chapter  7
50 Pages

Short-Circuit Calculations according to ANSI Standards

WithJ.C. Das

American National Standards Institute (ANSI) methods of short-circuit calculations are used all over North America and are accepted in many other countries. These standards have been around for a much longer time than any other standard in the world. The worst short-circuit conditions occur at maximum loads, because the rotating loads contribute to the short-circuit currents. The worst short-circuit conditions occur at maximum loads, because the rotating loads contribute to the short-circuit currents. The short-circuit calculations are normally carried out at the rated voltage. Irrespective of the type of fault current calculation, the power system is reduced to single Thevenin equivalent impedance behind the source voltage. The source voltage or prefault voltage is the system rated voltage, though a higher or lower voltage can be used in the calculations. Depending on the type of calculation, the ANSI/IEEE standards consider that the dynamic reactances are multiplied by factors.