ETL 1110-2-550
30 May 97
Figure D-3. Energy gain, rewinding stators
that component reliability tends to decrease with
rewind could contribute to improved availability for
age. In addition, it is necessary to account for the
the plant. Replacing old, failure-prone components
length of the outage and the cost of repair. In order
with new components usually reduces the amount of
to account for all of these factors, event tree models
time generating units are out of service due to
have been developed for estimating the energy
forced outages. This in turn increases the amount
benefits attributable to reliability improvements.
of generation the plant can produce.
This topic is discussed in more detail in Appendix
E. However, for purposes of illustration, it is
c. Figure D-4 illustrates the concept of genera-
assumed that the combined gain in average annual
tion loss due to forced outages. The shaded area
energy benefits due to improvement in the
represents the generation that would be lost if
availability of the turbines and generators is
forced outages kept one unit out of service one-
0,000.
third of the time (high value assumed for illustrative
purposes only; forced outage rates for hydroelectric
D-9. Computation of Energy Benefits
plants are typically less than 10 percent). A reha-
bilitation measure which reduces the outage rate
The average annual gain in energy benefits that
would reduce the size of this area, thus increasing
accrues to a rehabilitation plan is computed by
energy output. The process of computing the loss
applying a unit energy value to the gain in energy
in energy due to outages is rather complex because
creditable to that plan. Assuming an energy value
it is necessary to account for the combined
of /MWh, the gain in energy benefits for the
probability characteristics of multiple components
runner replacement and generator rewind measures
(turbine runners and generator windings, for
would be as follows:
example), the combined probabilities of different
numbers of units being out of service, and the fact
D-5
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