SOLUTION

Working of Hysteresis Motor

The operation of the hysteresis motor depends on the permanently magnetized rotor which provides continuously revolving magnetic flux. It usually consists of the following components:

(a) The stator is wound with main and auxiliary windings. Usually, the auxiliary winding is connected in series with a permanent capacitor for the split-phase operation.

(b) The rotor is a smooth solid cylinder of hardened high-retentivity steel whose hysteresis loss is very high. It does not contain any winding.

• The rotating magnetic field produced by phase-splitting induces eddy currents in the steel of the rotor.
• High-retentivity steel produces a high hysteresis loss, thus consuming an appreciable amount of energy from the rotating field when the reversal of flux direction in the rotor takes place.
• Simultaneously, the rotor begins to rotate on account of the magnetic field set up by the eddy currents in the rotor.
• A high starting torque is developed as a result of high rotor resistance which is proportional to hysteresis loss.
• As the rotor approaches synchronous speed, the frequency of flux reversals in the rotor decreases, and the rotor becomes permanently magnetized in one direction as a result of the high retentivity of the steel rotor.
• The rotor revolves at synchronous speed because the rotor poles magnetically lock up with the revolving stator poles of opposite polarity.