Society is becoming increasingly dependent on a cost-effective reliabl
e electric power supply, Unreliable electric power supplies can be ext
remely costly to electric utilities and their customers, Predictive re
liability assessment combines historical outage data and mathematical
models to estimate the performance of specific network and system conf
igurations [e.g., IEEE Std, 493-1990], This paper is concerned with th
e value-based assessment of proposed modifications to an existing indu
strial distribution system configuration to minimize the costs of inte
rruptions to both the utility and its industrial customers, This paper
will present a series of case studies of an actual industrial load ar
ea supplied by two feeder circuits originating from two alternate subs
tations, Each case study will reveal the impact on the cost of industr
ial load point interruptions and the frequency and duration of industr
ial load point interruptions when various system constraints (e.g., id
eal and nonideal protection coordination schemes, substation capacity
restrictions, etc.) are imposed on the distribution system, The paper
discusses in some detail the variance in reliability performance index
es and their impact on the cost of load point interruptions, A basic c
onclusion of this paper is that expansion plans of an industrial distr
ibution system can be optimized in terms of reliability by using an ec
onomic criterion in which the sum of both the industrial facility inte
rruptions and the utility system costs are minimized.