Overall approach to the reliability evaluation of composite generation and transmission systems

The reliability evaluation of combined generation and transmission systems is presently receiving considerable attention as utilities are finding it increasingly necessary to quantitatively evaluate individual busbar and overall system reliability indices. This paper presents an overview of the problem and describes a technique developed at the University of Saskatchewan which evaluates the busbar and system reliability indices by considering all possible simultaneous (or overlapping) independent outage combinations of generating units, transmission lines and transformers. The indices are calculated after alleviating line overloads, generator MVAr overloads etc. arising because of outage situations. Common-mode or common-cause outages of two transmission lines on the same right-of-way, or on the transmission tower, are also included in the analysis. A digital computer program developed for evaluating the reliability of a composite generation and transmission system is also described. The program can, at present, consider common-cause outages and all possible first and second order simultaneous independent outages. The effectiveness of the technique is illustrated by application to a 30-busbar model of a practical power system.