Due to which reasons the energy losses do occurs in actual transformer ?

Explanation

(i) Flux Leakage `:` Not all of the flux due to primary passes through the secondary due to poor design of the core or the air gaps in the core. It can be reduced by winding the primary and secondary coils one over the other.
(ii) Resistance of the windings `:` The wire used for the winding has some resistance and so, energy is lost due to heat produced in the wire `I^(2) R`. In high current, low voltage windings theses are minimised by using thick wire.
(iii) Eddy Currents `:` The alternating magnetic flux induces eddy currents in the iron core and causes heating. The effect is reduced by having a laminated coil.
(iv) Hysterests `:` The magnetisation of the core is repeated reversed by the alternating magnetic field. The resulting expenditure of energy in the core appears as heat and is kept to a minimum by using a magnetic material which has a low hysteresis loss.
(v) Transformer work on AC voltage hence in each cycle, the length of ocre increases and decreases. As a result transformer produces buzz noise. So, some electric energy dissipated in buzz noise.