Power August 2023 - 16

FOCUS ON O&M
3. U.S. natural gas-fired power generation capacity by initial year of operation. Source: U.S.
Energy Information Administration
During an online presentation, Chris
Killian, global sales director for Generators
with GE Gas Power, part of GE Vernova,
offered a prediction on how F-class
units could be operated over the next
10 years to support the North American
grid. " The hours that [they] are going to
be used will go down as the renewables
on the grid increase, " he said. " We also
see the number of starts are going to
increase on these units. A lot of these
units may end up being peakers. They'll
be subject to more cyclic duty operation.
So, we'll see these units viable in this
time, but they may be operated differently
than we've seen in the past. "
Killian said GE found similar trends
when studying E-class machines and
when looking at grids in Europe and Asia.
" Overall, it appears that there's going to
be many units that are still serviceable
for years to come, " he said.
Ian Hughes, principal engineer for
Generator Reliability with GE Gas Power,
covered some generator lifecycle considerations
during the presentation. He said
while it is common for a stator to operate
25 to 30 years before requiring a rewind,
a rotor may need to be rewound after
15 to 20 years of operation. However,
increased cycling and load swings will affect
lifecycle performance. " The cycling
that we're seeing occurring is affecting
shorted turns, movements of insulation,
and some other failure modes, " he said.
The most common failure modes
include grounds and shorts, mis-operations,
failures of main terminal studs,
pole-to-pole and coil-to-coil connectors,
corona, insulation and bar armor damage
and degradation, high vibrations/thermal
sensitivity, insulation and amortisseur
16
migration, contamination, collateral damage,
pro-active, and other lesser known
modes. " The thing to understand is that
there are roughly 26 [failure modes] and
they affect all of the different fleets-
some fleets are more susceptible to certain
failure modes, such as the air-cooled
fleets are more susceptible to corona
at and gather that information to help
yourself and to help us go through what
risk levels that you have on your units. "
Outage planning is also important,
and here, owners and operators need
to be as proactive as possible. With
all the units that entered service in
the early 2000s coming due for major
maintenance at roughly the same time,
you can expect contractor schedules to
fill quickly. " We really predict that the
demands are going to increase rapidly
over the rest of this decade, which
means that there's going to be more
demands on field service needs, " said
Killian. " So, scheduling this work as
soon as you can is paramount. We're
looking at 18 to 24 months as being
the time that you really should put solid
plans together for your outages. "
Another thing companies should consider
is pre-purchasing capital parts.
While pre-purchasing is fairly common
for gas turbine parts, it's less common
for generator components. Killian suggested
pre-purchasing is something that
should be done more going forward for
things like stator bar kits and replacement
rotors, for example.
" Not all generators will need a rotor or
stator rewind. It depends on a lot of
different factors, including your own
commercial considerations. "
-Ian Hughes, principal engineer for
Generator Reliability with GE Gas Power
than the hydrogen-cooled machines, "
Hughes said. " Not all generators will
need a rotor or stator rewind. It depends
on a lot of different factors, including
your own commercial considerations. "
Said Killian, " Really the best thing you
can do is understand your fleet risk. You
want to know what units you have [that]
are at higher risk now, and what's going
to be at higher risk in the future. You're
going to want to use some of the standard
predictive tools that we have in our
industry-things like flux probe readings,
partial discharge analysis for the stators,
looking at the results of the standard
electrical tests, look at things like excitation
current changes, perhaps, do you
have vibration issues and are those vibrations
sensitive to increases and decreases
in output? These are the types of
things that you're going to want to look
www.powermag.com
Killian also suggested rotating exciters
could be difficult to source in some
cases. " Many of these machines are
approaching over 20 years [in operation]
and there are some of these assets that
are no longer available, " he said. " You're
going to want to either buy the new replacements
that we have or explore getting
this work done from some of our
third-party partners. "
The fact is you can never be " too prepared "
for an outage. With so many units
potentially hitting the major maintenance
window at the same time, advanced
planning is more important than ever.
Owners and operators can set a course
for success by evaluating their machines
now and monitoring risks regularly so
they aren't surprised in the future. ■
-Aaron Larson is POWER's
executive editor.
POWER | August 2023

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Power August 2023

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