Fast computation of post-contingency system margins for voltage stability assessments of large-scale power systems

A technique to compute the post-contingency system margins for power system voltage stability assessment is presented. The voltage collapse point of the system base case is first computed using a traditional PV curve method. When a contingency is applied to this fully stressed base case, loads must be shed in order to maintain voltage stability. The key idea of the proposed method is to determine the right amount of load shedding that leaves the post-contingency system at its nose point. The system margin is equal to the base case margin minus the load shedding amount. The amount of load to shed is computed by a modified power flow method, where the amount of load shedding is parameterised by an additional unknown variable. The technique has been tested on a large-scale power system with 1725 buses. The results show that the proposed approach is very efficient for voltage stability assessment when a large number of contingencies are involved