In transformers some power is always lost due to, heating effect, magnetic flux leakage, eddy currents, hystersis and humming.
(i) Cu loos (i2R) : When current flows through the transformer windings some power is lost in the form of heat (H = I2 Rt). To minizie this loss windings are made of thick wires (to reduce resistance)
(ii) Eddy Current loss : Some electrical power is wasted in the form of heat due to eddy currents induced in core, to minimize this loss transformers core are laminated and silicon is used as the core material as it increases the resistivity. The material of the core is then called alloy of iron (steel).
(iii) Hystersis loss : The alternating current flowing through the coils magnetises and demagneties the iron core again and again. Therefore, during each cycle of magnetisation, some energy is lost due to hysteresis. However, the loss of energy can be minimised by selecting the suitable of core, which has a narrow hysterisis loop. Therefore core of transformer is of soft iron. Now a days it is made of “Permalloy” (Fe-22%, Ni-78%).
(iv) Magnetic flux Leakage : Magnetic flux product in the primary winding is not completely linked with secondary becuase few magnetic field lines complete their path in air. To minimize this loss secondary winding is kept inside the primary winding.
(v) Humming losses : Due to the passage of alternating current, the core of the transformer starts vibrating and produces humming sound. Thus, some part (may be very small fraction) electircal energy is wasted in the form of humming sound produced by the vibrating core of the transformer.
