AC motors

Synchronous motor: 

• AC motors can be divided into two main categories first one Synchronous motor  
Stator has axial slots which consist stator winding wound for a specific number of poles. Generally a 
• salient pole rotor is used on which rotor winding is mounted. Rotor winding is fed with a DC supply with the help of slip rings. A rotor with permanent magnets can also be used.

• Stator poles rotate at the synchronous speed (Ns) when fed with a three phase supply. The rotor is fed with a DC supply. The rotor needs to be rotated at a speed near to the synchronous speed during starting. If done so, the rotor poles get magnetically coupled with the rotating stator poles, and thus the rotor starts rotating at the synchronous speed.
• Synchronous motor always runs at a speed equal to its synchronous speed. 

          i.e. Actual speed = Synchronous speed or  N = Ns = 120f/P

SYNCHRONOUS MOTOR