ETL 1110-2-550
30 May 97
Appendix B
should be performed. For equipment with extensive
Reliability Study Process
life databases, such as generators and turbines,
standard time-dependent reliability and hazard
functions should be used. These functions are under
development by Institute for Water Resources
B-1. A reliability analysis of hydropower plant
(IWR) and HDC. Any of the weaknesses and
equipment requires the following three basic steps:
concerns identified in the previous steps should be
(a) data collection and investigations; (b) identi-
fully explained and addressed separately if required.
fication of specific reliability issues; and (c) cal-
culations and evaluation. Figures B-1 and B-2
show the basic steps in a reliability study and the
B-2. There may clearly be a failure history of
typical hydropower equipment analyzed for
specific equipment which warrants a reliability
reliability.
analysis separate from the remainder of the
equipment. The generators at The Dalles
a. The data collection and investigations need
powerhouse demonstrated a specific failure mode
to be extensive and cover all aspects of the
(coil failure from turn-to-turn faults) and a severe
equipment design, use, history, and future demands.
decline in reliability after fifteen years of age.
This step should include historical unit availability
Weibull curves were developed for the generators
and operation, any equipment derating, accident
since the historical data of the fourteen units, for
reports, operation and maintenance records,
which there had been thirteen coil failures,
equipment performance tests (original, interim, and
constituted a sufficient database (USACE 1995).
current), periodic inspection reports, design and
Specific equipment curves can be developed by
construction reports, the operation and maintenance
adjusting the standard equipment curves if the
manual, and turbine model test reports. During this
equipment demonstrates accelerated degradation,
step it is also important to identify the priorities and
such as was found at the Buford powerhouse. A
concerns of the project personnel and utilize
reliability study of the Buford turbines found that
engineering judgment in evaluating equipment
the condition of the main unit turbines was typical
condition. A thorough site investigation should be
for their age, but the station service unit showed
conducted by hydropower technical experts and
severe degradation (USACE 1996). Therefore, it
should include equipment inspections and project
was reasonable to use the standard reliability and
personnel interviews.
hazard functions for the main units and adjust these
functions to reflect the poor state of the station
b. The data should then be compiled and the
service unit. If the equipment has a specific
primary equipment weaknesses and project
reliability problem but lacks a statistically
concerns identified. The equipment condition may
significant base of data, a capacity versus demand
be quantified with the Condition Indicator (CI)
analysis may be done. This approach was appro-
value as defined in the REMR Condition Rating
priate for the reliability analysis of the Walter F.
Procedures (USACE 1993). In addition to the CI
George powerhouse. The turbines were found to
value, the equipment operation, demands, and
have two areas which warranted further assessment,
maintenance practices should be considered in
the shaft sleeve and hub, so JAYCOR was con-
evaluating the reliability. Experience and historical
tracted to provide a full report (Mlaker and Bryant
data of like equipment should be utilized in the
1994).
determination of the equipment condition and future
reliability.
B-3. To obtain the most current time-dependent
c. Once the condition of the equipment has
reliability research results, contact the HDC.
been identified, the calculations and evaluation
B-1
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