Reliability Calculations for Electrical Transmission Systems on the Basis of Mean Failure Indices

In an electric power transmission network, a fault occurring on any one of its components sometimes causes an´ active event´ as a result of interaction between the power system and its protection system. An outage of sections adjacent to the faulted one for a small duration is characteristic of these events. In this paper, the mean failure indices (mean probability-of-failure and mean frequency-of-failure) of a network are defined as functions of the failure indices at various load points. Several types of active events including those caused by failure of protection system are considered and their contribution to the mean failure indices of the network evaluated. The effectiveness of providing normally open paths in reducing the mean failure indices of the network is explained. The points are illustrated by examples.