Fundamental Concepts of Symmetrical Components

A system of three coplanar vectors is defined by six parameters, and the system possesses six degrees of freedom. The impedance encountered by the symmetrical components depends on the type of power system equipment, that is, a generator, a transformer, or a transmission line. While estimating sequence impedances of power system components is one problem, constructing the zero, positive, and negative sequence impedance networks is the first step for unsymmetrical fault current calculations. Zero sequence currents flow only in zero sequence networks and not in positive or negative sequence networks. Therefore, it becomes necessary to construct positive, negative, and zero sequence networks. For a study involving sequence components, the sequence impedance data can be calculated by using subroutine computer programs, calculated by long???hand calculations, or estimated from tables in published references. Discussions in the chapter also include Wye???Wye transformers, Delta???Delta transformers, Wye???Delta transformers, and Zigzag transformers.