What is the Difference between Synchronous and Induction Motor?

Electric motors are used in almost every industry and in a wide range of applications. Electric motors are available in a wide range of sizes and types. These motors can be selected based on their functioning, voltage, and applications. Using the proper motor with high-quality parts and performing regular maintenance keeps your motor running smoothly and protects endpoint equipment from wear and power spikes.

There are two types of AC Motors: Synchronous AC Motor and Induction Motor. This article will teach you the major differences between the Synchronous and Induction Motor  in terms of excitation, starting mechanism, efficiency and applications etc.


Electric motor is a machine which converts electric energy into mechanical energy usually by employing electromagnetic phenomena. It works on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force whose magnitude is determined by F = BIl Newton and whose direction is determined by Fleming’s Left-hand Rule. 

The various types of electric motor differ in the ways in which the conductors and the field are arranged and also in the control that can be exercised over mechanical output torque, speed, and position. The following are the two main types of electric motors:

  • AC motors, which are powered by alternating current
  • DC motors, which are powered by direct current


An alternating current is required for the AC motor to rotate. Using electromagnetic induction, this motor transforms alternating current to mechanical power. Magnetic fields generated by coils wrapped around the output shaft provide energy to an AC motor. AC motors are efficient, long-lasting, quiet, and adaptable, making them a suitable option for a variety of power generation applications.

There are two types of AC Motors: Synchronous AC Motor and Induction Motor.

Synchronous Motor

Synchronus motor

A motor that converts an AC electrical power into mechanical power and operates only at the synchronous speed is the synchronous motor.The stator in this motor features axial slots with stator winding wound for a certain number of poles. A Salient Pole Rotor is defined by the rotor winding that is mounted on it. Slip rings are used to feed a DC supply to the rotor winding. It’s also possible to employ a rotor with permanent magnets.

Sychronous ac motor construction

A revolving field is created when power is applied to a synchronous motor. This field tries to drag the rotor along with it, but it is unable to rotate due to rotor inertia. As a result, it does not produces starting torque. As a result, the synchronous motor is not self-starting.

Induction or Asynchronous AC Motor

The machine which converts the AC electric power into mechanical power by using an electromagnetic induction phenomenon in called an induction motor. The induction motor classified into two types

  • Single phase induction motor
  • Three phase induction motors.

The armature winding in an induction machine functions as both the armature and field winding. The flux in the air gap is created when the stator windings are connected to an AC supply. The flux rotates at a constant rate known as synchronous speed. The stator and rotor windings are both affected by the rotational flux. As it never runs at synchronous speed, an induction motor is also known as an asynchronous motor. Ns = 120f/P, for example. Induction motors are the most extensively used motor in both household and commercial applications.

Incution AC motor con

The stator winding is wound for a certain number of poles in this case. A wrapped rotor or a squirrel cage rotor can be employed. The rotor bars of a squirrel cage rotor are permanently short-circuited with end rings. Since the windings in a wound rotor are permanently short-circuited, no slip rings are necessary. The current passes through the rotor winding and reacts with the rotating flux to produce torque when the rotor circuit is closed. The speed will vary depending on the torque.

Difference Between Synchronous Motor And Induction Motor

DescriptionThe electromagnetic motor which converts electrical energy into mechanical work at constant speed is called a ‘Synchronous Motor’.The electromagnetic motor which converts electrical energy into mechanical work at variable speed is called as a ‘Induction Motor’.
PrincipleThe synchronous motor works on the principle of the ‘Magnetic Locking’.The induction motor works on the principle of ‘Electromagnetic Induction’.
Type of ExcitationDoubly excited machine.Single excited machine.
Supply SystemIts armature winding is energized from an AC source and its field winding from a DC source.Its stator winding is energized from an AC source.
Motor SpeedSynchronous motor runs at the synchronous speed.Induction motor runs at the non-synchronous speed.
Starting MechanismIt is a non-self starting motor.It is self-starting the motor. (especially three-phase induction motor)
OperationOperated with lagging and leading power by changing its excitation.Operates only at a lagging power factor. At high loads the power factor becomes very poor.
EfficiencyMore efficient than an induction motor of the same output and voltage rating.Efficiency is lesser than that of the synchronous motor of the same output and the voltage rating.
Connected SupplyIt consists of two main parts- the stator and rotor.  
Stator connects with the three-phase AC supply and Rotor connects with the DC supply respectively.
Similarly, it also consists of two main parts- the stator and rotor.
The only Stator connects with the three-phase AC supply.
ConstructionThe construction of the synchronous motor is very difficult.The construction of the induction motor is relatively easy.
CostThis motor is costlier than the induction motor.This motor is cheaper than the synchronous motor.
Relative MotionRelative motion is not required in between the stator and rotor.Relative motion is required in between the stator and rotor.
Power FactorIt has unity or lagging or leading power factor.  Mostly it works on the unity power factor.It has only a lagging power factor.
Slip(magnetic field vs rotor speed)Zero slip (S=0) occurs in the synchronous motor.The different slip occurs in the induction motor.
UsageIt is used for power factor correction, constant speed load service, voltage regulation of transmission line, etc.It is mostly used in the industries.


We hope this blog helps you to understand the major difference between Synchronous and Induction AC motors. Visit our online site for more interesting articles

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