AC MotorAs in the DC motor case, a current is passed through the coil, generating a torqueon the coil. Since the current is alternating, the motor will run smoothly only at thefrequency of the sine wave. It is called a synchronous motor. More common istheinduction motor, where electric current is inducedin the rotating coils ratherthan supplied to them directly.
AC GeneratorThe turning of a coil in a magnetic field produces motional emfs in both sides of thecoil which add. Since the component of the velocity perpendicular to the magneticfield changes sinusoidally with the rotation, the generated voltage is sinusoidal or AC.This process can be described in terms of Faradays law when you see that therotation of the coil continually changes the magnetic flux through the coil andtherefore generates a voltage.
One of the drawbacks of this kind of AC motor is the high current which must flowthrough the rotating contacts. Sparking and heating at those contacts can waste energyand shorten the lifetime of the motor. In common AC motors the magnetic field isproduced by an electromagnet powered by the same AC voltage as the motor coil. Thecoils which produce the magnetic field are sometimes referred to as the "stator", whilethe coils and the solid core which rotates is called the "armature". In an AC motor themagnetic field is sinusoidally varying, just as the current in the coil varies. How Does an Electric Motor Work?
Motor Construction The StatorThe stator forms a hollow cylinder with coils of insulated wire inserted into slots ofthe stator core. The coils, plus the steel core form the electromagnets.
Motor Construction The Rotor There are two types of motor rotors: 1)The wound rotor 2)The squirrel cage The wound rotor has coils of wire wound in the slots of the rotor (Similar to generator coils). The “Squirrel cage” consists of bars of copper or aluminum electrically connected at each end with conducting rings.As the rotor rotates inside a magnetic field, it receiveselectromagnetic induction, then current flows and form the rotorelectromagnet.
Three Phase AC MotorIt has three pairs of electromagnets, connected to one of the three phases of the powersupply.It provides a lot higher power that what single phase motor can deliver.