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For the operators of a power system, underfrequency load shedding is important for maintaining the system in a stable and reliable state whenever it suffers from a severe disturbance. The underfrequency relay protects the power system against a blackout when the system frequency declines to predetermined settings. This paper determines the shed load at each stage for the underfrequency relay (81L). The genetic algorithm (GA) is employed to minimize the shed load and maximize the lowest swing frequency. Penalty functions and chromosomes with varying lengths are utilized in the GA to determine the optimal shed loads at all stages. The uncertainty in bus loads is modeled by a fuzzy set. A stand-alone power system with diesel and wind-power generators is adopted to demonstrate the applicability of the proposed method.
Date of Publication: Jan. 2012