Difference between Induction Motor and Synchronous Motor

In this article, we will discuss the important differences between induction motor and synchronous motor (Induction Motor Vs Synchronous Motor).

An electric motor is an electromechanical energy conversion device that converts electrical energy into mechanical energy. There are several types of electric motors exist such as DC motors, AC motors, induction motors, synchronous motors, etc. However, the main function of a motor is to convert electrical energy into mechanical energy.

Definition of Induction Motor

An induction motor is a type of AC motor whose operation is based on the principle of electromagnetic induction. It is a type of asynchronous AC motor as its rotor rotates at a speed always less than synchronous speed (speed of rotating magnetic field).

An induction motor typically consists of two major parts namely the stator and the rotor. The stator is a stationary part while the rotor is a rotating part. In an induction motor, the stator carries the armature winding to which electrical energy is input, whereas the rotor carries a short-circuited rotor winding.

Since, for the operation of the induction motor, a continuous electromagnetic induction must take place in the induction motor. Therefore, the rotor of the induction motor cannot rotate at a synchronous speed.

Induction motors are the most widely used type of ac motor in industries. It is used for driving mechanical loads such as compressors, fans, conveyors, cranes, machinery, etc.

Definition of Synchronous Motor

As the name implies, a synchronous motor is a type of AC motor which runs at synchronous speed (i.e. speed of the rotating magnetic field). A synchronous motor is a constant-speed ac motor used to drive mechanical loads in industries.

Similar to any other electric motor, a synchronous motor also consists of two parts, i.e. stator and rotor. Stator carries the armature winding supplied from an ac supply, whereas the rotor carries the rotor winding, which is also excited from an external DC supply.

Therefore, a synchronous motor is a type of doubly excited machine. The rotor of the synchronous motor always runs at a constant speed or synchronous speed.

Generally, synchronous motors are used in industries to drive a mechanical load at a low and constant speed.

After discussing the basics of induction motor and synchronous motor individually. Now, let us understand the differences between them.

Differences between Induction Motor and Synchronous Motor

The following are the important differences between induction motor and synchronous motor:

• An induction motor is a type of asynchronous motor, while a synchronous motor is a synchronous machine.
• An induction motor is a singly-excited machine, while the synchronous motor is a type of doubly-excited machine.
• In an induction motor, the rotor runs at a speed less than the synchronous speed, while in a synchronous motor, the rotor runs at the synchronous speed.
• The induction motor is a self-starting motor, while the synchronous motor is not a self-starting motor.
• The speed of an induction motor changes with the change in load on the shaft, while the speed of a synchronous motor is independent of the load on the shaft.
• An induction motor has a lagging power factor only, while the synchronous motor can operate at a lagging, leading, or unity power factor.
• The induction motor requires relative motion between the stator magnetic field and the rotor, while the synchronous motor does not need the relative motion between the stator magnetic field and the rotor.
• Induction motors are simpler in construction, while synchronous motors are complex in construction.
• For the same power rating, induction motors are less efficient, while synchronous motors are comparatively more efficient.
• Induction motors are economical for driving speeds more than 600 RPM, while synchronous motors are more economical for driving speeds less than 300 RPM.
• The induction motor does not require excitation at the rotor, while the synchronous motor requires DC excitation at the rotor.
• In induction, motor slip varies from 0 to 1, while in synchronous motor slip is zero.
• The induction motor is considered a variable-speed motor, while the synchronous motor is considered a constant-speed motor.
• An induction motor is used to drive mechanical loads only, while a synchronous motor can be used to drive mechanical loads as well as for power factor correction.

Induction Motor Vs Synchronous Motor

The following table gives the important differences between induction motors and synchronous motors:

Induction Motor	Synchronous Motor
An induction motor is a type of asynchronous motor.	A synchronous motor is a synchronous motor.
An induction motor is a singly-excited machine.	A synchronous motor is a type of doubly-excited machine.
In an induction motor, the rotor runs at a speed less than synchronous speed.	In a synchronous motor, the rotor runs at the synchronous speed
The induction motor is a self-starting motor.	A synchronous motor is not a self-starting motor.
The speed of an induction motor changes with the change in load on the shaft.	The speed of a synchronous motor is independent of the load on the shaft.
An induction motor has a lagging power factor only.	Synchronous motors can operate at lagging, leading, or unity power factors.
The induction motor requires relative motion between the stator magnetic field and the rotor.	A synchronous motor does not need the relative motion between the stator magnetic field and the rotor.
Induction motors are simpler in construction.	Synchronous motors are complex in construction.
For the same power rating, induction motors are less efficient.	Synchronous motors are comparatively more efficient.
Induction motors are economical for driving speeds of more than 600 RPM.	Synchronous motors are more economical for driving speeds less than 300 RPM.
The induction motor does not require excitation at the rotor.	The synchronous motor requires DC excitation at the rotor.
In induction, motor slip varies from 0 to 1.	In a synchronous motor, the slip is zero.
The induction motor is considered a variable-speed motor.	A synchronous motor is considered a constant-speed motor.
The induction motor is used to drive mechanical loads only.	Synchronous motors can be used to drive mechanical loads as well as for power factor correction.

Hence, this is all about the key differences between induction motors and synchronous motors. In conclusion, the induction motor is one that operates at a speed slightly less than the synchronous speed, whereas the synchronous motor is one that operates at a speed equal to the synchronous speed.

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