Comparison of Synchronous and Induction Motor

Comparison of Synchronous and Induction Motor

Synchronous motor     

1. Construction is complicated        

2. Not self starting.       

3. Separate d.c. source is required for rotor excitation.

4. The speed is always synchronous irrespective of load.      

5. Speed control is not possible.      

6. As load increases, load angle increases, keeping speed constant as synchronous.

7. By changing excitation, the motor p.f. can be changed from lagging and leading.    

8. It can be used as synchronous condenser for p.f. improvement.  

9. Motor is sensitive to sudden load changes and hunting results.   

10. Motor is costly and requires frequent maintenance.

Induction motor

1. Construction is simpler, particularly in case of cage rotor.

2. Self starting.

3. Rotor gets excited by the induced e.m.f. So separate source is not necessary.

4. The speed is always less than synchronous but never synchronous.

5. Speed control possible though difficult.

6. As load increases, the speed keeps on decreasing.

7. It always operates at lagging p.f. and p.f. control is not possible.

8. It cannot be used as a synchronous condenser.

9. Phenomenon of hunting is absent.

10. Motor is cheap specially cage motors are maintenance free.

Review Question

1. Compare synchronous motor and induction motor.