Synchronous motors. A synchronous electric motor is one where the rotor normally rotates at the same rate as the revolving field in the machine. The Drive Chain stator is comparable to that of an induction machine consisting of a cylindrical iron framework with windings, generally three-phase, located in slots around the internal periphery.
usually, synchronous motors are used for applications where precise and continuous speed is required. Low power applications of the motors include positioning devices. These are also used in robot actuators. Ball mills, clocks, record player turntables also utilize synchronous motors.
The principle 
of operation of a synchronous electric motor can be understood by considering the stator windings to be connected to a three-phase alternating-current supply. The effect of the stator current can be to establish a magnetic field rotating at 120 f/p revolutions per minute for a frequency of f hertz and for p poles. A direct current in a p-pole field winding on the rotor will also create a magnetic field rotating at rotor swiftness. If the rotor rate is made equal to that of the stator field and there is absolutely no load torque, these two magnetic fields will tend to align with one another. As mechanical load is definitely applied, the rotor slips back again several degrees with regards to the rotating field of the stator, developing torque and continuing to end up being drawn around by this rotating field. The position between the fields increases as load torque is usually increased. The utmost available torque is attained when the angle by which the rotor field lags the stator field is certainly 90°. Application of more load torque will stall the electric motor.
One advantage of the synchronous electric motor is definitely that the magnetic field of the machine can be produced by the immediate current in the field winding, so that the stator windings need to provide just a power component of current in phase with the applied stator voltage-i.e., the motor can operate at unity power factor. This problem minimizes the losses and heating system in the stator windings.