The synchronous motors have a squirrel cage in the rotor, with the function of accelerating the machine in the starting, Gates B116 Hi-Power II Belts since the starting of the synchronous machine is asynchronous, that is, in the starting the performance of the synchronous motor is the same of an asynchronous induction motor.
Usually the principle is the same as the induction induction motor, where the rotating field produced by the three-phase stator supply induces current in the rotor cage bars, first at rest or at maximum slip situation.
The current circulating in the rotor bars in turn will produce a field that interacts with the rotating field of the stator, where the result is the accelerating torque in the rotor, which takes the machine out of inertia. As the rotor accelerates, tending to follow the rotational speed of the rotating field, the induced current in the rotor reduces and the interaction between the field produced by the rotor cage bars and the rotating field also decreases, causing the sliding to go weakening. And near the synchronous speed the field winding in the rotor of the synchronous motor is energized, forming the north and south rotor poles.