Towards Optimized Distribution Protection Design

Traditionally, distribution systems engineering has focused on simplified design criteria guided by individual utility practices and experience. These designs were not optimized but did satisfy specific regulatory goals for system performance. Two developments are invalidating this approach: deregulation of the industry and rapid improvements in technology. Deregulation forces utilities to more carefully consider the cost of providing reliable service and to be concerned with the customer cost of reliability. At the same time, microprocessor based devices have greatly expanded the capabilities of protection apparatus. Further, low cost high speed computers have rendered computer aided design tools feasible. In this paper, distribution feeder protection is formulated as a reliability problem. Distribution reliability indices appropriate for protection design are discussed. Indices which are impacted by protection design are identified. The authors propose a new approach to optimizing overall distribution system protection design.