### KVA of Single phase Transformers

As stated above, line maximum current (kA) and maximum phase voltage(kV) for single phase transformer is directly measurable. Transformer output maximum current and output maximum voltage are obtained for this calculation.

Apparent \, power (S) = Current (I) * Voltage (V) = VI

### KVA of Three phase Transformers

For three phase transformers, KVA or MVA is calculated as follows.

There are three phases, so three individual apparent powers are added to get the transformer apparent power.

That is,

Apparent \, power (S) = 3\times \frac{V}{\sqrt{3}}\times I = \sqrt{3}VI