Three phase induction motors employ a simple construction made up of a stator protected with electromagnets, and a rotor composed of conductors shorted at each end, arranged as a “squirrel cage”. They work on the principle of induction in which a rotating electro-magnetic field it developed through the use of a three-phase current at the stators electromagnets. Therefore induces a current in the rotor’s conductors, which in turns creates rotor’s magnetic field that attempts to check out stator’s magnetic field, pulling the rotor into rotation.
Great things about AC Induction Motors are:
Induction motors are simple and rugged in construction. They are better Induction in Motor quality and can operate in any environmental condition
Induction motors are cheaper in cost because of simple rotor construction, absence of brushes, commutators, and slide rings
They are maintenance free motors unlike dc motors because of the absence of brushes, commutators and slip rings
Induction motors could be operated in polluted and explosive conditions as they don’t have brushes which can cause sparks
AC Induction motors are Asynchronous Devices meaning that the rotor will not turn at the exact same speed as the stator’s rotating magnetic field. Some difference in the rotor and stator velocity is necessary to be able to develop the induction into the rotor. The difference between the two is called the slip. Slip should be kept in a optimal range in order for the motor to operate effectively. Roboteq AC Induction controllers could be configured to operate in one of three modes:
Scallar (or Volts per Hertz): an Open loop mode where a order causes a simultaneous, fixed-ratio Frequency and Voltage alter.
Controlled Slip: a Shut Loop speed where voltage and frequency are managed to keep slip inside a narrow range while working at a preferred speed.
Field Oriented Control (Vector Drive): a Closed Loop Velocity and Torque control that functions by optimizing the rotating field of the stator vs. this of the induced field in the rotor.
Discover this video from Learning Engineering for a visual illustration about how AC Induction Motors are constructed and function.