New Local Adaptive Load-shedding Methods to Mitigate Power System Blackouts

Under-frequency load shedding is a globally accepted remedial measure against a severe drop of power system frequency. With the ever-increasing size of power systems, severe frequency drops are usually caused by combinational severe disturbances. For such disturbances, the active power deficit is usually accompanied by a reactive power deficit presenting some challenges to the load-shedding protection schemes. In this article, two adaptive combinational load-shedding methods are proposed that enhance the frequency and voltage security of power systems for such disturbances. In the proposed algorithms, the under-frequency load-shedding scheme is modified so that the load shedding is adaptively started from locations that have a lower voltage stability margin. Besides, the speed of load shedding is changed adaptively depending on the voltage stability status of the system and the rate of frequency decline. The proposed methods use locally measured frequency and voltage signals and are, therefore, easily applicable. Performance of the proposed load-shedding methods has been compared to that of the conventional method for various disturbances in two different systems. Obtained simulation results confirm that by using the proposed algorithms the power system becomes more robust against large disturbances and the probability of the power system instability is decreased.