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How to speed control of 3-phase induction motor


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Posted 28 May 2005 - 03:43 PM

How to speed control of 3-phase induction motor

#2 marke

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Posted 28 May 2005 - 09:11 PM

To control the speed of a three phase induction motor, you must vary the frequency and voltage of thw upply applied to it. If you halve the frequency, the motor will run at half speed. If you reduce the frequency, you must also reduce the voltage such that the ratio of v/f is kept constant.
There are inverters available from most electrical manufacturers that are designed for the speed control of induction motors.
Have a look at http://www.motor-control.co.nz for some examples.

There are some special motors with a very high resistance rotor that can be reduced in speed by a reduction in the applied voltage. Thes are a high slip motor with a high resistance rorot and sometimes are used as the integral moto on a fan unit. Do not try tovary the speed of a standard induction motor by voltage control as the motor will be damaged.

Best regards,




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