What is an Asynchronous Motor : Construction & Its Working

In electrical machines like motors, we frequently get confused with the types of motors like a synchronous motor as well as an asynchronous motor with their applications. These motors are used in different applications due to reliability as well as robustness. As the name suggests, the name of this motor comes from the fact that the rotor in the motor runs asynchronously to a turning magnetic field. So, this article describes an overview of asynchronous motor, construction, working principle, etc.

What is Asynchronous Motor?

Definition: An electric motor that works with alternating current is known as the asynchronous motor. This motor mainly works on the induced current within the rotor from the rotary magnetic field of the stator. In this motor design, the movement of the rotor cannot be synchronized through the moving stator field. The rotating stator field of this motor can induce a current within the windings of the rotor. In turn, this current will generate a force to push the rotor in the direction of the stator. In this motor, as the rotor is not in phase with the stator, then the torque will be generated.

Asynchronous Motor
Asynchronous Motor

This is the most common type of motor. In particular, an asynchronous motor with 3-phase is used in the industry due to the reasons like it is a low cost, maintenance is easy and simple. The performance of this motor is good to compare with the single-phase motor. The main feature of this motor is, the speed cannot be changed. The operating speed of this motor mainly depends on the frequency supply as well as the no. of poles.

Construction of Asynchronous Motor

In this motor construction, the motor doesn’t include any magnets. In this motor design, the phases can be connected with the coils. So that the magnetic field can be generated. In this motor, the current flow within the rotor can be activated through an induced voltage from the rotating field. Once the magnetic field is applied to pass the rotor then the voltage will be induced at the rotor. Because the rotor’s magnetic field can be generated through the stator’s magnetic field. Basically, the magnetic field of the rotor runs asynchronously toward the magnetic field of the stator or with a delay in time. So the delay among the two magnetic fields can be known as ‘Slip’.

Construction of Asynchronous Motor
Construction of Asynchronous Motor

Asynchronous Motor Working

The working principle of this motor is almost the same as the synchronous type motor except for the external exciter. These motors also called induction motors, works on the electromagnetic induction principle, where the rotor in this motor doesn’t get any electric power through conduction as in the case of DC motors. These motors don’t have any external devices to stimulate the rotor within the motor. Thus, the speed of the rotor mainly depends on unstable magnetic induction.

The electromagnetic field which varies can cause the rotor to turn at a low-speed than the magnetic field of the stator. When the rotor’s speed, as well as the speed of the magnetic field within the stator, varies, then these motors are called asynchronous motors. The variation within the speed can be called as the slip.

Difference between Synchronous and Asynchronous Motor

The difference between synchronous and asynchronous motor is listed in the following table.

FunctionSynchronous Motor


Asynchronous Motor


DefinitionThis is one kind of machine where the speed of the rotor & the stator magnetic field’s speed is equivalent.

N= NS = 120f/P

This is one kind of machine where the rotor rotates at less speed compare with the synchronous speed.

N is less than NS

TypeTypes of synchronous are variable reluctance, brushless, hysteresis and switched reluctance.AC induction is also known as the asynchronous motor.
SlipThe slip value of this motor is zeroThe slip value of this motor is not equal to zero
CostIt is expensiveIt is less cost
EfficiencyHigh efficientLow efficient
SpeedThe motor speed does not rely on the disparity in the load.The motor speed reduces when the load increases.
Current supplyThe current supply can be given to the rotor in the motorThe rotor in this motor does not need any current.
Self StartingThis motor is not self-startingThis motor is self-starting
Torque effectOnce the applied voltage changes then it will not affect the torque of this motorOnce the applied voltage changes then it will affect the torque of this motor
Power factorThe power factor can be changed once the excitation is changed based on lagging, unity or leading.It works simply at a lagging power factor.
ApplicationsThese motors are applicable in industries, power stations, etc. This motor is also used as a voltage controllerThese motors are applicable in fans, centrifugal pumps, paper mills, blowers, lifts, compressors and textile mills, etc


The advantages of asynchronous motor include the following.

  • Less cost
  • Easy to maintain
  • Efficiency is high in partial-load operation
  • Appropriate for high revolving speeds, which permits high o/ps to be attained along with VECTOPOWER inverters


Most of the motors used in different applications in the world are asynchronous. The applications mainly include the following.

  • Centrifugal Pumps
  • Blowers
  • Fans
  • Conveyors
  • Compressors
  • Heavy Duty Cranes
  • Lifts
  • Lathe Machines
  • Paper Mills
  • Oil Mills
  • Textiles


1). Why asynchronous motor is also called as an induction motor?

The asynchronous motor depends on the induced current within the rotor from the rotary magnetic field in the stator.

2). what are the types of asynchronous motors?

They are single-phase and three-phase motors

3). what is the main feature of an asynchronous motor?

The main feature of this motor is the speed cannot vary.

4). what is the p.f(power factor) of an asynchronous motor?

This motor works simply at a lagging p.f.

Thus, this is all about an overview of an asynchronous motor. These motors are frequently used in 90% of the applications all over the world due to reasons like great robustness and reliability. These motors are used in different moving or rotating machines like lifts, fans, grinders, etc. Here is a question for you, what are the disadvantages of an asynchronous motor?

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