Induction motors are the most widely used AC motors. The field winding is generally wound into slots spaced around the iron stator to form magnetic poles. A revolving electric field is set up in the stator windings and induces currents in the rotor windings. The interaction between these two fields produces the torque to turn the motor. The motor's speed varies depending on the load.
Synchronous motors operate at a fixed speed regardless of the load.
The stator windings match those of the induction motor. The field source is provided either by direct current or by a permanent magnetic material. DC motors provide torque and speed control at a lower cost than AC units and are mechanically more complex. The pole field winding on the stator is composed of magnetic poles, each with many turns carrying a small current. The armature winding is placed on the rotor with the ends of each coil connected to opposite bars.