An impact increments-based state enumeration reliability assessment approach and its application in transmission systems

This paper proposes an impact increments-based state enumeration (IISE) reliability assessment approach, specially designed for transmission systems. Firstly, the reliability index calculation formula of the traditional state enumeration technique is transformed into an impact increments-based formation. With the derived formula, the calculation of state probability is simplified and the weight of low order contingency states is increased. Moreover, it is proved in this paper that impact increments of mutually independent high order contingency states, whose outage components are with remote distances, can be eliminated. Due to this fact, the calculation of impacts of most high order contingencies can be reduced without decreasing the precision of reliability indices. When applied to electrical power transmission systems, load variations can also be considered by replacing impact increments by their expectations under various load levels. Thus, annual reliability indices can be obtained by the proposed method. Case studies are performed on the IEEE-118 bus system and a 1354-bus portion of European transmission system from PEGASE project. Results indicate that annual reliability indices can be efficiently obtained with IISE method. Comparing with the traditional state enumeration and Monte Carlo simulation methods, the proposed method is more precise and efficient in various kinds of transmission systems.