Synchronous motors. A synchronous motor is one where the rotor normally rotates at the same quickness as the revolving field in the machine. The stator is comparable to that of an induction machine consisting of a cylindrical iron frame with windings, usually three-phase, positioned in slots around the inner periphery.
generally, synchronous motors are used for Auto Chain applications where precise and continuous speed is required. Low power applications of the motors include positioning devices. These are also applied in robot actuators. Ball mills, clocks, record participant turntables also make use of synchronous motors.
The principle of procedure of a synchronous electric motor can be understood by taking into consideration the stator windings to be connected to a three-phase alternating-current supply. The result of the stator current is usually to establish a magnetic field rotating at 120 f/p revolutions each and every minute for a frequency of f hertz and for p poles. A direct current in a p-pole field winding on the rotor may also produce a magnetic field rotating at rotor rate. If the rotor acceleration is made add up to that of the stator field and there is no load torque, both of these magnetic fields will tend to align with 
one another. As mechanical load is used, the rotor slips back numerous degrees with respect to the rotating field of the stator, developing torque and ongoing to become drawn around by this rotating field. The position between the fields boosts as load torque is usually increased. The maximum available torque is accomplished when the angle by which the rotor field lags the stator field is definitely 90°. App of more load torque will stall the motor.
One advantage of the synchronous electric motor is that the magnetic field of the device can be produced by the direct current in the field winding, so that the stator windings need to provide just a power component of current in stage with the applied stator voltage-i.e., the engine can operate at unity power factor. This condition minimizes the losses and heating system in the stator windings.