Tuesday, July 17, 2012


AC motor

An AC motor is an electric motor driven by an alternating current.

It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.

There are two main types of AC motors, depending on the type of rotor used. The first type is the induction motor, which runs slightly slower than the supply frequency. The magnetic field on the rotor of this motor is created by an induced current. The second type is the synchronous motor, which does not rely on induction and as a result, can rotate exactly at the supply frequency or a sub-multiple of the supply frequency.

A current is passed through the coil, generating a torque on the coil. Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave. It is called a synchronous motor.

One of the drawbacks of this kind of AC motor is the high current which must flow through the rotating contacts. In common AC motors the magnetic field is produced by an electromagnet powered by the same AC voltage as the motor coil. The coils which produce the magnetic field are sometimes referred to as the "stator", while the coils and the solid core which rotates is called the "armature". 


  • AC Motors Convert Electric Energy into Mechanical Energy
    • When a conductor is moving across a magnetic field a voltage is induced
    • If the conductor is part of a closed circuit there will be a current induced
    • In a motor, the induction principle is utilized in reverse
    • A live conductor is placed in a magnetic field
    • The conductor is influenced by a force which tries to move it through the magnetic field
  • The AC motor is made up of two parts
    • Stator  -The stationary section that contain the windings (magnetic field)
    • Rotor – The rotating section that contains the conductors.
Fig 6.2 The AC Motor principles operation

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