Information Notice No. 92-03: Remote Trip Function Failures in General Electric F-Frame Molded-Case Circuit Breakers
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
January 6, 1992
NRC INFORMATION NOTICE 92-03: REMOTE TRIP FUNCTION FAILURES IN GENERAL
ELECTRIC F-FRAME MOLDED-CASE CIRCUIT
BREAKERS
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
resulting from the possible failure of the remote trip functions of General
Electric (GE) F-frame (225-ampere frame size) molded-case circuit breakers
(MCCBs). 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 November 5, 1991, GE Nuclear Energy (GE NE), San Jose, California, issued
an interim notification of its evaluation of a deviation in accordance with
the latest revision (effective October 29, 1991) of Part 21, "Reporting of
Defects and Noncompliance," of Title 10 of the Code of Federal Regulations
(10 CFR Part 21). The notification described the deviation as a "tolerance
buildup" in certain GE F-frame MCCBs with undervoltage releases (UVRs) and
shunt trip devices (STs) that may inhibit these internal accessory remote
trip devices from functioning properly under conditions that produce
sustained high internal temperatures in the MCCBs.
The attachment to the GE NE notification was taken from a draft Service
Advice Letter (SAL) on this subject being prepared by the MCCB manufacturer,
GE Electrical Distribution and Control (ED&C), in Plainville, Connecticut.
GE NE plans to send the 10 CFR Part 21 interim notification to all of its
customers who have purchased F-frame MCCBs for safety-related applications
and to all GE NE Material Services field representatives. GE ED&C plans to
send the SAL (issued November 25, 1991 as SAL 91-2F) to all of its customers
of record, many of whom are distributors. However, both the F-frame MCCBs
and their accessory trip devices are available on the open market as
commercial grade items through various distribution paths. Therefore, the
licensees for some nuclear plants who use these MCCBs may not receive the GE
notifications.
9112300071
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IN 92-03
January 6, 1992
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Discussion
Although still evaluating the problem, the MCCB manufacturer has determined
that assembly and operational variations caused the reported failures. The
variations reportedly resulted from (1) tolerances in mounting the accessory
trip devices in the MCCBs, (2) tolerances on the adjustment of the ambient
compensating bimetal (part of the thermal overload trip mechanism), and (3)
sustained high operating temperatures in the MCCBs. The high internal
temperature in the MCCB required to produce a condition conducive to the
malfunction can result from continuous high current load (greater than 50
percent of the overcurrent trip unit rating for more than 2 hours) together
with a high ambient temperature in the enclosure. A secondary heat source
could also produce the high temperatures required for this malfunction.
GE NE stated in its interim notification that UVR- and ST-equipped MCCBs
produced after April 1991 (date codes J116= and I116=) incorporated changes
that would prevent this condition. GE NE also stated that an MCCB may or
may not exhibit this malfunction, depending on the particular circumstances
associated with the assembly of the breaker and the accessory remote trip
devices, in conjunction with the high temperature service conditions
believed to be conducive to failure. Nevertheless, GE NE maintained that
affected MCCBs will trip under overcurrent conditions and will trip remotely
at the lower MCCB internal temperatures usually present with lower load
currents and enclosure ambient temperatures or without secondary heat
sources.
GE NE initially reported that it had identified a specific safety-related
application for the affected F-frame MCCBs equipped with internal accessory
remote trip devices. The identified application is associated with the
multiple electrical protection assemblies (EPAs) used in boiling water
reactor (BWR) plants to monitor power quality to the reactor protection
system (RPS). The EPAs trip the F-frame breakers for the RPS power supplies
by means of the remote trip devices if the EPAs detect overvoltage,
undervoltage, or underfrequency conditions in RPS power. In addition, GE NE
informed the NRC in a subsequent communication that it may also have
supplied some of the affected MCCBs as part of subassembly-level
applications not separately identified in GE NE records. The affected MCCBs
fitted with factory-installed remote trip accessories may also be used in
numerous other applications in all types of nuclear plants in which remote
tripping of an F-frame MCCB by means of the UVR or ST may be a
safety-related function.
The presence of UVRs or STs in F-frame MCCBs should be apparent when the
units are installed in the plant. However, even if accessory designation
markings are not evident, affected MCCBs can be recognized by the two UVR or
ST lead wires protruding through small openings in the sides of the MCCB
case. Additionally, UVRs set up for monitoring 240, 480, or 600 volts-AC or
250 volts-DC should have an external dropping resistor connected in series
with one of their lead wires. Attachment 1 lists the breaker frame type
designations of
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IN 92-03
January 6, 1992
Page 3 of 3
the potentially affected MCCBs and the catalog numbers of the affected
internal accessory remote trip devices and also gives the date codes of the
units believed by the manufacturer to be affected.
In view of the potentially wide scope of application of the affected MCCBs,
addressees may find the affected types of UVR- and ST-equipped MCCBs both
installed and in the warehouse. Addressees who find any affected MCCBs may
consult the manufacturer on this subject to determine the appropriate
corrective action, including testing for the existence of the malfunction,
analyzing the potential high temperature producing conditions, or replacing
the affected components.
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: S. D. Alexander, NRR
(301) 504-2995
Attachments:
1. Affected MCCBs and Accessories
2. List of Recently Issued NRC Information Notices
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Attachment 1
IN 92-03
January 6, 1992
Page 1 of 1
AFFECTED MCCBs and ACCESSORIES
The affected GE F-frame ("F-225 Line") MCCBs include the breaker types or
frames listed below which can be fitted with any of the accessory remote
trip devices with the listed catalog numbers:
BREAKER FRAMES SHUNT TRIPS UNDERVOLTAGE RELEASES
TFK, THFK TFKSTA12 TFKUVA1
TFJ TFKSTA13 TFKUVA2
THLC2 TFKSTA7 TFKUVA4
THLB2 TFKSTA8 TFKUVA6
THLC4 TFKSTA9 TFKUVA7
TLB4 TFKSTA11 TFKUVA8
TFKUVA9
TFKUVA10
TFKUVA11
According to GE NE and GE ED&C, the tolerance buildup affects F-frame MCCBs
and UVRs and STs assembled between August 1979 and April 1991 (accessory
date codes N927* through N116=). The potentially affected MCCBs could have
manufacturing date codes J927* through J116= (I116= for current limiting
frames), but ED&C reported no identifiable volume of field returns for this
condition among MCCBs built before the fourth quarter of 1987 (breaker date
codes J736+ and I736+). The accessory date code is its manufacturing date
code and only appears on the accessory itself. However, the date code from
the accessory installation facility may appear on the MCCB case in addition
to the manufacturing date code of the MCCB.
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