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July 13, 2020

Three phase induction motors have a very simple construction made up of a stator covered 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 Induction in Motor 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 produces rotor’s magnetic field that attempts to follow 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 virtually any environmental condition

Induction motors are cheaper in cost due to simple rotor construction, absence of brushes, commutators, and slip 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 do not have brushes which can cause sparks

AC Induction motors are Asynchronous Machines and therefore the rotor will not convert at the specific same speed since the stator’s rotating magnetic field. Some difference in the rotor and stator acceleration 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 to ensure that the motor to use efficiently. Roboteq AC Induction controllers can be configured to operate in one of three modes:

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

Controlled Slip: a Shut Loop speed where voltage and frequency are managed to keep slip within a narrow range while operating at a preferred speed.

Field Oriented Control (Vector Drive): a Closed Loop Acceleration and Torque control that works by optimizing the rotating field of the stator vs. this of the induced field in the rotor.

Find this video from Learning Engineering for a visual illustration on how AC Induction Motors are constructed and work.