Underground Distribution System Design for Reliability

The extent to which underground distribution systems are now being constructed and planned for the future necessitates identifying a preferred design consistent with present performance requirements and minimum cost objectives. This study analyzes many variations in design of a representative underground distribution circuit from these viewpoints. This analysis consists of a step-by-step procedure using specific work functions to synthesize interruption times resulting from both planned and forced outages. The designs considered represent variations in application of fault indicators, fault interrupters, and load-break switches. Development of circuit outage rates permits identification of annual interruption rates as seen by the average customer and by the last customer restored to service. Relating this performance of each circuit design investigated to the incremental cost associated with that design permits identification of an overall preferred design.