Three phase induction motors Induction Motor employ a simple construction made up of a stator covered with electromagnets, and a rotor made up of conductors shorted at each end, arranged as a “squirrel cage”. They work on the theory of induction in which a rotating electro-magnetic field it made by applying a three-phase current at the stators electromagnets. This in turn induces a current within the rotor’s conductors, which in turns generates rotor’s magnetic field that attempts to check out stator’s magnetic field, pulling the rotor into rotation.

Benefits of AC Induction Motors are:

Induction motors are simple and rugged in construction. They are more robust and can operate in any environmental condition

Induction motors are cheaper in expense because of simple rotor construction, absence of brushes, commutators, and slide rings

They are free of maintenance motors unlike dc motors because of the absence of brushes, commutators and slip rings

Induction motors can be operated in polluted and explosive environments as they do not have brushes that may cause sparks

AC Induction motors are Asynchronous Devices and therefore the rotor will not turn at the exact same speed because the stator’s rotating magnetic field. Some difference in the rotor and stator speed is necessary in order to generate 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 use effectively. Roboteq AC Induction controllers can be configured to operate in another of three modes:

Scallar (or Volts per Hertz): an Open loop mode in which a command causes a simultaneous, fixed-ratio Frequency and Voltage modify.

Controlled Slip: a Closed Loop speed where voltage and frequency are controlled in order to keep slip inside a narrow range while running at a preferred speed.

Field Oriented Control (Vector Drive): a Closed Loop Rate 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.