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Differences Between Synchronous & Induction Motor

Comparison Between Synchronous & Induction Motor

AC machines are classified into Synchronous & induction machine also known as the asynchronous machine. They are the most used machines in the industry with many applications. Before going into the comparison between these two types, let’s look into it one by one.

Differences Between Synchronous & Induction Motor

Synchronous Motor:

It is an alternating current machine which runs at a fixed/constant speed known as the synchronous speed. The synchronous speed depends on the frequency of the applied voltage. Its speed does not vary with the increasing of the load.

It can be used as an alternator (generator) when driven mechanically. It can generate between 150 KW & 1MW with a speed of 150 to 1800 r.p.m.

It is not a self-starting motor & needs some other means to provide the necessary (near synchronous) speed. it can operate at both lagging and leading power factor. The most important part is that it either runs at synchronous speed or it does not.

Induction Motor:

The asynchronous motor or induction motor is a rotating transformer with the primary winding as stator (stationary part) and the secondary winding as the rotor (rotating part). The rotor is powered using the electromagnetic induction from the stator winding.

There is no electrical connection to the rotor. There are no brushes used which also decreases the electrical loss. It is a self-starting motor which starts from rest. By increasing the load the speed of induction motor decreases.

Differences Between Synchronous & Induction (Asynchronous) Motor

Synchronous Motor Induction Motor
It runs at a constant speed known as synchronous speed for a given frequency even after increasing the load Although its speed depends on more than just the line frequency, It decreases with increasing the load
It has no speed control ability Its speed can be controlled using a separate circuit.
It is not a self-starting motor; it needs external means to provide the necessary (synchronous) speed. It is a self-starting motor, it starts from rest up to its full speed without any other source.
It can operate on both lagging and leading power factor, which varies by changing excitation It only works on lagging power factor and it cannot be controlled.
It requires a separate DC excitation for the rotor windings It does not need any DC excitation as the rotor is powered through induction.
The torque does not vary with change in the line voltage The torque varies with the line voltage.
Best contender for low-speed application They are excellent for high-speed applications
More costly and complicated with high efficiency and require frequent maintenances Cheaper as compared to a synchronous motor with low efficiency and require minimum maintenance.

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