Which types of losses in a transformer are equal to each other, resulting in maximum efficiency of the transformer? 

There are mainly two kinds of loss that occurs in transformer, which is given,

Copper loss:

A loss in a transformer that takes place in the winding resistance of a transformer is known as the copper loss.

Copper loss = i2R

These are variable losses.

Iron loss:

Iron losses = Eddy current loss + hysteresis loss

Eddy current loss = Ket2f2B2

Hysteresis loss = KhfBx

These are constant losses.

Efficiency: The efficiency is the ratio of output power to the input power.

The efficiency (η) of the Transformer is given as,

 \(η = \frac{{XS\cos \phi }}{{XS\cos \phi + {P_i} + {X^2}{P_e}}}\)   .... (1)

Where, X = Fraction of load

S = Apparent power in kVA

Pi = Iron losses

Pcu = Copper losses

The transformer will give the maximum efficiency when their copper loss is equal to the iron loss.