ABSTRACT
Symmetrical components are the traditional method used to calculate short-circuit currents and voltages for AC power systems. Dr. C. L. Fortescue developed this method while investigating problems of singlephase railway systems in 1918. Symmetrical components allow the use of single-phase “loop” or “node” equations to develop short-circuit currents and voltages on single-phase, two-phase, or three-phase systems. The big advantage of symmetrical components is the elimination of the need to include transformer turns ratios and winding connections in calculations. (Transformer data is used to develop base values and to incorporate phase shifts into calculations.)
Three-phase loop or node equations can be used to calculate short-circuit values on simple power systems (one machine, one line, one transformer). However, for the typical power system, loop and node equations become unwieldy, even with today’s computing capability, because transformer turns ratios and transformer winding connections need to be included when traditional loop (Kirchoff’s Laws) and node (Norton’s Laws) calculations are used for circuit analysis.
