Difference Between Synchronous and Induction AC Motors

Difference Between Synchronous and Induction AC Motors

 AC motors are widely used across both domestic and industrial applications. They convert alternating current (AC) into mechanical motion — but not all AC motors are the same. The two primary types are Synchronous Motors and Induction (Asynchronous) Motors.

In this guide by Regent Electronics, we’ll explore the key differences between Synchronous and Induction AC motors based on various parameters like excitation methods, speed, starting mechanism, efficiency, usage, and more.


🔧 What Is an AC Motor?

An AC motor converts alternating current electrical energy into mechanical energy using the principle of electromagnetic induction. Based on their construction and operational characteristics, AC motors are mainly categorized into:

  • Synchronous AC Motors
  • Induction (Asynchronous) AC Motors

Let’s break down each motor type and compare their functionalities.


⚙️ 1. Synchronous AC Motor

A Synchronous Motor is one that runs at a constant synchronous speed, regardless of the mechanical load. This speed is determined by the frequency of the AC power supply and the number of poles in the stator, calculated as:

Synchronous Speed (Ns) = 120f / P
(f = frequency in Hz, P = number of poles)

🛠️ Construction:

  • Stator: Contains axial slots with windings designed for a specific number of poles.
  • Rotor: Usually, a Salient Pole Rotor with DC field windings powered by slip rings. Alternatively, permanent magnets may be used.

⚡ Working:

When powered, the stator produces a rotating magnetic field. However, due to rotor inertia, the rotor does not start on its own. This is why a synchronous motor is not self-starting. It requires an external mechanism (like a pony motor or damper windings) to bring it up to synchronous speed.


⚙️ 2. Induction (Asynchronous) AC Motor

The Induction Motor—also known as the Asynchronous Motor—operates by inducing current in the rotor from the rotating magnetic field of the stator. It always runs at a speed slightly lower than synchronous speed, hence the term asynchronous.

🛠️ Construction:

  • Stator: Wound for a specific number of poles.
  • Rotor: Can be a squirrel cage rotor or a wound rotor. In squirrel cage motors, rotor bars are permanently short-circuited using end rings.

⚡ Working:

When the stator is energized by AC supply, it creates a rotating magnetic field that induces current in the rotor conductors. This induced current interacts with the magnetic field and generates torque, causing the rotor to rotate.

Unlike synchronous motors, induction motors are self-starting and widely used due to their simplicity and cost-effectiveness.


🔍 Side-by-Side Comparison: Synchronous vs. Induction AC Motors

ParameterSynchronous AC MotorInduction AC Motor
Power SupplyStator: AC supply
Rotor: DC supply via slip rings
Stator: AC supply only
Type of ExcitationDoubly excited (AC for stator, DC for rotor)Singly excited (AC only)
Operating SpeedConstant and equal to synchronous speedAlways less than synchronous speed
Starting MechanismNot self-starting; requires auxiliary meansSelf-starting
Power Factor ControlCan operate at leading or lagging power factor by adjusting excitationOperates only at lagging power factor
Primary UsagePower factor correction + driving mechanical loadsDriving mechanical loads
EfficiencyHigher efficiency for the same voltage and power ratingSlightly lower efficiency compared to synchronous motor
ConstructionMore complex due to rotor excitation and slip ringsSimpler, especially in squirrel cage type
CostMore expensive due to complexity and materialsMore economical and widely available

💡 Applications of Synchronous and Induction Motors

✅ Synchronous Motor Applications:

  • Power factor correction
  • Precision timing devices (e.g., clocks)
  • Robotics
  • High-performance industrial systems

✅ Induction Motor Applications:

  • Household appliances (fans, washing machines)
  • Industrial machinery (pumps, conveyors, blowers)
  • Air conditioning systems
  • Elevators and cranes

📌 Conclusion

Both synchronous and induction motors are essential components in modern electrical systems. Choosing the right motor depends on your specific application needs:

  • Need precise speed and power factor correction? Go with a synchronous motor.
  • Looking for a reliable, self-starting, cost-effective motor? The induction motor is your best bet.

If you’re still unsure which motor suits your application, feel free to contact our experts at Regent Electronics. We’re here to help you make the right choice for your automation and electronics needs.

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