Development and application of probabilistic criteria in value-based transmission system adequacy assessment

In the past, electric utilities were continuously adding more facilities to their systems in order to satisfy the growing customer energy requirements based on a set of deterministic criteria that guide transmission planning. The traditional planning guidelines were based on planner´s experience and intuition without a formal and consistent framework for their development. In most cases, using the deterministic criteria, the systems were either over or under built. In the deregulated market, any investment decision related to transmission reliability required to be addressed on a rational and quantitative basis within a cost-benefit framework explicitly using data on the value of changes in service reliability to customers. The ultimate determination of poor or adequate transmission reliability performance in the cost-benefit planning framework is based on customer´s preferences and customer mix that are unique to each transmission system. In the current competitive energy market environment, such an approach makes perfect sense. This paper presents an approach to rank the deterministic contingencies using a relative likelihood approach to the most frequent contingency of a generator outage and assign required system steady state performance requirements against high, medium and low probability contingencies. The paper then illustrates the applications of the probability based criteria in value-based transmission system reliability enhancement planning using a practical transmission system.