Information Notice No. 90-43: Mechanical Interference with Thermal Trip Function in GE Molded-Case Circuit Breakers
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 29, 1990
Information Notice No. 90-43: MECHANICAL INTERFERENCE WITH THERMAL TRIP
FUNCTION IN GE MOLDED-CASE CIRCUIT
BREAKERS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is intended to alert addressees of a manufacturing
deviation in certain General Electric (GE) molded-case circuit breakers
(MCCBs) which may result in mechanical interference with the thermal
overcurrent trip function when internal accessory undervoltage release (UVR)
devices are installed. In addition, the information contained herein is
intended to emphasize the importance of conducting thorough pre-installation
testing to verify that plant components meet the functional performance
requirements of their safety-related applications. 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 do not constitute NRC
requirements; therefore, no specific action or written response is required.
Description of Circumstances:
In 1989, General Public Utilities-Nuclear (GPUN), the licensee for the
Oyster Creek Nuclear Power Plant (Oyster Creek), purchased 170 TED-type and
THED-type MCCBs from GE Nuclear Energy in San Jose, California. The MCCBs
were purchased as safety-related items and were supplied with GE Nuclear
Energy product quality certificates (PQCs). GE Nuclear Energy purchased the
MCCBs as commercial grade items (CGIs) from the GE Electrical Distribution
and Control Department in Plainville, Connecticut (GE-ED&C), who
manufactured the MCCBs at their Humacao, Puerto Rico, factory and installed
UVRs at their accessory installation facility in Mascot (Knoxville),
Tennessee. The MCCBs were dedicated by GE Nuclear Energy for use in
safety-related applications at Oyster Creek, in part, on the basis of
testing performed at the Puerto Rico factory.
In November 1989, one 15-ampere TED-type MCCB from this order was
bench-tested at Oyster Creek prior to installation. This MCCB had a UVR
installed in the standard location by phase "C" (right-hand side). The MCCB
failed to trip when 300-percent of rated current was applied to phase C of
the MCCB (a time-overcurrent test of the thermal trip function), whereas on
phases A and B,
9006250069
.
IN 90-43
June 29, 1990
Page 2 of 3
the thermal trips operated satisfactorily. The licensee returned the MCCB
to GE Nuclear Energy for failure and root cause analysis. The results of
the analysis have not yet been reported.
In May 1990, according to GPUN reports, Oyster Creek technicians
bench-tested seven more UVR-equipped MCCBs from the same order. Five of the
seven failed to pass the overcurrent trip test (also at 300 percent of rated
current) on phase C only. In addition, GPUN reported opening one of the
failed MCCBs, removing the UVR, and retesting the MCCB with satisfactory
results for the thermal overcurrent trip test on phase C. These
experimental results suggested that the UVR had been interfering with the
operation of the phase-C thermal overcurrent trip element because of its
close proximity to the phase-C element. However, it should be noted that
the UVR is not intended to act on the thermal element, but rather on the
common tripper bar that trips all three phases or poles.
Discussion:
On May 24, 1990, an NRC representative observed the GE ED&C testing of the
five GE TED-type MCCBs with UVRs installed (GE catalog number
TED136100UV4RS) which had failed pre-installation testing at Oyster Creek.
Inspection and testing revealed that the cause of the failure of the
overcurrent trip function was improper installation of the calibration screw
spring clips by the Puerto Rico factory, instead of improper installation of
the UVRs by the Knoxville facility, as previously believed by GE Nuclear
Energy. GE ED&C stated that the misoriented calibration screw spring clips
have no effect on the operability of the MCCBs unless internal UVRs are
installed. The Oyster Creek MCCBs passed the thermal overcurrent trip tests
at the GE Puerto Rico factory because the UVRs had not yet been installed.
After the UVRs were installed at the GE ED&C Knoxville facility, the
presence of the misoriented calibration screw spring clips caused mechanical
interference between the UVR and the thermal over-current trip function.
This was not detected at the GE ED&C Knoxville facility, because testing of
all MCCBs normal functions was not performed.
Deficiencies in manufacturing quality control and in the program for
dedication of CGIs for safety-related applications were exhibited by the
undetected misorientation of the calibration screw spring clips and the lack
of adequate retesting following installation of the UVRs. GE ED&C has
indicated that action will be taken, including design changes if necessary,
to prevent interference between the calibration screw spring clips and the
UVRs. In addition, GE ED&C has now instituted overcurrent trip testing of
MCCBs following the installation of UVRs at their Knoxville facility.
Although GE ED&C's failure analysis was demonstrated by testing, it has not
been firmly established that this condition is isolated to the MCCB shipment
in question. However, GE ED&C has stated that the problem is limited only
to the thermal overcurrent trip functions on phase C of their 3-pole,
E-frame MCCBs (types TED13XXXX and THED13XXXX), and only those equipped with
UVRs. This is a result of this model's unique, integral overcurrent trip
mechanisms and the proximity of the phase C thermal trip mechanism to the
tripping arm of an installed UVR.
.
IN 90-43
June 29, 1990
Page 3 of 3
Oyster Creek's routine pre-installation testing procedures detected and
prevented the use of the faulty MCCBs. Although the MCCBs were procured as
safety-related components through GE Nuclear Energy and were supplied with
the vendor's 10 CFR Part 50 Appendix B quality assurance certifications,
this testing was performed by the licensee in addition to the normal quality
assurance receipt inspection.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate NRR project
manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: K. R. Naidu, NRR
(301) 492-0980
S. D. Alexander, NRR
(301) 492-0995
Attachment: List of Recently Issued NRC Information Notices
.ENDEND
Page Last Reviewed/Updated Tuesday, March 09, 2021