Electrical Engineering ⇒ Topic : Hysteresis Loss

Hysteresis loss

Hysteresis loss occurs due to the B-H magnetization curve which swings to positive and negative maximum B_max before returning to zero. Ideally the energy absorbed during the positive swing should be returned to the source during reversal of the magnetizing cycle. But in reality there is only a partial return to source, the rest being dissipated as heat

                                                                           ................... (1)

where V is volume of core material, f is frequency of variation of H in Hz.

The value of n is between 1.5 and 2.5 (1.5 ≤ n ≤ 2.5 ) but mostly it is 1.6

Hysteresis Loss

When a magnetic material is subjected to a cycle of magnetisation (i.e. it is magnetised first in one direction and then in the other), an energy loss takes place due to the *molecular friction in the material. That is, the domains (or molecular magnets) of the material resist being turned first in one direction and then in the other. Energy is thus expended in the material in overcoming this opposition.This loss is in the form of heat and is called hysteresis loss. Hysteresis loss is present in all those electrical machines whose iron parts are subjected to cycles of magnetisation. The obvious effect of hysteresis loss is the rise of temperature of the machine.

• Transformers and most electric motors operate on alternating current. In such devices, the flux in the iron changes continuously, both in value and direction. Hence hysteresis loss occurs in such machines.
• Hysteresis loss also occurs when an iron part rotates in a constant magnetic field e.g. d.c. machines.