Question

Explain hysteresis loss, eddy current loss and skin effect limitations with reference to magnetic material.

Answer 1

Hysteresis loss:

Hysteresis loss is a loss which occurs due to the friction of magnetic domain due to the change in magnetic field in ferromagnetic material like iron. Hysteresis loss causes power loss and heat and insulation damage. The figure shows the hysteresis loop. if the loop is fat then hysteresis losses will be more and if the hysteresis loop is thin then hysteresis losses will be less. If the coercive force is high hysteresis loop will be fat and if the coercive force is low hysteresis loop will be thin. Hysteresis loss reduces the efficiency. Hysteresis loss cannot be completely removed but it can be reduced by choosing the material with less hysteresis loop area. Because less hysteresis loop area material will have low hysteresis loss.

Hysteresis loss in transformer is given by,

W_h = K_h f (B_m)^1.6 watts

Eddy current loss:

Eddy current also increases heat in the circuit. The loss due to eddy current is known as eddy current loss. Eddy current is caused due to the alternating current which induced emf and that induced emf produce current this current is called eddy current. 

Suppose a coil is wound on a core. An alternating current is applied to the coil. This alternating current to the coil will produce alternating flux. Now according to Faraday's law of electromagnetic induction, this changing flux will generate induced emf in the core. This induced emf will cause current to flow in the core. This flow of current is called eddy current and the losses due to eddy current are called eddy current loss. Eddy current causes I²R losses means heat. If there is a solid core with less resistance then eddy current will be high. Eddy current reduces the efficiency. Complete removal of eddy current is not possible but it can be reduced.

Eddy current can be reduced by using laminated core and by using the material with the high resistivity magnetic material. High resistivity magnetic material like silicon.

Eddy current loss in transformer is given by,

W_e=K_ef²K_f²B_m²watts

Skin effect limitations: