Determination of reliability worth for distribution system planning

There is an ever growing demand to justify reliability projects on a more quantifiable basis, i.e. investments related to the provision of service reliability needs to be carefully evaluated in regard to their cost and benefit implications. In addition, utilities are recognizing the significant customer and community costs that are incurred when electric supply is abruptly curtailed. Consequently, the utility industry is under pressure to assess their reliability evaluation tools and formulate methods for incorporating the economics of reliability in the decision-making process. This paper is concerned with the evaluation of a reliability worth index that can be used to make decisions in distribution system planning and design. The reliability worth index is termed the interrupted energy assessment rate (IEAR) and is obtained by relating the reliability indices to the customer cost of interruption data. Three fundamentally different approaches for evaluating distribution system reliability worth indices are presented and compared using a small but comprehensive test system. The impact on the worth indices of distribution system operating policies and configurations is also illustrated using the three methods. The worth indices developed can be used to determine the monetary implications of customer supply interruptions thereby incorporating economics in the reliability cost-benefit equation