[danar]

MVA fault Rating.. How this Fault rating is Calculated?

[sathe1963]

dear danar,
your answer is pending from April 08. Fault mva = base mva / % impedance.
With this formula one can calculate fault mva. Once we get mva then a to be calculated with reference to voltage. Thus one will get fault current. If one or more than one are feedeing / generating in parallel, then impedances of all machins to be calculated by parallel way.

[I Newton]

The load side of the transformer is shorted out.

A variable voltage is applied to the transformer to the point when the transformer reaches full load current.

If the transformer is 11kV
If the full load current is 1000A

If the applied voltqage on the shorted out transformer is 5% of 11kV to achieve the 1000A than the impedance is 5%

If 5% voltage produces 1000A on a short circuti fault, than 100% voltage i.e. 11kV will produce 20 times the full load current i.e. 20,000A