# Vfd

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Hi

Right now we have one machine which runs with VFD. The current specification of motors are 1740 rpm at 59.2 Hz ant 380 volts. The KW is 5.5.This is maximum as given.

I would like to increase the speed of motor by increasing the frequency. I would like to know the potential problems in doing so. My intention to increase frequency by 10% of maximum.

regards

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The torque design rating of a motor is based upon it's design voltage and frequency, denoted by a "V/Hz Ratio". So if you have a motor designed for, in example, 380V 50Hz, it is designed to provide a certain amount of torque at a V/Hz ratio of (380/50) 7.6V/Hz. So as long as you maintain that ratio, all is right with the motor.

If it is a pump or a fan however, load generally increases at the cube of the speed. So if your motor was sized to do a job at 50Hz, and you are running it at 65Hz, the load on the motor will increase by (65/50 = 1.3, cubed = 2.86) 286%! So now your load has almost tripled AND your motor torque has dropped by 23%, so it is highly unlikely to work unless that motor was 3 times as big as it needed to be to start with.

"He's not dead, he's just pinin' for the fjords!"

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