Difference Between Synchronous Motor And Induction Motor – A Comprehensive Guide

synchronous motor vs. induction motor

Many of us have an induction motor in our homes and probably use it daily. But induction motors are not the only motor option out there. There are synchronous motors that can often do a better job at running your equipment. This blog will discuss the differences between induction and synchronous motors, their work, and which motor is right for you.

What is a Synchronous Motor?

A synchronous motor is an electric motor designed to rotate at the same speed as its stator’s rotating magnetic field, also known as synchronous speed.

A synchronous motor’s rotor revolves around its stator, producing power without rotation. This makes synchronous motors energy-efficient and perfect for power generation, automation, and healthcare applications.

What is an Induction Motor?

An induction motor is often used in high-power demands and high-frequency rotor speed applications. 

In this motor, power is supplied by induction from a rotating magnetic field generated by the stator winding. The rotor sits inside the stator, creating magnetic field lines to induce a current in the rotor winding. We can manufacture induction motor cores for industrial applications.

induction motor

12 Key Differences Between Induction motor and Synchronous Motor

Synchronous MotorInduction Motor
Type of MachineA synchronous motor is an AC motor, a double excitation machine.While an induction motor is also an AC motor, a singly excited machine.
SpeedThe speed of a synchronous motor is constant.The speed of an induction motor varies depending on the load.
EfficiencyA synchronous motor operates at maximum efficiency when it runs at its rated speed,while an induction motor operates at the most efficiency when it runs slightly below its rated speed.
StartingA synchronous motor has to be started with an external auxiliary power source.Whereas an induction motor can self-start by itself.
Power FactorThe power factor in a synchronous motor is either lagging or unity and can be adjusted within these ranges as per needs,whereas that of an induction machine remains lag by default and cannot be changed.
Excitation SystemSynchronous motors require external excitation for operation.No external excitation system is needed for induction motors.
Relative MotionIn the case of the synchronous machine, the rotor rotates concerning the stator winding.No relative motion like sliding or slipping in the case of induction machines.
CostA synchronous machine costs more than an induction machine owing to its complexity and comparatively higher manufacturing cost.Induction motors, on the other hand, are cheaper to produce, implement, maintain, and repair.
ConstructionIt has salient features on its rotors, such as salient poles or nonsalient poles.It has squirrel cage rotors without any winding slots.
Starting TorqueIt remains almost constant irrespective of load variations.It falls with increased loads due to lower slippage for light loads.
RPMruns from 150 to 1800 rpmruns at less than 1500 rpm.
ApplicationsDriving mechanical loads constantly, power factor correction of electrical systems, etc.Driving mechanical loads only

Type of Machine

A synchronous motor is an AC motor, while an induction motor is also an AC motor but operates differently.

Speed

The speed of a synchronous motor is constant, while the speed of an induction motor varies depending on the load.

Efficiency

Synchronous motors have higher efficiency than induction motors, especially at lower speeds and power factors.

Induction motors, on the other hand, have rotor losses that reduce their overall efficiency. Synchronous motors power their stator while induction motors power their rotor, inducing current and causing torque.

Asynchronous induction motors create slip, which increases torque but reduces efficiency. In synchronous motors, current flows continuously in one direction, thus requiring less power input.

This is due to the speed-torque characteristics of the synchronous motor being constant over a range of speed and voltage settings. 

A synchronous motor provides higher efficiency than an induction motor at lower speed and power factor values.

Starting

Synchronous motors typically start with cage winding embedded in the pole faces to give an induction-motor torque when the stator is energized. The motor is started with full or reduced stator voltage and brought up to about synchronous speed, usually with the field winding short-circuited to protect it from excessive induced voltage.

Asynchronous motors can start when they supply power to the stator, eliminating the need for a power source to excite or start the rotor.

These motors are typically more power-efficient than synchronous motors and are, therefore, widely used in applications where speed accuracy is of primary importance.

Power Factor

The power factor of a synchronous motor can be adjusted within a range of lagging to unity, while the power factor of an induction machine remains lag by default and cannot be changed. This allows synchronous motors to adjust their power factor depending on the user’s needs, whereas induction motors are stuck with lagging power factors.

Excitation System

Synchronous motors require external excitation for operation. However, no external excitation system is needed for induction motors.

Synchronous motors require an external excitation system to be operational, whereas induction motors do not need any external excitation systems.

This difference affects the ease of operation for both motor types; synchronous motors may require more time and effort, but they can offer greater control than induction motors.

Relative Motion

Synchronous machines have a rotor that rotates in synchronization with the field, while induction machines rely on the principle of electromagnetic induction to produce relative motion between the stator and rotor.

Synchronous motors are used in applications where precise speed control is required, as they can precisely adjust their operating speed to match the frequency of an alternating current supply. This makes them useful in applications such as AC power generators, high-speed printing presses, and robotic systems.

On the other hand, induction motors provide reliable operation at low cost and low maintenance requirements; they are used in most industrial processes, such as fans and pumps.

Cost

no relative motion like sliding or slipping in the case of induction machines. Due to the complexity involved in their production and operation. Induction motors, on the other hand, are cheaper to produce, implement, maintain, and repair.

Synchronous motors require an external excitation system which adds additional costs and may make it more expensive than an equivalent induction motor.

Additionally, synchronous motors have more parts that must be constructed and assembled.

On the other hand, due to their simpler design and single-phase winding structure, induction motors are usually cheaper than synchronous machines.

However, compared with synchronous machines, induction motors usually have a lower power factor and less efficient performance.

Construction

Synchronous machines have salient features on their rotors, such as salient poles or nonsalient poles, which enable them to produce a magnetic field directly due to current passing through the rotor coil, thus resulting in a rotating magnetic field inside the stator coils hence generating torque.

construction of synchronous motor

construction of synchronous motor

On the other hand, Induction motors have squirrel cage rotors without any winding slots, so they don’t possess any way to generate a magnetic field as such hence making use of induced currents from the stator only, which results in a rotating Magnetic Field, thereby producing torque in the rotation direction.

Starting Torque

Starting torque for synchronous motors remains almost constant irrespective of load variations. However, induction motors starting torque falls with an increase in loads due to lower slippage present for light loads & rises sharply with an increase in loads due to higher slippage occurring from high load cases.

RPM

The speed of synchronous motors is constant, while the speed of induction motors varies depending on the load.

The speed of a synchronous motor can be controlled with its excitation system, while the speed of an induction motor cannot be adjusted but only vary depending on the load applied.

Applications

Synchronous motors are generally used where very precise control over speed/torque is required, like paper mills & compressors, and so on. However, induction motors are widely used where variable speeds are needed & also employed in applications like pumps, fans, elevators, compressors, etc.

Deciding which type is right for your needs?

Consider the speed, power, size, and output when choosing a motor. A thorough analysis of each factor can help you determine which motor is right for your application.

Consider factors such as rotor speed, power rating, stator voltage, and power factor of induction motors. If possible, conduct tests with both motor types to understand their performance and functionality.

For example, the rotor speed is often used to measure motor speed. So if you plan on using a high rotational speed for your application, consider looking at induction motors with stator voltages higher than synchronous motors.

Another factor to consider is the power rating. Higher power ratings mean faster speed but also more power consumption. To keep energy consumption low for your application, consider induction motors with lower power ratings than synchronous motors with higher powers.

In terms of size and output, induction motors are smaller and can produce more voltage output than synchronous motors. However, synchronous motors are generally easier to start and operate. 

Overall, conducting detailed research is vital before making a final choice.

What are the advantages of Synchronous motors?

First, synchronous motors have high efficiency, meaning they use less energy than traditional motors.

Second, they provide precise speed control, as the speed is based on the frequency of the power supply.

Third, they are smaller than other motor types, making them suitable for compact spaces where size is an issue.

Fourth, their speed is consistent regardless of load changes or voltage fluctuations due to how they are designed.

Lastly, synchronous motors are extremely reliable and require little or no maintenance over long periods.

synchronous motor

What are the benefits of Induction motors?

Here are the benefits of induction motors:

  • Relatively low cost
  • High starting torque over a wide speed range
  • Very rugged construction and simple maintenance requirements
  • High efficiency compared to other types of motors
  • Ability to be designed as both single-phase and poly-phase motors
  • Can operate with variable frequency drives for more precise speed regulation

Conclusion

We hope you have found this comparison helpful and helped you make a better-informed decision. If you are looking for motor cores that efficiently provide power, we have just the thing for you – our range of motor cores. Want to know more? Contact us today!

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