Calculating Short Circuit Current

Use the voltage that is applicable to where you are calculating the short circuit occurring (this information should be expressed in the example you are trying to answer).

If the transformer is a step down transformer (eg- the transformer is fed from the 480V side) and the short circuit is on the secondary (277V side) then you use 277V.

Given your simplified example the short circuit is likely on the secondary 277V side.

I think the KVA is the rating of the Transformer in your above formula,if so the formula will give you the full load current of the transformer.if you take el-l=277 then the full load current will be of LV side.

if you take EL-L=480 then the full load current will be of HV side.

In the above example the kva is assumed to Rating of the transformer.

The Short circuit KVA/MVA of the transformer to be calculated based on %Z of the transformer.

Short circuit current can be calculated using the same formula but the KVA to be replaced with Shortcircuit KVA.