Synchronous motors. A synchronous engine is one in which the rotor normally rotates at the same acceleration as the revolving field in the device. The stator is similar to that of an induction machine comprising a cylindrical iron frame with windings, usually three-phase, situated in slots around the inner periphery.
generally, synchronous Transmission Chain motors are used for applications where precise and constant speed is required. Low power applications of the motors include positioning machines. These are also used in robot actuators. Ball mills, clocks, record participant turntables also make use of synchronous motors.
The principle of operation of a synchronous engine could be understood by considering the stator windings to be linked to a three-phase alternating-current supply. The result of the stator current is definitely to establish a magnetic field rotating at 120 f/p revolutions per minute for a frequency of f hertz and for p poles. A primary current in a p-pole field winding on the rotor may also create a magnetic field rotating at rotor velocity. If the rotor velocity is made equal to that of the stator field and there is no load torque, these two magnetic fields will have a tendency to align with each other. As mechanical load is usually used, the rotor slips back a number of degrees with respect to the rotating field of the stator, developing torque and continuing to be drawn around by this rotating field. The angle between the fields boosts as load torque is increased. The utmost available torque is accomplished when the angle by which the rotor field lags the stator field is 90°. Software of more load torque will stall the motor.

One advantage of the synchronous engine is definitely that the magnetic field of the machine can be produced by the direct current in the field winding, so that the stator windings have to provide just a power element of current in phase with the applied stator voltage-i.e., the electric motor can operate at unity power element. This problem minimizes the losses and heating in the stator windings.