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Differences Between Synchronous and Induction Motor

Differences Between Synchronous and Induction Motor

We have two major types of AC motors.They are synchronous and induction motor,synchronous motor runs at synchronous speed where induction motor runs at less than synchronous speed.In this article we are going to discuss on comparisons between synchronous and induction motor. There are so many differences between synchronous motor and induction motor like excitation,speed control.etc.Most important points are listed below.

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

Read Here: Differences B/W Induction Motor & Transformer
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