Power system reliability assessment: Implementation of common-cause failures

This paper presents an improved probabilistic method for power system reliability assessment. The new method enables consideration that several generating units may share the same source of failure, e.g. design fault of the same manufacturer, or a coupling mechanism, e.g. lightning strike, that creates certain condition causing them to fail or become unavailable simultaneously. The improvements are achieved by the implementation of common-cause failures, where the Multiple Greek Letter model is used. This paper includes a mathematical derivation of the presented method. The theory is then applied to a simplified realistic power system. The results show that the new method enables more detailed power system reliability analyses. The results also show that the estimated power system reliability decreases, if common-cause failures of several generating units are considered.