without-project condition. A spare parts alternative

and the type of outage, the unit will either be

should also be considered where reasonable.

repaired or rehabilitated. If the unit is repaired, then

Incremental analysis of the alternatives should be

the probability of unsatisfactory performance in

performed to allow for optimization of the number

each successive time period continues to increase.

of components to be rehabilitated.

If a unit is rehabilitated, then the probability of

unsatisfactory performance is returned to a new

condition as the equipment is considered to be

physical condition of the individual components and

restored.

the potential sequencing of repairs.

consequences, in the form of cost resulting from

increased frequency of repair, increased mainte-

unsatisfactory performance with different probabili-

nance effort, and having to resort to more expensive

ties of occurrence. For example, in the Chapman

means of energy production (hydropower benefits

hydropower example, the first type could be consid-

calculations).

ered to be a catastrophic outage. For a generator

stator, this type of outage could occur if a signifi-

cant number of coils failed, and a rewind was the

only possible repair. The second type of outage is

less debilitating. This outage mode consists of a

repairable coil failure.

are needed to account for the engineering reliability

analysis. The engineering reliability analysis

mance, outage times and costs for repair are com-

establishes the probability of unsatisfactory per-

puted. For the Chapman generators, a repairable

formance for each component for current and future

coil failure may cause an outage of 1 month at an

conditions. This probability, over time, is inserted

estimated repair cost of ,000. For a catastrophic

for each year in the modeling sequence. Current

outage, the Chapman unit is estimated to be out of

conditions and probabilities of unsatisfactory

service for a period of 24 months at a repair cost of

performance vary for each individual turbine,

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,500,000.

generator, and transformer.

annual O&M costs are also estimated. Under exist-

generated for each component in a given time

ing conditions, the Chapman turbine units are

period. Based on the probability of unsatisfactory

dewatered, inspected, and repaired once every

performance in that time period, the unit either

6 months. If a unit is rehabilitated, inspections are

incurs an outage or continues to operate. For

assumed to decrease in frequency with a resulting

example, if the probability of unsatisfactory perfor-

reduction in O&M costs. The time associated with

mance for turbine unit number one in the year 1993

inspections and routine maintenance must also be

is 2.19 percent, then any random number generated

accounted for in each iteration.

between 0 and 1 that is less than 0.0219 will cause

an outage to occur; any number greater than 0.0219

will indicate that the unit is still available for opera-

all unit outages for a given year. Subroutines

tion. If the unit remains operational, then the

should be incorporated in the model to prevent

probability of unsatisfactory performance in the

double counting of outage time if two interrelated

next time period increases. A random number is

components are out concurrently. If the unit is

generated for each successive time period, and the

considered to be out of service in excess of

consequences are recorded. Should a unit incur an

12 months, outage times must be carried over into

outage, depending on the alternative being modeled

the next time period.

E-3

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