IEEE Power & Energy Magazine - September/October 2020 - 46

costs. Despite this option having the highest capital cost, it
produced the lowest NPV by a significant margin and suggested that the intervention be completed in the first year to
take advantage of increased revenues for the longest period
of time.

Acaray I Turbine Components Analysis
In addition to the runner replacement, a full refurbishment
of all the turbine components was recommended, including
any upgrades or modifications required to accommodate
the new runner. Although the turbine components had been
adequately maintained, most components were beyond their
typical expected life and in need of refurbishment.

Acaray I Generator Components Analysis
An individual component analysis of the generator indicated
that refurbishment of most of the generator components
was recommended either immediately or within the next
five years. This included generator cooler replacement/
refurbishment, rotor pole winding refurbishment, rewinding of the stator, a new generator core, and an upgraded
excitation system. However, due to the recommendation to
increase the capacity of the runners, a completely new generator was recommended in lieu of refurbishing/replacing
the generator components.

table 7. The simulation results for Acaray I runners.
Option

NPV
Year of
Reduction (%) Intervention

Do nothing

Rehabilitation of unit with
identical runner (no increase
in capacity or efficiency)

Upgrade: replacement with
same capacity and higher
efficiency

176

Increase capacity: replacement
with higher capacity and
higher efficiency

297

table 8. The simulation results for Acaray II runners.

Option

NPV
Years Until Optimum
Reduction Intervention Timing
(%)
(From Simulation Date)

Do nothing

Rehabilitation of unit
4
with identical runner
(no increase in capacity
or efficiency)

Upgrade: replacement
with same capacity
and higher efficiency

ieee power & energy magazine

Acaray II Runner Analysis
The Acaray II runner analysis considered only two options:
✔ turbine rehabilitation
✔ replacement runner, same capacity, and higher efficiency.
The upgrade option assumes that the new runner will match
the capacity of the new generator, which had already been
purchased and was ready to be installed. All of the options
were compared against a do-nothing scenario (similar to the
Acaray I runner analysis). The percent reduction for each
option is presented in Table 8.
The results of the analysis indicated that the optimum
solution was to replace the runner within the next five
years. Although this remediation option had the highest
capital cost, the increased energy revenues, along with
lower risk and maintenance costs, resulted in the lowest
NPV. It is also noted that although runner replacement
previously took place in the early 2000s, the runners have
been experiencing cracks, high vibration, and cavitation
issues. Several modifications were made over the years
(e.g., replacing the wear ring with a higher gap) to reduce
vibration; however, both runners have experienced several
blade crack repairs. Although it is not typical to replace a
runner after this short of an operating history, the revenue
benefit, combined with reduced operating issues, resulted
in this recommendation.
Full refurbishment of the turbine components was suggested to take place at the same time as that of the runner
replacement. An analysis of the generators was excluded
from the study because their replacement had previously
been purchased, and the installation was planned for within
the next few years.

Overall CAPEX Plan for Existing Plants
All the major balance of the plant, in addition to the turbinegenerator equipment, was considered in the CAPEX plan.
Although the equipment had been well maintained over the
life of the facility, it was found that most components were
at or beyond their typical life. The baseline outputs from the
risk-based analysis of the asset management model indicated
that most components should be replaced immediately, suggesting that a large percentage of the CAPEX should take
place toward the start of the study horizon, with many similar components scheduled for rehabilitation or upgrade in
the same year.
To develop a feasible CAPEX plan that considers budgetary, labor, and unit outage constraints, the following requirements were applied to the prioritization/levelizing scheme of
the model:
✔ no more than one unit overhaul in any given year at
both plants
✔ no more than three spillway gate overhauls per year
per location
✔ no major overhauls before 2021 to allow for sufficient
engineering and procurement time
september/october 2020

IEEE Power & Energy Magazine - September/October 2020

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