Occur same as in distribution line and are lesser in quantity as compared to core losses.
Copper losses are nothing but dissipated heat by the current in primary as well as secondary winding which can be found out by the current square relation with resistance.
Any factor affecting current and winding resistance obviously affects copper loss in the transformer.
Increase in real or reactive loading causes more flow of current hence more copper losses.
Resistances of winding depends upon length and size of winding conductors.
This has an important contribution in the amount of copper loss in the transformer.
Change in temperature of the winding causes changes in resistivity of the winding conductors hence overall resistance hence copper losses of the transformer.
