Experiment with transformer: meaning of some physical quantities
This shows the Mutual Inductance which typically draws a VAR power 10% of rated VA so the input current is low P.F.

The short circuit current Isc is then the Rated VA/Zpu so a Zpu=10% of Rated V/I max at full load is 10% of Isc or  

Isc =  ( V  * A )/Zpu