A method of voltage stability evaluation for branch and generator outage contingencies

This paper proposes a fast computation method to evaluate the load power margins with respect to saddle node bifurcations under branch outage as well as generator outage contingencies. The voltage stability evaluation for generator outages is a new topic, while there exist various studies for the branch outage contingencies. The proposed method is based on the conventional linear sensitivity method. The linear estimations are improved by taking into account nonlinearities of the power flow equations and by using a fast line search technique. Compared with existing methods, the accuracy is considerably improved. The effectiveness of the proposed method is demonstrated through IEEE 14-, 30-, and 57-bus systems. The estimation errors in load power margins are not more than 5% for generator outage and 15% for all branch outage (route open outage) contingencies.