ETL 1110-2-550
30 May 97
6. Engineering Reliability Analysis
contacted on the requirements for justifying
relatively low cost items below the main
This section discusses the many facets of reliability
rehabilitation and major maintenance threshholds
of hydropower equipment in relatively broad terms.
and for using HYD-QUAD. HYD-QUAD is
Appendices B through E go into further detail by
discussed in Appendix F.
exploring a theoretical project and applying an
analysis to that project. The overall engineering
(2) Caution must be exercised when relying on
reliability analysis consists of four independent
maintenance costs as indicators of reliability
analyses to determine the following equipment
because they do not necessarily reflect equipment
reliability factors: (a) forced outage experience and
reliability. Explanations of costs and maintenance
maintenance costs; (b) efficiency and capacity;
efforts should be presented in the evaluation
(c) availability; and (d) dependability. The life-
reports. Maintenance and repair records should be
cycle costs of each segment are compiled for use in
tabulated and charted to show the trends over the
the economic analysis. Benefits for each alternative
past few years. Projections for future years can be
are calculated by subtracting the average annual
made using sound engineering judgment to
equivalent life-cycle costs for the alternative from
extrapolate these costs and should be made for each
the average annual equivalent life-cycle costs for the
of the alternatives being considered. Lost energy
base condition. The following paragraphs briefly
and capacity are discussed below under the topic of
summarize each segment of the reliability analysis.
availability.
a. Forced outage experience and maintenance
b. Efficiency and capacity. This portion of the
costs. A forced outage occurs when a power plant
reliability analysis can be applied to any piece of
component fails to perform satisfactorily and causes
equipment that has an effect on the ability of the
an interruption in power production. A planned
generating unit to produce rated power at rated
outage occurs when a unit is intentionally taken out
efficiency. However, this approach is primarily
of service to perform planned repairs, replacements,
applicable to the turbines, generators, and
routine inspections, and rehabilitations.
transformers. Turbines will be used as an example
in the following explanation.
(1) The life-cycle cost of equipment
maintenance and repair includes labor and material
(1) Part of the aging process of turbines is the
costs as well as lost energy and capacity benefits
development of cracks, corrosion, erosion, scaling,
associated with forced or planned outages.
and cavitation damage. Much of this damage is
Therefore, reliability is a determining factor in
corrected by welding, which induces material
estimating life-cycle costs. Decreased reliability
stresses and can change the shape of the turbine
may be represented by a large increase in labor and
water passage thereby lowering the efficiency of the
materials costs over time. Certainly, increasing
turbine. Thus, degradation of turbine performance
maintenance costs and unit outage hours can both
occurs as a result of the aging process and can be
be used to indicate a need for equipment
exacerbated by repairs which are necessary to keep
replacement or rehabilitation. Project records for
the turbine operational.
the equipment in question can be used to document
past trends and as a basis to make future
(2) The first step in quantifying the perfor-
projections. Currently, such documentation may be
mance degradation is to determine current and
the only justification required for replacing
original levels of performance. Current efficiency
relatively low cost items that are critical for power
and power output must be determined by field
production. In the near future, economic
testing at similar settings used in the original field
justification that incorporates reliability will be
tests. The current performance must then be
required. The economic justification will
compared with the original level of performance to
be conducted using the Hydropower QUADRANT
establish the amount of performance degradation
model, HYD-QUAD. CECW-B should be
that has occurred. Original levels of performance
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