POWER April 2016 - 74

GAS TURBINES
Rigorous Turbine Validation
Process Produces Sustained
Reliability Exceeding 99%
As technology capabilities and customer requirements have evolved, so have
gas turbine testing and validation methods. Mitsubishi Hitachi Power Systems
believes the proof of its long-term validation process is in its turbines'
reliability metrics.
Carlos Koeneke
W
hy would one want to validate a
turbine design? The answer is that
actual operation of new and more
advanced gas turbines can reveal issues that
are very difficult to predict on the drawing
board. As a result, the validation process
must focus on the detection of design deficiencies
that can be inadvertently introduced
when aiming for improved performance.
Gas turbine validation has improved considerably
in the past two decades. The previous
approach of testing at a " beta " facility
has evolved into a well-thought-out verification
process at the original equipment manufacturer's
(OEM's) facilities, and that has
reduced clients' exposure to prototypical
issues and the associated correction process.
Based on insurance community feedback,
more comprehensive validation has resulted
in a noticeable decrease in claims associated
with new and prototypical gas turbines.
From Shop Test to Plant Validation
Mitsubishi Hitachi Power Systems (MHPS)
started performing shop tests on its gas turbines
in the 1980s at Takasago Machinery
Works. MHPS's first step to verify turbine
behavior and detect design issues consisted
of running the gas turbine coupled to an electric
generator while using a water break to
dissipate the generated power. This approach
allowed detection of typical issues that might
occur during the first few hours of operation.
These include the tendency to experience
compressor surge, vibration, blade tip rubbing,
high cycle fatigue, and several potential
failure mechanisms that take place during
short-term operation.
Although this approach represented an
improvement to postponing verification of
a prototype until installation at a client site,
numerous failure mechanisms will not occur
until considerable operation time is accumulated.
Performing only a few hours of
validation essentially means that one is us74
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POWER
| April 2016
ing the client's site for long-term validation.
But long-term OEM validation can be very
expensive. The main roadblock to extending
validation at the OEM facility for longer
periods of time is the cost of fuel, as it can
surpass the cost of the gas turbine in just a
few months.
MHPS's solution to this financial constraint
was to construct commercial combined
cycle power plants with dispatching
contracts to the local utility. This concept
ensures operational expenses are covered
while the plants satisfy the clients' generation
requirements.
Figure 1 describes MHPS's approach to
the long-term validation cycle. This cycle
involves a continuous process wherein the
original design is developed in close interaction
with the research and development
(R&D) team. The new unit is manufactured
and operates commercially for long periods
at the MHPS combined cycle plant (T-Point),
where designs endure the rigors of commercially
dispatched units.
Detailed inspections are conducted, looking
for any signs to indicate an opportunity
for improvement. Enhanced designs are
developed-again in close cooperation with
R&D members' support-and installed back
into the unit to be exposed to the same rigorous
verification process. This cycle is repeated
for as long as it takes-until designers
and researchers are satisfied with the resulting
reliability.
MHPS's long-term validation approach
for a prototype is typically conducted for one
or two years before units are offered to potential
clients. Even after this time frame, the
T-Point unit remains in commercial operation
to fulfill the plant's contractual commitments
1. Mitsubishi Hitachi Power Systems' design and validation process.
Courtesy: MHPS
http://www.powermag.com
POWER April 2016

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