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July 13, 2020

Three phase induction motors employ a simple construction composed 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 where a rotating electro-magnetic field it developed by applying a three-stage 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 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 structure. They are more robust and can operate in any environmental condition

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

They are maintenance free motors unlike dc motors due to the lack 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 Machines meaning that the rotor does not switch at the precise same speed since the stator’s rotating magnetic field. Some difference in the rotor and stator rate is necessary to be able to develop the induction in to the rotor. The difference between the two is called the slip. Slip must be kept in a optimal range to ensure that the motor to operate efficiently. Roboteq AC Induction controllers can be configured to operate in another of three modes:

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

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

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

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