30 May 97
project level are often very small and can in many
now matches more closely the maximum capability
cases be supported under the Major Rehabilitation
of the turbines.
D-5. Duration Curve
d. Replacing runners and rewinding the gener-
ators will also improve the unit availability and
increase remaining service life. All of these benefits
To graphically display the amount of energy that
should be taken into consideration.
could be gained from a rehabilitation measure, a
generation-duration curve will be used. The curve
e. Replacing a Kaplan unit with an unreliable
could be developed using historical records or out-
blade adjustment mechanism can improve the unit's
put from a sequential streamflow routing model
response to changes in load and increase plant's
such as HEC-5.
a. Table D-1 shows the output of the plant by
unit, and Figure D-1 shows the annual generation-
duration curve for the example plant for the avail-
able period of streamflow record based on the
The easiest way to describe the benefit evaluation
existing condition of the plant. The duration curve
process is to walk through an example of a typical
in this case is based on weekly average streamflow
rehabilitation project. The proposed plan for the
data from a 60-year simulated operation study.
fictional "Chapman"project includes replacing all
Since this is a weekly average it does not reflect the
four worn turbine runners with new runners and
effect of peaking operation. This would require an
rewinding the generator stators (Appendix C).
hourly generation-duration curve, which would have
the same area under the curve but would show more
a. It will be assumed that when the original
operation at or near full output and less operation
runners were new, the units had an average overall
at low output levels.
efficiency of 87 percent, and tests have shown that,
b. However, for purposes of estimating energy
in their current condition, the overall efficiency has
dropped to 84 percent. With new runners, it is
output, a curve based on average daily, weekly, or
estimated that an average efficiency of 89 percent
monthly output should be used rather than an hourly
could be achieved. However, the rated capacity of
curve. The use of average values is necessary to
the turbines remains the same.
measure the amount of energy that would otherwise
be spilled if the rehabilitation measure were not
b. The rated capacity of the original generators
c. The horizontal line at the top of the duration
with state-of-the-art materials, the rated capacity of
curve defines the maximum capacity of the plant,