AC Motors Principle, Working and Types

 AC Motors

 The motor that converts the alternating current into mechanical power by using electromagnetic induction is called an AC motor. The stator and the rotor are the two most important parts of the AC motors. The stator is the stationary part of the motor, and the rotor is the rotating part of the motor.

Asynchronous Motors or Induction Motor:

  The most common form of motor which is used in marine life from pumping water up the overhead tank to  boiler feed pumps, these kinds of motors rule. These motors are very flexible to use and matches the load demand almost for everything

  In a DC motor, we give one supply to the stator and another to the rotor through brush arrangement. But in an induction motor, we give only one supply to the stator. As the name suggests it works on the principle of electromagnetic induction. When the stator windings are connected to an AC supply flux is produced in the air gap due to the flow of current in the coil. 

   The flux from the stator cuts the coil in the rotor. As the rotor coils are short-circuited, according to Faraday’s law of electromagnetic induction, the current will start flowing through the coil of the rotor. When the current through the rotor coils flows, another flux gets generated in the rotor. Now there are two fluxes, one is stator flux, and another is rotor flux. The rotor flux will be lagging in respect of the stator flux. Because of that, the rotor will feel a torque which will make the rotor rotate in the direction of the rotating magnetic field.

   Due to the lag between the flux current in the rotor and the flux current in the stator, the rotor will never reach its rotating magnetic field speed therefore Induction motors are referred to as ‘asynchronous motors’ because they operate at a speed less than their synchronous speed.


Synchronous Motors

  Its speed remains constant under varying loads, it is used for driving continuously-operating equipment at constant speed. 

 When supply is given to the synchronous motor, a revolving field is set up. This field tries to drag the rotor with it, but could not do so because of rotor inertia. Hence, no starting torque is produced. Thus, an inherently synchronous motor is not a self-starting motor.

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