ETL 1110-2-550
30 May 97
D-17. Total Gain in Benefits
d. Subtracting out the previously calculated
benefits for the gains in dependable capacity, the
gain in capacity benefits as a result of improved
The total annual power benefits attributable to the
reliability is 5,000 (0,000 - 475,000) for the
combined runner replacement/stator rewind plan
new runners alone, and 5,000 (,700,000 -
would be as follows:
3,895,000) for the combined plan of new runners
plus rewind.
Energy benefits
= ,430,000
Capacity benefits
= ,700,000
Total benefits
= ,130,000
D-15. Benefits from Increasing Remaining
Service Life
D-18. Last-Added Test
The hydroelectric power benefits accruing from
a. Standard economic practice requires that
replacing equipment before it fails are limited to the
differences in unit outage times. A planned
separable components of multi-component plans be
rehabilitation program will substantially reduce the
incrementally justified on a last-added basis. For
time that a unit is out of service when compared
instance, the example rehabilitation plan includes
with waiting for a major equipment failure.
two components. For the plan to be economically
feasible, both runner replacement and generator
rewind would have to be individually justified on a
D-16. Flexibility Benefits
last-added basis. This assures that the plan with the
highest net National Economic Development
a. An additional area where benefits might
benefits (i.e., benefits-costs) is identified, as called
accrue to power plant rehabilitation is in the area of
for in ER 1105-2-100.
flexibility--the ability of a power plant to come
b. Last-added analysis refers to a comparison
on-line quickly and to respond rapidly to changes in
load. An example might be a plant with aging
of the incremental benefits gained by one compo-
Kaplan units which have deteriorated to the point
nent of a plan on a last-added basis, with the incre-
where the turbine blade adjustment mechanism can
mental costs of including that component in the
no longer be operated reliably. In such cases, the
plan. The last-added benefits for a component are
blades may have to be welded in a fixed position so
determined by deducting the benefits of a plan with
that they lose their ability to follow load. Rehabili-
that component excluded from the benefits of the
tating the units would restore this capability, and
plan with all components included. Again referring
this in turn would generate some benefits which
to the example, the last-added benefits of the gener-
could be used to help support the investment in the
ator rewind would be the benefits of the total plan
rehabilitation work.
minus the benefits of runner replacement alone. A
similar process would be followed to determine the
b. Unfortunately, while it is widely agreed that
incremental benefits of the runner replacement.
flexibility benefits are an important hydroelectric
Once incremental benefits are determined, they are
project output, it is difficult to quantify such
compared to the incremental costs of including the
benefits. EPRI and others have done some work in
component. If the incremental benefits exceed the
this area, but so far an accepted procedure for
incremental costs, the component is justified on a
quantifying flexibility benefits does not exist.
last-added basis.
However, if a proposed rehabilitation project does
improve a project's flexibility, this should at least be
addressed qualitatively in the rehabilitation project
feasibility report.
D-9
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