- The copper loss (I2R) in the transformer depends on the current through the winding.
- The iron loss or core loss of the transformer core depends on the voltage as frequency of operation is constant.
- None of these losses depends on the power factor(cos Φ) of the load.
- So losses decide the temperature rise and hence the rating of the transformer.
- As the losses depends on V and I only, the rating of the transformer is specified as the product
- of these two parameters (V x I).
- Thus the transformer rating is in KVA and not in KW.