IEEE Power & Energy Magazine - January/February 2016 - 20

users" associated with different levels of
generating system reliability and the determination of optimal capacity reserve
margins. Key factors in value based reliability assessment (VBRA) are the costs
associated with system failure and the
residual uncertainties associated with
assessing this cost.
The paper "Comprehensive Bibliography on Electric Service Interruption
Costs" (R. Billinton, G. Wacker, and E.

Wojczyski, IEEE Transactions on Power
Apparatus and Systems, vol. PAS-102,
no. 6, June 1983) contains a wide array
of publications relating to the theory and
results of research into reliability worth.
Another paper, "Comprehensive Bibliography on Reliability Worth and Electric
Service Consumer Interruption Costs:
1980-1990" (G. Tollefson, R. Billinton,
and G. Wacker, IEEE Transactions on
Power Systems, vol. 6, no. 4, November

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1991, pp. 1508-1514), extended the list
of available material on this subject.
International interest in this area is documented in a CIGRE Report, "Methods
to Consider Customer Interruption Cost
in Power System Analysis," compiled
by CIGRE Task Force 38.06.01 with
representation from 14 countries.
Data obtained from a series of customer sector surveys were subsequently used in a VBRA study of Ontario
Hydro's generating capacity adequacy
criterion and the optimum capacity reserve margin. This activity was called
the System Expansion Program Reassessment (SEPR) study and examined
generation system reliability and other
issues. The SEPR study included analyses of generation expansion programs
with capacity reserves varying from 18
to 38%. The total system cost profile,
which includes expected customer
outage costs, shows relatively little
change in the minimum total cost over
a range of reliability levels. The judgement was made that it is preferable to
be on the higher reliability end of the
minimum portion of the curve rather
than on the lower end. The decision
was driven by the idea of recognizing
unquantified risk not covered by the
analytical model and the fact that total
customer costs increase more rapidly
at lower reliability levels than at higher
levels. The costs associated with having a little too much reserve is considerably smaller than not having enough
reserve. It was also recognized that estimating customer interruption costs is
an imprecise process involving a large
amount of experience and judgment.
The basic conclusions regarding the
nature of the total system costs profile
as a function of the reserve capacity
margin are supported by a study conducted by the Electric Power Research
Institute (EPRI), "Costs and Benefits
of Over/Under Capacity in Electric
Power System Planning" (EPRI EA927, Project 1107 Final Report, October 1978). The report shows results
for four participating utilities (LILCO,
TVA, PG&E, WEPCO). In each case,
(continued on p. 124)
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