AC Motors are mainly of two types, one is synchronous motor and other is an asynchronous motor. Asynchronous motor is also known as an induction motor. Both Motors are widely used electric motors. Although there is a big list of differences between these two motor here we will learn some basic and major differences as given below:

Synchronous Motor

  1. Synchronous motor run at a constant speed i.e. at synchronous speed
  2. Synchronous motor required DC excitation to its rotor.
  3. It is not self-starting.
  4. Power factor can be changed from lagging to leading and vice versa.
  5. The speed of a synchronous motor is constant at all load.
  6. Synchronous motor rotate because of magnetic locking between rotor poles and stator poles.
  7. Synchronous motor cost is high and required regular maintenance.

Induction Motor

  1. Induction motor always run less than synchronous speed.
  2. Induction motor does not require any extra DC excitation source.
  3. It is self-starting.
  4. Induction motor always operates at lagging power factor.
  5. When the load on induction motor increases its speed decreases.
  6. Three phase induction motor operates on induction principle.
  7. It is less costly and requires less maintenance.

Difference Between Synchronous & Induction Motor


Synchronous motor

Induction motor

1 Construction is complicated Construction is simpler, particularly in case of cage rotor
2 Not self-starting Self-starting
3 Separate DC source is required for rotor excitation Rotor gets excited by the induced e.m.f so separate source is not necessary
4 The speed is always synchronous irrespective of the load The speed is always less than synchronous but never synchronous
5 Speed control is not possible Speed control is possible though difficult
6 As load increases, load angle increases, keeping speed constant at synchronous As load increases, the speed keeps on decreasing
7 By changing excitation, the motor power factor can be changed from lagging and leading It always operates at lagging power factor and power factor control is not possible
8 It can be used as synchronous condenser for power factor improvement It cannot be used as synchronous condenser
9 Motor is sensitive to sudden load changes and hunting results Phenomenon of hunting is absent
10 Motor is costly and requires frequent maintenance Motor is cheap, especially cage rotors and maintenance free
Difference Between Synchronous & Induction Motor

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