Page 44 - Nuclear Plant Journal - March April 2013
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Nuclear Plant Journal, March-April 2013
procedures, bills of material, etc., and
in the absence of a cost difference, it
seemed that refurbishment was the easier
path. But when Hope Creek considered
that the Masterpact breakers would not
need any refurbishment for forty years,
the cost-benefit equation shifted in favor
of replacement breakers.
In 2003, Greg and Dave began
presenting the business case for
replacement Masterpact breakers to
PSEG management, and after receiving
approval, a capital project was launched
in 2004 to replace more than 260 legacy
breakers – roughly 200 AC and 60 DC.
Breaker replacement began in October of
2004 during a refueling outage.
Breaker replacements continued for
the next six years, both online and during
outages, with the last legacy breaker
being replaced in January 2011. The final
Hope Creek Masterpact population is 266
(including installed spares), of which 242
were installed on energized switchgear.
Only 24 installations required the
switchgear to be deenergized. Six of these
24were 3,200Amp retro-fill replacements
which required switchgear modifications
to receive the permanently installed
cradle assemblies. The remaining 18
breakers requiring the switchgear to be
deenergized involved the installation of
a Neutral Current Transformer (NCT) on
the switchgear neutral bus. For reasons of
personnel safety, Hope Creek decided to
deenergize the bus for these installations.
Operating Experience
Anytime something new is tried,
there is a learning curve. Sometimes
we discover actual problems that were
not anticipated in the initial design and
sometimes we’re presented with systemic
problems and our natural bias is to blame
the new equipment, which hinders the
troubleshooting process. The following
are some examples of issues experienced
by Hope Creek as well as the resolutions.
During the initial installations
in 2004, Hope Creek experienced an
Advanced Protection (AP) trip on one
of the new AC Masterpact breakers. The
breaker was returned to NLI for failure
analysis. It was quickly determined that
a filter capacitor was required within the
trip unit. A Part 21 notification was issued
and the filter capacitor was installed into
all the newly manufactured trip units.
Hope Creek has since replaced all of the
installed trip units to the newer design.
In December of 2008, Hope Creek
again experienced an AP trip on one of
eight fan breakers that typically cycle two
or three times per day. The breaker was
sent to NLI for failure analysis where it
was concluded that there was excessive
tolerance within the Performance and
Sensor plugs that electrically connect
the trip unit to the breaker. This caused
a false signal as the breaker experienced
the in-rush current during the motor start.
It should be noted that nuclear plants are
fairly unique in their use of low voltage
breakers to directly start motors and other
large loads. The Performance and Sensor
plugs were enhanced by the manufacturer
and since then Hope Creek has replaced
all of the old style plugs on breakers used
as motor starters. The remaining plugs
will be replaced as part of the first six-
year PM cycle.
Similar to the previous situation,
Hope Creek also experienced scenarios
where fan breakers failed to close when
given an electrical signal. Based on the
symptoms, it was initially concluded that
the Masterpact and cradle assemblies
were to blame. But after multiple failures
and subsequent breaker replacements over
a two-year period, the focus shifted to a
remotely located control relay. The mean
time between failures for this application
had gotten down to four weeks. A failure
analysis performed by an independent test
lab on the control relay concluded that
heavy pitting on the contacts could have
caused an intermittent high-resistance
condition capable of preventing the close
coil from energizing. The last failure
was in August, 2012 and no failures have
occurred since replacing the control relay
in September, 2012.
Conclusion
Prior to replacing the breakers, Hope
Creek typically spent between ten and
twelve hours per breaker performing
preventative maintenance (inspection
and testing) on the legacy breakers.
The maintenance cycle was every four
years for critical and every six years for
non-critical breakers. Hope Creek now
performs preventative maintenance on a
six-year cycle and each breaker inspection
only requires four to five hours. Given
that approximately three-quarters of
Hope Creek’s breakers are classified as
critical, this is roughly a seventy percent
reduction in breaker maintenance time.
This is separate from eliminating the
need for overhauls.
Hope Creek was the first nuclear
plant to perform a complete replacement
of all legacy breakers with Masterpacts
and cradle assemblies. Today, there are
nearly 2,500Masterpact breakers installed
at twenty nuclear plants. Given that the
high cost to overhaul legacy breakers is
approximately the same as a replacement
breaker and cradle assembly, most sites
choose to replace breakers according to
their existing overhaul schedule. The
money that would have been used to
overhaul breakers now installs new
breakers that require less maintenance.
Masterpact breakers require no
overhauls for forty years or 10,000 cycles,
which essentially means never for most of
today’s operating nuclear plants. Legacy
breakers are very maintenance intensive
and so the battle being waged at many
sites is a maintenance battle. Rather
than attempting to optimize or perfect
the maintenance methods, perhaps the
solution is to eliminate the need for it.
The greatest victory is that which requires
no battle.
Contact: Dave Davis, AZZ | NLI,
7410 Pebble Drive, Fort Worth, Texas;
telephone; (615) 717-5800, email:
Masterpact breakers installed in
Hope Creek switchgear.
Mastering Breaker...
