System protection scheme for mitigation of cascaded voltage collapses

A system protection scheme is proposed to mitigate cascaded voltage collapses. Based on the post-contingency conditions of either existence or non-existence of an equilibrium solution, and with regard to the stability and security criteria, the proposed scheme finds the optimal set of remedies. The proposed stabilising scheme brings the non-equilibrium post-contingency operating point back inside a stable region, and then passes this point to the securing scheme. Also, to enhance the performance of the stabilising scheme, a sensitivity analysis method is presented to detect the most effective remedies. The proposed securing scheme converts the stable, but insecure operating point, to a secure and stable one. Inclusion of the contingencies in the voltage security problem increases its difficult and, hence, the Benders decomposition method is used for this purpose. Also, a voltage stability indicator is proposed to monitor the available margin to the collapse point. Both the mathematical models of the stabilising and securing schemes are solved using the sequential quadratic programming technique over the IEEE 30-bus and IEEE 118-bus test cases.