Actual Difference Between Synchronous Motor and Induction Motor

The actual difference between Synchronous Motor and Induction Motor is,

In the Induction motor, the flux is produced in the rotor for Mutual Induction between the stator and rotor coil. But in Synchronous motors, the flux is produced in the rotor for the applied external DC supply.

I have noticed there is much difference between Synchronous Motor and Induction Motor are given in books, blogs, etc. But in Interviews, the main actual difference is to be asked to you. So you should know the actual difference which is already given in the first paragraph.

Of course, we will discuss the other differences but Now we are going to discuss the actual differences in detail,

The Main Difference Between Synchronous Motor and Induction Motor:

If you understand the working of both motors, then you will understand the difference,

Synchronous Motor:

In a synchronous motor, there are two windings, one is the Stator winding and another is the rotor winding. We apply the main supply(230V for single phase or 440V for three-phase) to the stator winding and an external DC supply (24V or more) to the rotor winding.

click on the image to enlarge

The flux in the Stator Winding is produced by the main supply and the flux in the rotor winding is produced by the DC supply. The interaction of the stator flux and rotor flux creates a torque on the rotor of the motor which causes the motor to run.

So the conclusion is that the synchronous motor requires two sources(main AC supply to the stator and DC supply to the rotor) for its operation. It is the main basic concept of the operation of the synchronous motor.

Induction Motor:

Like the Synchronous motor, the Induction Motor also has two windings, one is stator winding and another is Rotor winding. The main power supply is applied to the stator winding. The rotor winding is kept short, there is no supply is given to the rotor winding of the Induction Motor. But we saw that DC supply is given to the rotor winding of the synchronous motor, this is the difference.

The flux in the stator winding is produced by the main power supply. And the flux in the rotor winding is produced for the mutual induction of both windings like transformer action.

click on the image to enlarge

The flux of the stator winding cuts the rotor winding conductor, hence an EMF is induced in the rotor winding. As the rotor winding is shorted, the current will flow through the rotor winding which produces the flux which is known as rotor flux.

Now the interaction of the Stator flux and Rotor flux creates a torque on the rotor which causes the motor to run.

So the conclusion is, that the induction motor requires only one source for its operation.

Other Comparisons Between Synchronous Motor and Induction Motor:

SL NO.	Synchronous Motor	Induction  Motor
1.	Synchronous Motor requires two sources for its operation.	Induction Motor requires only one source for its operation.
2.	The rotor of the synchronous motor always rotates at the synchronous speed which is why it is called a synchronous motor.	The rotor of the induction motor rotates at less than the synchronous speed which is why it is also called asynchronous motor.
3.	The synchronous motor works on the principle of Synchronization.	The Induction motor works on the principle of electromagnetic induction.
4.	In this motor Slip is Zero.	In this motor, the Slip varies from zero to one.
5.	The speed of the synchronous motor is independent of the changing of the load.	The speed of the induction motor depends on the changing of the load.
6.	The synchronous motor is not self-starting.	A three-phase induction motor is self-starting but a single-phase induction motor is not self-starting.
7.	An external Prime mover is used to start the synchronous motor.	A capacitor is used to start the single-phase induction motor.
8.	The synchronous motor can be used for power factor improvement purposes.	The Induction Motor cannot be used for power factor improvement purposes.
9.	Synchronous motors are more efficient than induction motors	Induction motors are less efficient than synchronous motors
10.	Synchronous motors are costlier than induction motors	Induction motors are less costlier than synchronous motors

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