Synchronous motors
are constant speed motors. They run at the synchronous speed of the
supply. They are generally used for constant speed operation under no
load conditions such as to improve the power factor. Synchronous motors have fewer losses than induction motors at a given rating.
The speed of a synchronous motor is given by
N = 120 f / p
Where, f = supply frequency and p = number of poles
As you can see, the synchronous speed depends on the frequency of the supply and the number of poles of the rotor. Changing the number of poles is not easy, so we do not use that method. However, with the invention of solid-state devices, the frequency of the current fed to the synchronous motor can be varied. We can control the speed of the synchronous motor by changing the frequency of the supply to the motor.
N = 120 f / p
Where, f = supply frequency and p = number of poles
As you can see, the synchronous speed depends on the frequency of the supply and the number of poles of the rotor. Changing the number of poles is not easy, so we do not use that method. However, with the invention of solid-state devices, the frequency of the current fed to the synchronous motor can be varied. We can control the speed of the synchronous motor by changing the frequency of the supply to the motor.
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