Comparison between Synchronous Motor and 3-Phase Induction Motor

Comparison Between Synchronous Motor and 3-Phase Induction Motor

In this short post let us see difference between the 3-Phase Induction Motor and the synchronous motor.
Before proceeding further let us refresh the basics of both the motors.

Motors operation in the AC (alternating current) are classified as follows:
(1)  Single Phase Induction Motor
(2)  Three Phase Induction Motor
(3)  Synchronous Motor

Three Phase Induction Motors:

The three-phase induction motor is further classified into two types namely squirrel cage motor and slip ring induction motor.

Of all the ac motors, the 3-phase induction motor is widely used for various kind of applications.
They have the following advantages and disadvantages.


  • The construction is simple, rough, unbreakable.
  • It is low-cost, reliable.
  • It is self-starting, no starters required.


  • Its speed decreases with increase in load.
  • Its speed can not be varied without losing some efficiency.

Synchronous Motor:

  • A synchronous motor is identical in construction with an alternator or AC generator.
  • Similar to DC machines, a synchronous machine may be used as an alternator when driven mechanically or as a motor when driven electrically.

The following table gives us the Comparison between synchronous motor and 3-Phase Induction Motor

3-Phase Induction Motor Synchronous Motor
It is self starting. It is not self starting.
The actual speed of the induction motor falls slightly with increase in load. Synchronous motors run at constant speed at any load for a given frequency.
Induction motors can be run with lagging power factor only. The power factor is low at light loads. Motor can be worked under various power factors, such as lagging, leading and unity.
No exciter is required. The motor requires a separate DC exciter for its field supply.
Changes in voltage applied in induction motors affect the torque. The torque is proportional to the square of the applied voltage. Changes in voltages applied in synchronous motor do not affect the motor torque. The break down torque of the motor is approximately, proportional to the applied voltage.
The cost of induction motor is low. The cost of synchronous motor is high.

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