Describe with neat sketch working of hysteresis motor.

Describe with neat sketch working of hysteresis motor.
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Answer :

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Working: When stator is energized with single phase ac supply, rotating magnetic field is produced because of starting (auxiliary) and main windings, which remain in circuit permanently. The rotor, which is hysteresis ring, cuts this flux, emf is induced and eddy currents start circulating in rotor as it is a shorted ring. Thus eddy current torque is developed along with the hysteresis torque in the rotor. Hysteresis torque in the rotor is developed because the rotor magnetic material has high hysteresis loss property and high retentivity. Now the rotor starts rotating initially as induction motor with speed somewhat less than synchronous speed and rotor pole axis lagging behind the axis of rotating stator field. When the speed of the rotor reaches near about the synchronous speed, then rotor poles are locked with stator field poles and then rotor starts rotating with synchronous speed. At the condition of synchronism, the relative motion between stator field and rotor field vanishes, hence no eddy current & torque. In this condition the rotor continues to rotate because of hysteresis torque. This torque is constant at all speeds and motor runs with perfect synchronous speed. Due to the principle of magnetic locking this motor either rotates at synchronous speed or not at all.

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