(i) Heat losses in the windings of transformer. They are minimised by taking a thicker wire in primary coil than in the secondary coil in a step up transformer, whereas a thicker wire in secondary coil than in primary coil in a step-down transformer.
(ii) Hysteresis losses in the core of transformer. They are minimised by using soft iron core.
(iii) Eddy current losses in the core of transformer. They are minimised by taking the core laminated instead of taking it as one solid piece.