Power system dynamic vulnerability under extreme transmission line contingencies

Power systems around the world may be under the threat of extreme conditions such as natural disasters and terrorist attacks. To find the most severe condition in the static sense, systematic methods based on optimization have been developed. However, until now, there is no systematic way to find the most severe contingency in the dynamic sense. The thesis proposes such a systematic approach. The method adopts a two-step "screening-and-ranking" procedure similar to the one employed in conventional dynamic security analysis.;Test results on the One Area IEEE96 system show that the set of critical lines selected by the proposed screening scheme is dependent on the system operating conditions. The screening step can reduce the contingency number significantly, which will alleviate the computation burden in the ranking step by a large margin. The most severe contingencies in term of load shedding were in most cases identified by the proposed method. The merit of the method is its simplicity, which makes it applicable to the analysis of N-2 and N-3 transmission line contingencies. Limitations of the method, such as the possibility of missing the more disruptive cases and the influence of the power system structure on its effectiveness, are also discussed.;In the "screening" step, transmission lines are screened using two criteria. The first criterion is based on critical eigen-sensitivity with respect to single line outages. A transmission line is selected only if one of the critical eigenvalues has a large sensitivity to the outage of this line. The second criterion is based on a topology analysis searching for cut-sets in the system. A transmission line is selected if it is a member of a system cut-set with high power imbalance ratio. In the "ranking" step, time-domain analysis is performed on all the combinations of the lines screened by the first step, to determine their real dynamic impact on the system. Relays for generators, loads, and transmission lines are set-up so as to capture possible cascading events after the initial disturbance.