A method for bulk power system reliability evaluation based on local coherency

The problem of bulk power system reliability evaluation is considered and a new solution approach is proposed. Bulk power system models are generally not coherent in the sense of reliability theory. Conditions are derived on network topology to guarantee coherency. Only parallel structure systems satisfy these conditions. Noncoherency of a power system may be the effect of only a subset of its transmission lines. Thus the concept of local coherency is introduced. A decomposition approach to bulk power system reliability evaluation based on the concept of local coherency is developed. Sufficient conditions for local coherency are derived.