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Effect of the change of the supply frequency.


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Dear All,


What is the effect of the change of the power supply frequency on a motor ? A motor will run faster with higher frequency, but will it draw less current and will its power reduced ?. Assume that the voltage will remain the same on both frequencies.



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Hello rizwan


Welcome to the forum.

If you change the frequency of the supply to a motor, you will change it's speed. As you change the frequency, you will also change the flux unless you alter the voltage also.


Induction motors are designed to operate close to the maximum flux. If you increase the flux, you reach saturation. This results in a rapid increase in magnetising current and a dramatic increase in iron loss.

If you reduce the flux, you reduce the maximum torque that the motor can develop.

It is important to try to keep the V/Hz ratio constant. If you do not, you could cause the motor to overheat and fail, or you could cause the effective power / torque rating of the motor to reduce.


Remeber, when you increase the speed of the motor, the load will spin faster and in some applications, a small increase in speed can result in a large increase in load and overload the motor.


Best regards,

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