Definition: AC motor is an electrical device which converts electrical energy into mechanical energy. The conversion of electrical energy to mechanical energy is through a coupling medium of magnetic flux. This magnetic flux is set-up in the air gap of AC Motor. Electrical energy supplied to the stator is first converted into magnetic energy in the air gap, which in turn is converted into mechanical energy. This is the reason, AC Motor is known as electromagnetic device.
As the name suggest, ac power is utilized in AC motor for conversion into mechanical energy at its shaft. The power supply may either be single phase or three phase depending upon the type of AC motor.
Classification of AC Motor:
Based on the working principle, there are mainly three types of AC motors: Induction Motor, Synchronous Motor and AC Commutator Motor.
An induction motor can further be of two types: Single Phase Induction Motor and Three Phase Induction Motor. This classification of induction motor is based on the type of power supply required for its operation. 1 phase AC supply is required for single phase induction motor whereas 3 phase AC supply is needed for three phase induction motor.
On the basis of construction, there are two types of induction motor: Squirrel cage Induction Motor and Slip Ring Induction Motor. Squirrel cage induction motor is most used motor in industries. Slip Ring Induction motor is used where speed control is required.
Synchronous motors are a three phase motors which rotates at synchronous speed (Ns = 120f/P rpm). These motors require separate DC source for excitation of field winding. With some constructional modification, this DC source requirement for field excitement can be eliminated. Permanent magnet Synchronous Motor (PMSM) is an example of this where permanent magnet is used as field poles.
Induction Motors have constant speed characteristics and low operating power factor. Therefore, AC commutator motors are used for wide rage speed control at around unity power factor. Single phase series motor, repulsion motor and Scharge motor are types of AC commutator motor.