Difference between Synchronous Motor and Induction Motor

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A motor in general is an electrical machine that converts electrical energy into mechanical energy. Electric motors can either be DC Motors or AC Motors, depending on the type of power supply that is supplied as its input.

AC motors are further classified into two types&#;

• Asynchronous or Induction Motor
• Synchronous Motor

A synchronous motor always runs at synchronous speed, while an induction motor runs at a speed less than the synchronous speed.

Read through this article to find out more about synchronous motors and induction motors and how they are different from each other.

What is a Synchronous Motor?

A synchronous motor is a type of AC motor in which the rotor rotates at a synchronous speed at all loads, provided that the load on the motor does not exceed the limiting value. If the load on the shaft of a synchronous motor exceeds the limiting value, then the motor comes to rest and the average torque developed by it becomes zero.

A synchronous motor has a stator and a rotor. The stator consists of a 3-phase armature winding and receives power from a balanced 3- phase supply, while the rotor has a set of salient poles excited by direct current to produce alternate N and S poles. In case of a synchronous motor, the stator is wound for the same number of poles as the rotor poles.

What is an Induction Motor?

An induction motor is a type of AC motor in which the rotor rotates at a speed slightly less than the synchronous speed. Let's see how an induction motor works.

• An induction motor consists of a stator and a rotor. The stator carries a 3-phase winding, while the rotor carries a short-circuited winding.

• When the stator winding is energized from a 3-phase supply, a rotating magnetic field is produced which rotates around the stator.

• This rotating magnetic field passes through the air-gap and cuts the rotor conductors, which are stationary. Therefore, due to relative speed between the rotating magnetic field and the stationary rotor conductors, an EMF is induced in the rotor conductors.

• As the rotor circuit is short-circuited, currents start flowing in the rotor conductors.

• The current carrying rotor conductor are placed in the magnetic field produced by the stator winding. As a result, a torque develops on the rotor conductors and the sum of the torque on all the rotor conductors, rotates the rotor in the same direction as the rotating magnetic field but at a speed slightly less than the synchronous speed.

An induction motor cannot run at synchronous speed. If it runs at synchronous speed, there would be no cutting of the flux by the rotor conductors and there would be no induced EMF, no current and no torque. Therefore, the rotor of the induction motor rotates at a speed slightly less than the synchronous speed. For this reason, an induction motor is also known as an asynchronous motor.

Difference between Synchronous Motor and Induction Motor

The following table highlights the major points that differentiate a Synchronous Motor from an Induction Motor &#;

KeySynchronous MotorInduction MotorType of MachineA synchronous motor is a doubly excitation machine, i.e., its armature winding is connected to an AC source and its field winding is excited from a DC source.An induction motor is a singly excited machine, that is, its stator winding is energized from an AC source.SpeedIts speed is independent of the load.Its speed decreases with the increase in load.StartingIt is not self-starting. It requires external means for starting.Induction motor has self-starting torque.EfficiencyA synchronous motor is more efficient than induction motor of the same rating.The efficiency of an induction motor is lesser than that of a synchronous motor of same rating.Power FactorA synchronous motor can operate under a wide range of power factors, both lagging and leading.
The power factor of a synchronous motor can be changed by changing its excitation.
An induction motor operates at only lagging power factor.
The power factor of induction motor cannot be controlled. It becomes very poor (lagging) at high loads.
Relative MotionNo relative motion between the stator rotating magnetic field (RMF) and the rotor is required for the operation of a synchronous motor.For the operation of an induction motor, there must be a relative motion between the stator RMF and the rotor.Cost-effectivenessFor the same rating, a synchronous motor is expensive than an induction motor.An induction motor is cheaper than a synchronous motor.ConstructionA synchronous motor has complicated construction.An induction motor have simple construction than a synchronous motor.Starting TorqueA synchronous motor has high starting torque as compared to an induction motor.An induction motor has less starting torque.RPMSynchronous motors are economical for speeds below 300 RPM.The induction motors are economical for speeds above 600 RPM.ExcitationSynchronous motors require DC excitation at the rotor.Induction motors do not require excitation for the rotor.ApplicationsDriving mechanical loads at constant speed, power factor correction of electrical systems, etc.Induction motors are used for driving mechanical loads only.

Conclusion

The most important point that you should note here is that the rotors of a Synchronous motor rotates at a synchronous speed, while the rotors in an Asynchronous motor rotates at a speed slightly less than the synchronous speed.

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Understanding The Difference

While induction motors are found in water pumps, various kitchen appliances, air conditioners, automobiles, industrial machinery such as compressors, and others, synchronous motors are used in applications requiring constant and precise speed. There are also different types of synchronous motors.

Both motors are prominent in the construction industry for several applications. With that said, if you aren&#;t certain if you need a synchronous motor or an induction motor, we delve into the differences between these two motors in this article.

The Constructional Differences

When it comes to the synchronous motor, the stator consists of axial slots that consist of stator winding components for a particular number of poles. More often than not, a salient pole rotor is used for rotor winding. The rotor winding is fed by a DC power source via slip rings. Alternatively, a rotor with permanent magnets can also be used.

On the other hand, an induction motor also uses similar stator winding principles. However, a wound rotor or squirrel cage rotor can be used for an induction motor. When a squirrel cage rotor is used, the rotor bars are short-circuited with end rings permanently. In the case of wound rotors, slip rings are not required either as windings are also permanently short-circuited.

Working Differences

When fed with a three-phase supply, the stator poles of a synchronous motor will run at a speed that is equal to the synchronous speed. A DC power source must feed the rotor. When starting, the rotor is rotated at speed close to the synchronous speed, which magnetically couples the rotating stator poles. As a result, the rotor inevitably rotates at a synchronous speed.

But when it comes to the induction motor, a rotating magnetic field is produced when the stator is fed with a two or three-phase AC supply power source. The relative speed difference between the rotor and the stators rotating magnetic field will induce a current in the conductors of the rotor.

Other Differences

Synchronous motors need an additional power source to power rotor winding, while induction motors do not require any other power source.

Furthermore, synchronous motors require slip rings and brushes, while induction motors don&#;t. However, synchronous motors are the more efficient option, although they are typically more pricey. Even though induction motors are more budget-friendly, it&#;s never best to make a decision based on this factor alone.

More often than not, synchronous motors are a suitable option for various applications both around the home and in construction and other industries. These motors are used in analogue electric clocks, timers, and so much more. Due to their constant precision capabilities, they are often an excellent choice despite the higher price.

Whether you need synchronous motors, induction motors, or a mix of both for your construction business, it is crucial to know the advantages and disadvantages of each motor. Functioning in the construction industry and achieving success is relatively complex, and you will need to scale your business before you start investing in motors and other essentials you need. Scaling your business is the best way to set the stage for your success.

 

Contact us to discuss your requirements of Asynchronous Motor Vs Induction Motor. Our experienced sales team can help you identify the options that best suit your needs.