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Conventional under-frequency load-shedding scheme is designed to retrieve the balance of generation and consumption following a disturbance. In the conventional load-shedding method, frequency settings, time-delay settings and the amount of load to be shed in each step are constant values. The loads to be shed by this scheme are also constant load feeders and not selected adaptively. This constant non-adaptive load-shedding algorithm is not the most efficient scheme for all power system disturbances. Application of centralised load-shedding algorithms could enhance adaptability of the load-shedding schemes. Two centralised adaptive load-shedding algorithms are proposed. The first algorithm is response-based and the second one is a combination of event-based and response-based methods. The proposed methods are capable of preserving power system instability even for large disturbances and combinational events. They use both frequency and voltage variables to select appropriate amount of load shedding. Parameters of the suggested schemes are also selected adaptively based on the magnitude of the disturbance. Performances of the proposed algorithms are evaluated by the application of the adaptive algorithms to the distributed and dynamic simulated model of a real power system. Obtained simulation results confirm that by using these algorithms various power system blackouts may be prevented.