Induction Motor Vs Synchronous Motor | Electronicsinfos

What is an Induction Motor?

An induction motor is an electric motor that operates on the principle of electromagnetic induction. When an alternating current (AC) is passed through the motor's stator windings, 

it creates a rotating magnetic field. This rotating magnetic field induces currents, known as eddy currents.

The rotor generates a magnetic field that interacts with the stator's magnetic field. The application of electric motors is vast. 

What is a Synchronous Motor?

A synchronous motor is an electric motor that operates at a constant speed. Synchronous motors operate based on the principle of synchronous speed, which is determined by the frequency of the AC power supply and the number of poles in the motor. 

• Synchronous Speed (rpm) = (120 x Frequency) / Number of Poles

Example 

For example, a four-pole motor operating on a 60 Hz supply has a synchronous speed of 1800 rpm (120 x 60 / 4).

Difference Between Induction Motor And Synchronous Motor

The key differences between induction motors and synchronous motors in their operating principles, speed control methods, starting torque characteristics, power factor, and efficiency including

Induction Motors 

1. The Principle of Induction Motor is Electromagnetic Induction.
2. The rotor rotates slightly lower than synchronous speed due to slip.
3. Speed is controlled by varying the frequency of the AC power supply or using variable frequency drives (VFDs).
4. These motors have Wound rotors with slip rings or a Squirrel cage rotor.
5. The rotor current is AC and is induced by magnetic induction.
6. These Motors run at less than synchronous speed. full load slip is about 4 %.
7. These motors take lagging power factor currents.
8. These motors have inherent high starting torque.
9. These motors start unaided.
10. These motors are used for variable speed and variable load drives.
11. For the same size, The motors are cheaper.
12. The Induction Motor requires only an AC supply.
13. Induction Motors are used in Pumps, cranes, hoists, elevators, compressors, conveyors etc.

Synchronous Motors 

1. These Motors have DC poles on the rotor energized by an excitation system.
2. The field current (Excitation current) can be changed to vary the power factor.
3. These Motors always run at a Synchronous Speed without Slip.
4. These Motors take different P.F. currents depending upon the excitation level.
5. These Motors do not have any inherent starting torque.
6. These motors have to be started by suitable means and brought to a synchronous speed and then synchronized.
7. These Motors are used for constant speed and constant load drives.
8. These motors are costly due to the additional cost of the excitation system.
9. It Requires Both Types of Supply(AC + Dc).
10. Synchronous Motors are used in Blowers, Fans, centrifugal pumps, reciprocating pumps, paper mils etc.

The choice between an induction motor and a synchronous motor depends on the needs. Induction motors are best suited for applications where varying speed is not an issue. 

Conclusion

In conclusion, choose an induction motor for variable speed applications with high starting torque requirements. Opt for a synchronous motor when precise speed control, high efficiency, and constant speed operation are necessary.

FAQs(Frequently Asked Questions)

What is the difference between an induction motor and a synchronous motor?

• Induction motors work on the principle of electromagnetic induction. where a rotating magnetic field is induced in the rotor, causing it to rotate. 
• Synchronous motors, on the other hand, operate at a constant speed that is synchronized with the frequency of the AC power supply.

Which motor is more efficient, induction or synchronous?

Synchronous motors are generally more efficient than induction motors because they do not have slip losses.

What are the applications of induction motors and synchronous motors?

• Induction motors are commonly used in household appliances, industrial fans, pumps, and conveyor systems. 
• Synchronous motors are used in applications where precise control of speed is required, such as in industrial processes, synchronous generators, and large machinery.

Do induction motors require external excitation like synchronous motors?

No, induction motors do not require external excitation. They operate based on the principle of induction and do not rely on a separate excitation source like synchronous motors.

Can synchronous motors operate at variable speeds?

Synchronous motors can operate at variable speeds using specialized control techniques such as variable frequency drives (VFDs) or electronic converters. 

What are the advantages of synchronous motors over induction motors?

Some advantages of synchronous motors include higher efficiency, power factor correction capabilities, better speed control, and suitability for applications requiring constant speed operation.

Are synchronous motors more expensive than induction motors?

Yes, synchronous motors are more expensive than induction motors due to their specialized design.

Which motor type is more suitable for high-torque applications?

Induction motors are often preferred for high-torque applications due to their ability to provide starting torque without the need for additional equipment like a starting winding or external excitation.

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