Constructional Difference :
Synchronous Motor :
We know that every electric motor gives mechanical energy ( rotation of shaft ) as the output when an electrical potential ( electrical energy ) is applied as the input ( to the input terminals ). Similarly, a synchronous motor is also an electric motor whose mechanical energy ( rotation of shaft ) developed will remains unchanged, i.e., the speed of rotation is constant and irrespective of the load.
The speed at which a synchronous motor rotates is known as synchronous speed. In a synchronous motor, armature winding is excited by a three-phase supply and a separate d.c. supply is given to the field winding. Hence it is also known as a doubly excited motor.
Induction Motor ( asynchronous motor ) :
An asynchronous motor is also an electric motor that doesn't rotate as the synchronous motor. i.e., there will be a variation in speed with respect to load on the motor. There are various types of induction motors depends upon the construction. An induction motor is a singly excited machine. It does not require any dc excitation as seen in a synchronous motor.
Induction motors can be of single-phase and three-phase. Here the supply is given to the field winding ( stator ), and the rotor ( armature ) rotates in magnetic flux produced by the field poles, by the principle of induction. Hence it is known as an "Induction Motor".
Difference Between Induction Motor and Synchronous Motor :
S.no. |
Synchronous Motor |
Induction Motor |
---|---|---|
1. |
It is not self-starting. |
It is self-starting. |
2. |
Construction is complicated. |
Construction is simple, particularly in case of cage motor. |
3. |
It runs at constant speed i.e., synchronous speed irrespective of the load. |
It can not run at synchronous speed. The speed decreases as the load increases. |
4. |
Speed control is not possible. |
Sped control is possible. |
5. |
It is doubly excited machine and requires dc excitation. |
It is singly excited machine and does not requires any dc excitation. |
6. |
It can operate with wide range of power factors both lagging and leading. |
It always operates at lagging power factor. |
7. |
It is used for supplying mechanical loads as well as for p.f. improvement. |
It is used for supplying mechanical loads only. |
8. |
It torque is less sensitive to change in supply voltage. |
It torque is more sensitive to change in supply voltage. |
9. |
Hunting starts as loads changes suddenly. |
Phenomenon of hunting is absent. |
10. |
It is very costiler and requires the maintenance. |
It is cheaper and almost maintenance free particularly is case of cage motors. |