Two basic types of electric motors are designed to work with polyphase alternating current, synchronous motors and induction motors. The constant speed of a synchronous motor is profitable in certain devices, however, this type of motor can not be used in 200ydaaal applications where the mechanical load on the motor becomes higher, since if the motor reduces its speed when it is low charge and can be out of phase with the frequency of the current and stop. Synchronous motors can operate with a single-phase power source with the inclusion of suitable circuit elements to achieve a rotational magnetic field.
The synchronous motor is in essence a three-phase alternator that works the opposite and the field magnets cover a rotor and are excited by direct current, and the coils of the armature are divided into three parts and fed with three-phase alternating current. Modifying the three current waves in the armature causes a variable magnetic reaction with the poles of the field magnets, and causes the field to rotate at a constant speed, which is determined by the frequency of the current in the AC power line.