Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
ACCESSION #: 9511150360
ABB
November 7, 1995
Attention: Document Control Desk
The attached product defect notification was sent to our Nuclear
Distribution list on September 21, 1995. Although a copy was sent to the
NRC in Richland, WA at the Fast Flux Test Facility, it recently came to
my attention that the NRC in Washington, DC had not been copied at that
time. Enclosed please see that notification directed to your Document
Control Desk.
Signed,
Tina M. Rudolph
Quality Assurance Assistant
ABB Power T&D Company Inc.
Sanford, FL
ABB Power T & D Company Inc.
Distribution Systems Division Telephone: Telefax:
201 Hickman Drive 407 323-8220 407 322-8934
Sanford, FL 32771-8201 (Marketing/Engineering)
407 322-8938
(Operations)
407 328-9264
(Human Resources)
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ACCESSION #: 9511150368
ABB
November 7, 1995
Attention: Document Control Desk
Please se attached 10CFR50 Part 21 notification.
Point of contact is David E. Stone, Quality Assurance Manager, ABB Power
T&D Company Inc., Distribution Systems Division, Sanford, FL (407)
323-8220 ext. 159.
David E. Stone
ABB Power T & D Company Inc
Distribution Systems Division Telephone: Telefax:
201 Hickman Drive 407 323-8220 407 322-8934
Sanford, FL 32771-8201 (Marketing/Engineering)
407 322-8938
(Operations)
407 328-9264
(Human Resources)
ABB
RECORD OF EVALUATION
SUBJECT: 10CFR 21 Report of Product Defect - Stationary Secondary
Disconnect Conductor Strips for ITE 5HK Circuit Breaker Control at San
Onofre Nuclear Generating Station - Southern California Edison.
1.) Description of Deficiency:
A conductor strip making an electrical connection to a removable
circuit breaker element, broke and opened an indicating light
circuit during insertion (racking in) of the circuit breaker. The
failure was detected by a dark "breaker open" indicating light.
Investigation of the cause identified one conductor strip on the
secondary disconnect device which was broken at a 90 degree bend.
Two other strips on the secondary disconnect exhibited cracks at 90
degree bends. A test of the disconnect showed that one additional
contacts strip, with cracking at the bend, failed after the
equivalent of 32 racking cycles; but other testing of disconnects
with cracks in the conductor strips found no failures or crack
growth after the equivalent of 500 racking cycles. The strips are
components of a 12 conductor disconnect which automatically makes
and breaks contact between control components on the removable
circuit breaker and the stationary equipment. Conductor strip
material is cold-formed brass #2 (Half Hard) with silver plated
surface.
2.) Location and Date:
The failure was discovered by operating personnel at the San Onofre
Nuclear Generating Station - Southern California Edison in June
1995. The HK Switchgear was shipped in 1976.
3.) Analysis of Safety Implication:
San Onofre personnel conducted further onsite investigation and
prepared a comprehensive "Safety Engineering Root Cause Report"
which explores function of the disconnect, mitigation of risks and
corrective action planned for San Onofre - Attachment #1.
The broken conductor deficiency, in another location on the
disconnect, could have prevented trip or close of the circuit
breaker by electrical control. This would disrupt normal operations
and require manual trip or close at the circuit breaker location.
San Onofre personnel checked records for similar problems in the
past on their system and at nine other nuclear stations which use
5HK switchgear. One prior instance of disconnect conductor breakage
at San Onofre in 1990 and one possible instance at another plant
were found.
ABB has had no indication that this is a significant maintenance
problem. The HK switchgear design has been in production since the
early 60's, there are hundreds of thousands of these conductor
strips in commercial and nuclear services and only three known
failures have occurred. The material specification for these.
conductor strips was originally C.F.Brass #2; the specification was
changed in 1982 to add "Alloy C230". No cracking of conductor
material during forming has been noted with the C230 alloy material.
Functional testing to verify circuit breaker ability to close, trip,
recharge stored energy springs and provide accurate indication
verifies that nothing has disrupted the electrical connections to
the breaker during racking. This is a prudent measure to take after
racking HK breakers into "connected" position; assuring the operator
that the breaker will function electrically as long as it stays in
that position.
ABB
4.) Conclusions:
The flexure of the conductor strip during racking operations is the
cause of failure. The San Onofre Report asserts that seismic forces
will have no effect on the conductor strips of a fully engaged
breaker, ABB concurs.
There is evidence that pre-'82 disconnect conductor strips may be
C.F. Brass Alloy C260 and may exhibit cracks at the bends. There is
no method of judging the vulnerability of strips with visible
surface cracks, surface hardness is not a reliable indicator. It is
advisable, therefore, that a careful visual inspection of 5HK, 7.5HK
and 15HK secondary contacts on critical circuit breaker positions be
planned at a maintenance availability during which the switchgear
can be completely deenergized. Replacement of disconnects which
exhibit cracks in conductors is suggested. Attachment 3 lists HK
nuclear switchgear orders which are likely to have disconnects with
conductor strips subject to cracks.
Conductor strips which have surface cracks at bends will probably
never break but breakage during racking cannot be ruled out, based
on present data. If the strips have no obvious cracks at bends, no
action should be taken; there is no evidence that cracks develop in
service.
5.) Corrective Action:
The 1982 specification change, calling for Alloy C230, appears to
have eliminated the possibility that cracks occur during fabrication
of the conductor strips. Inspection of parts in stock provides
further assurance, see attachment 2 for test data.
6.) Reference Documents:
Attachment #1 - Root Cause Evaluation of 4KV Breaker Secondary
Contact Block Failure, RCE 95-010, Southern
California Edison. (Full Report-less
attachments)
Attachment #2 - ABB Material Analysis of currently stocked
secondary conductor strip samples.
Attachment #3 - HK switchgear which, may incorporate Alloy 260
conductor strips, with possible forming cracks,
into secondary disconnect assembly. assembly.
7.) Action to Prevent Recurrence:
Material change, see #5; ongoing parts inspection.
8.) Point of Contact:
David Stone, Quality Assurance Manager, (407) 323-8220, ext. 159.
9.) Prepared By:
This report prepared by David Stone.
10.) Reviewed By:
Aubrey Jackson - Total Quality Mgr. Norb Hagenhoff-VP/General Mgr.
ABB Power T&D Company Inc.
Distribution Systems Division
201 Hickman Drive
Sanford, FL 32771-8201 Telephone 407 323-8220
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