CALCULATION OF FAULT LEVEL

You will need many parameters - incoming fault leven, transformer impedance, impedances of all components within the substaion, busbars, switchgear, cables etc..

try this one for starters -

http://www.waset.org/journals/waset/v48/v48-73.pdf

What is the maximum & minimum fault lavel of a 400KV S/s? How it is calculated? If we know the Phase to phase & phase to ground fault MVA of a S/s how can we calculate maximum & minimum fault of the S/s?