Centralized load shedding based on thermal limit of transmission lines against cascading events

Load shedding is the last and most expensive control action against system collapse and blackout. Achievement of an efficient emergency control to stabilize the power system following severe disturbances, requires two key objectives. First, prevention of cascading outages, i.e. saving the available and determinant power system elements, and second, issuing proper control actions to stabilize the power system inside the permissible time frame. In this paper, the loading rate of transmission lines are continuously monitored and the maximum available time prior to the outage of lines due to operation of their over current protection relay are calculated. The load shedding as the only available control action is applied to the loads connected to the ending of most overloaded transmission lines and with minimum time until outage. This approach reliefs the thermal limit of lines leading to secure and reliable operation of transmission lines. Load shedding locations are continuously updated online based on loading rate/thermal limit of lines to prevent their outage. Simulation of severe contingencies carried out on 39 bus IEEE standard test system in DIgSILENT PowerFactory software validates the efficiency of proposed method.