Comparison between synchronous and induction motor

    Synchronous Motor

·  It has got no self-starting torque and some external means is required for its starting.
·     Its average speed is constant and independent of load
·     It can be operated under a wide range of power factor, both lagging and leading.
·       It required the dc excitation so it is a doubly excited machine,.
       No speed control is possible.
·     It’s used for supplying mechanical load as well as for power factor improvement.
  Its torque is less sensitive to change in supply voltage.
·       Breakdown torque is proportional to the supply voltage.
·       It is more complicated and cost more comparatively.

However, synchronous motors with speeds below 500 rpm and rating exceeding about 40 kw or with medium speed from 500 to 1, 00 rpm and rating exceeding about 500 kw cost less than induction motors 

Induction Motor:-

1. It has got self-starting torque and no special means is required for its starting.
2. Its speed falls with the increase in load and less than synchronous speed   
3.  It operate at only lagging power factor, which becomes very poor at light loads.Its requires no dc excitation so it’s a singly excited machine  
4. Its torque is more sensitive to change in supply voltage.Breakdown torque is proportional to the square of the supply voltage. 
5. It is more simple and cost less than Synchronous motor