Conceptual framework for assessing reliability of subtransmission systems based on severity indices

This paper proposes a comprehensive framework for defining operational classification criteria to evaluate the performance of electric power subtransmission systems. Based on the reliability indices estimated fora system taken as a reference and least squares regression analysis, an efficient way of classifying the adequacy of subtransmission networks is established. Using the proposed method, a judgmental scale for measuring the degree of severity index is obtained, which allows a quick check of the network's operational performance, something that does not currently exist for subtransmission networks. The severity index is expressed in system minutes, i.e., the ratio between the expected unsupplied energy and the annual system peak load. The definition of an appropriate classification criterion represents an important support for decision making processes in the context of network planning and operation. Four real subtransmission systems, operated under a concession regulation by the same Brazilian public utility, are used to illustrate and analyze the use of the proposed method, and the obtained results are discussed.