Transformer Short circuit calculation at Secondary terminals

• In a simplified approach, the impedance of the MV system is assumed to be negligibly small, so that:

${\displaystyle Isc={\frac {In\times 100}{Usc}}}$

where

${\displaystyle In={\frac {S\times 10^{3}}{U_{20}{\sqrt {3}}}}}$

and:

S = kVA rating of the transformer
U20 = phase-to-phase secondary no-load voltage
In = rated current of the transformer
Isc = short-circuit current in amps
Usc = short-circuit impedance voltage of the transformer in %.