Electrical Projects Motors run by alternating current operate on the same fundamental principle as those run by direct current—motion is produced because of the opposition of magnetic fields created by current flowing through wires. The magnetic field may be stationary, in which case it is called the stator; the armature rotates and is called the rotor. Conversely, the armature may be stationary, and called the stator; and the magnetic field rotated and called the rotor.

AC motors are similar to a dc motor, except that because the current through the rotor is alternating, slip rings are used and no commutator is required. In the example shown, a permanent-magnetic field is used, and motion is created by the opposition of the magnetic field created by current flowing in the rotor to the permanent magnetic field. As the rotor turns within the magnetic field, the current alternates to the opposite direction, and the new magnetic field also acts against the permanent-magnetic field to keep the rotor spinning.

Ac motors are generally classified as single-phase, polyphase, and synchronous, but most motors used in small home appliances are of the single-phase type.


Single-Phase AC Motors. Single-phase ac motors use only one phase of alternating current. A polyphase motor uses more than one phase of ac, and the difference between the phase is enough to start the motor and keep it running. But while single-phase motors run once started, there are several different methods used to get them to start.




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August 20, 2008