AC three-phase motors can have two types of rotors, the squirrel cage or short-circuit rotor, which is of the same type used in single-phase motors and the coiled rotor, which is not closed internally short and has its coils connected to the collector in which it is possible to connect a rheostat, which allows the regulation of the current circulating in the rotor. This provides a smooth starting and decreases the common current peak at motor starters.
Asynchronous AC three-phase induction electric motors usually work at a steady speed, which varies smoothly with the mechanical load applied to their axis. It is simple, strong, low cost, low maintenance need and therefore the most industrially used engine. Due to advances in electronics it is possible to control the speed of these motors with the aid of frequency inverters. In the stator of the asynchronous AC motor are housed three windings referring to the three phases and these three windings are mounted with a lag of 120º. From the stator winding, the wires for connecting the motor to the mains supply can be in the number of 3, 6, 9 or 12 points.