Answer / vipul parmar

STC Means Short time current. it s calculated from transformer Impedance.
there are difference stc rating like 18.3ka ,26.3ka ,31.4ka ,40ka.
Electrical Power Systems in industrial plants are designated to serve loads in a
safe and reliable manner. One of the major considerations in the design of a
power system is adequate control of short circuits.
Three-phase short circuits usually produce the highest magnitude of current the
power system equipment must be able to withstand. Phase to ground short
circuit currents might occasionally be higher than three-phase short circuits
currents in systems with multiple-point solid neutral grounding. In general,
power systems in industrial facilities, which employ single-point solid grounding
or resistance grounding, require only a three phase fault current calculation to
determine current magnitudes for proper fault interrupter application and for
protective device coordination studies. However, this study considers also the,
phase to phase, phase to ground and phase to phase to ground short circuit as a
reference.

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