Coherency Based System Decomposition into Study and External Areas Using Weak Coupling

The transient stability studies of large power systems are normally obtained, by dividing the system into study and external areas. In this paper, a systematic procedure is proposed via the joint application of the concepts of weak coupling and small perturbation. The suggested procedure determines weakly coupled areas in the system which are seen to contain weakly coherent machines. The procedure also identifies strongly coherent machine groups within weakly coherent areas. The technique has been applied for a system decomposition for the power grid of northern India containing 50 machines. The accuracy of the method is tested by comparing the swing curves obtained via a simulation study. This comparison validates the coherent behaviour of the machines in the predicted groups.