In the study of large interconnected power systems, it is essential to aggregate, the power system into several parts, such that each part represents a number of generators. In the words, the coherent generators lie in one part. In this paper, the coherent generators are determined using a pattern recognition technique called hierarchical clustering method. In this method, firstly, rotor angles of the generators are obtained based on transient stability technique which are calculated by solving state space model of system during three phase short circuit fault Then, the coherency measure which is the similarity matrix is formed using the rotor angles. After that the coherent generators are determined using hierarchical clustering method. The proposed method is then applied to the 39-Bus New England test system. Results of the simulation show that this method is capable in finding the coherent generators in the power system.

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