Achieving distribution feeder reliability using benefit/cost ratio analysis

The authors describe a computer-based method for evaluating the benefit/cost ratios associated with projects for improving distribution feeder reliability. A reliability benefit is expressed in terms of a change in the feeder average interruption frequency index (FAIFI) of the feeder average interruption duration index (FAIDI). Cost is expressed in terms of the levelized annual revenue requirement associated with the reliability improvement project. The essential tool for the method of the paper is the distribution reliability assessment model (DREAM), a spread-sheet-type computer program, used to compute values for FAIFI and FAIDI. This model utilizes as inputs the feeder configuration, customers and components connected, component failure rates, and response and repair times. A Pacific Gas and Electric Company underground feeder (Edenvale 1106) is used to illustrate the impact of benefit/cost analysis on a feeder reliability improvement program. It is shown that fully 50% of the values of the indices (FAIFI and FAIDI) are contributed by only 10% of the line sections. Further, the indices are most sensitive to failure rates of HMW polyethylene cable, transformers, and switches. It is found that automatic sectionalization of the line sections which contribute most heavily to the indices is the most cost-effective strategy for reliability improvement