chapter  1
42 Pages

Short-Circuit Currents and Symmetrical Components

WithJ.C. Das

Short-circuit calculations are the primary study whenever a new power system is designed or an expansion and upgrade of an existing system are planned. A simple explanation of the origin of the transient component is that in power systems the inductive component of the impedance is high. The impedances presented by various power system components, that is, transformers, generators, and transmission lines, to symmetrical components are decoupled from each other, resulting in independent networks for each component. The transient analysis of the short circuit of a passive impedance connected to an alternating current source gives an initial insight into the nature of the short-circuit currents. The method of symmetrical components has been widely used in the analysis of unbalanced three-phase systems, unsymmetrical short-circuit currents, and rotating electro-dynamic machinery. 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.