or contact degradation from corrosion, pitting, or
burning, caused arcing and eventual failure. Although the cause has been
attributed to inadequate maintenance of the contact, the licensee is
considering design changes as a permanent solution.
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. IN 87-42
September 4, 1987
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Discussion:
The licensee inspected the other seven diesel generator control cabinets and
found three other instances of poor contact. Visual inspection for burning,
pitting, corrosion and improper alignment and mating of contact surfaces were
performed as well as micro-ohmmeter checks. Since 1973, four previous onsite
events involving this type of pressure contact arrangement have occurred on
non-safety-related electrical boards designed by General Electric Co. Because
of this type of problem, General Electric modified similar contacts on its
electrical boards to knife switch contacts. The licensee considers the
problem to be generic and has initiated a visual inspection of all PT fuse
compartments.
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 Contacts: C. Brooks, RII
(205) 729-6196
Samuel D. MacKay, NRR
(301) 492-8394
Attachment: List of Recently Issued NRC Information Notices
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