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The effects of interphase coupling in multiphase power systems become important in the presence of network topology imbalance and unbalanced phase loadings. Currents that flow in the earth can have significant effects on the system's behavior. Both of these effects of imbalance must be accounted for in an accurate model of a multiphase system. A step-by-step procedure for unbalanced power system modeling is presented. The procedure relies upon linear graph theory and produces a multiport model which is a generalization of the well-known bus admittance model. This paper reviews some important results of linear graph theory and gives sufficient detail that the procedure can be followed without extensive use of the references (whose nomenclatures differ). Mutual coupling effects, the effects of neutral and static conductors, the finite conductivity of earth, and various component models are considered. A companion paper describes a procedure for reducing the order of the power system model.
Date of Publication: Oct. 1985