An induction is an AC electric motor in which the electric current in the rotor needed to generate torque is got by electromagnetic induction from the magnetic field of thestator winding. An induction motor hence does not need mechanical commutation, separate-excitation or self-excitation for all or part of the energy transferred from stator to rotor, as in universal, DC and large synchronous motors. An induction motor's rotor can be wound or squirrel-cage .
Three-phase squirrel-cage induction motors are widely applied in industrial drives due to their rugged, reliable and economical feature. Single-phase induction motors are applied extensively for smaller loads, such as household appliances like fans. Traditionally they are applied in fixed-speed service, but induction motors are increasingly being applied with variable-frequency drives (VFDs) in variable-speed service. VFDs gives especially crucial energy savings chance for existing and prospective induction motors in variable-torque centrifugal fan, pump and compressor load applications. Squirrel cage induction motors are very widely applied in fixed-speed and variable-frequency drive (VFD) applications. Variable voltage and variable frequency drives are also applied in variable-speed service.
One of the most common electrical motor applied in most applications, as we all know, is induction motor,which has another name as asynchronous motor for the fact that it runs at a speed less than synchronous speed. In this case, we have to define what synchronous speed is. Synchronous speed is the speed of rotation of the magnetic field in a rotary machine and it is determined by the frequency and number poles of the machine. An induction motor always runs at a speed less than synchronous speed due to the fact that the rotating magnetic field which is generated in the stator will make flux in the rotor which will make the rotor to rotate, but because of the lagging of flux current in the rotor with flux current in the stator, the rotor fails to overpass its rotating magnetic field speed i.e. the synchronous speed. There are basically two types of induction motor that depends upon the input supply : single phase induction motor and three phase induction motor. Single phase induction motor does not have the function of self starting while three phase induction motordoes.