What are the losses in a single-phase transformer?

A transformer has no moving parts, so there are no mechanical losses. The losses are:

1. Iron (core) losses P_i — occur in the core due to alternating flux; practically constant at all loads (measured by open-circuit test).
   • Hysteresis loss \( P_h = k_hB_m^{1.6}fV \) — due to repeated magnetisation reversal; reduced by using silicon steel.
   • Eddy current loss \( P_e = k_eB_m^2f^2t^2V \) — due to circulating currents induced in the core; reduced by using thin insulated laminations.
2. Copper losses P_cu — I²R loss in primary and secondary windings: \( P_{cu} = I_1^2R_1 + I_2^2R_2 = I_1^2R_{01} \); varies with the square of the load current (measured by short-circuit test).
3. Minor: stray (leakage flux) losses and dielectric loss in insulation.

Total loss = P_i + x²P_cu,FL; maximum efficiency when copper loss = iron loss.