New Centralized Adaptive Under Frequency Load Shedding Algorithms

In this paper two centralized adaptive under frequency load shedding algorithms are proposed and analyzed. The objective of these methods is to simultaneously protect power systems against frequency instability as well as voltage instability, following combinational disturbances. After some events in power systems frequency starts to recover, while the system collapses due to voltage instability. This situation may occur due to high dependence of loads upon voltage, low frequency settings of under frequency relays, slow operation of under frequency relays and inappropriate selection of either amount or location of loads to be shed by conventional UFLS relays. The load shedding algorithms of this paper attempt to overcome the above mentioned shortcomings of conventional UFLS method. Performances of the proposed algorithms are evaluated by application of adaptive algorithms to the distributed and dynamic simulated model of a real power system test case.