Three phase induction motors have a very 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 focus on the principle of induction where a rotating electro-magnetic field it produced by applying a three-phase current at the stators electromagnets. This in turn induces a current within the rotor’s conductors, which in turns produces rotor’s magnetic field that tries to check out stator’s magnetic field, pulling the rotor into rotation.
Great things about AC Induction Motors are:
Induction motors are basic and rugged in structure. They are better quality and can operate in any environmental condition
Induction motors are cheaper in expense due to simple rotor construction, lack of brushes, commutators, and slip rings
They are maintenance free motors unlike dc motors due to the absence of brushes, commutators and slip rings
Induction motors can be operated in polluted and explosive environments as they do not have Induction Motor china brushes that may cause sparks
AC Induction motors are Asynchronous Devices and therefore the rotor will not convert at the specific same speed as the stator’s rotating magnetic field. Some difference in the rotor and stator velocity is necessary to be able to make the induction in to the rotor. The difference between the two is called the slip. Slip should be kept in a optimal range to ensure that the motor to use efficiently. Roboteq AC Induction controllers can be configured to operate in another of three modes:
Scallar (or Volts per Hertz): an Open up loop mode where a control causes a simultaneous, fixed-ratio Frequency and Voltage modify.
Controlled Slip: a Shut Loop speed where voltage and frequency are controlled in order to keep slip within a narrow range while working at a desired speed.
Field Oriented Control (Vector Drive): a Closed Loop Speed and Torque control that works by optimizing the rotating field of the stator vs. this of the induced field in the rotor.
Observe this video from Learning Engineering for a visual illustration about how AC Induction Motors are constructed and work.