Transformer Nameplate Rating:
Transformer Nameplate Rating – The voltage ratio is specified as V1 (rated)/V2 (rated). It means that when voltage V1 (rated) is applied to the primary, the secondary voltage on fullload at specified pf is V2 (rated).
The ratio V1 (rated)/V2 (rated) is not exactly equal to N1/N2, because of voltage drops in the primary and secondary. These drops being small are neglected and it is assumed that for all practical purposes
The rating of the transformer is specified in units of VA/kVA/MVA depending upon its size.
where V and I are referred to one particular side. The effect of the excitation current is of course ignored.
The Transformer Nameplate Rating also specifies the equivalent impedance, but not in actual ohm. It is expressed as the percentage voltage drop expressed as
where all quantities must be referred to any one side.