Three different impedance networks are formed to calculate momentary, interrupting, and steady-state short circuit currents, and corresponding fault current duties for various protective devices. These networks are: ½ cycle network (subtransient network), 1.5-4 cycle network (transient network), and 30 cycle network (steady-state network).
ANSI/IEEE Standards recommend the use of separate R and X networks to calculate X/R values. An X/R ratio is obtained for each individual faulted bus and short circuit current. This X/R ratio is then used to determine the multiplying factor to account for the system DC offset.
Short Circuit Analysis Software ANSI & IEEE Toolbar