This paper presents a topology-based scheme for adaptive underfrequency load shedding (UFLS). By tracking changes of power system topology and information about power flow, the proposed method is able to identify islanded conditions, the number of islands and their deficits of active power, which are fundamental parameters for the adaptive UFLS scheme. The algorithm is also applicable to interconnected power systems, where islanding of the power grid can go beyond country borders and create new asynchronous areas that can comprise several national transmission systems. In this case, the proposed method can properly estimate the power deficit of each area and coordinate the load shedding of several affected power systems in the underfrequency area. The main idea of the proposed method is demonstrated by simulations of the IEEE reliability test system in PSS/E and real time coordination of the adaptive UFLS schemes in Labview.
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