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VSD Motor Power, Speed & Torque – How and Why
We came across a situation recently on site where an induction motor being driven by a VSD at a reduced speed had the operators asking "Why is the motor running at the rated current but not at the rated power?"
It was actually a very good question and one that we thought we would share with you all.
First of all there are a few things to remember about a motor;
It was actually a very good question and one that we thought we would share with you all.
First of all there are a few things to remember about a motor;
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The most basic method of control for an induction motor on a VSD is the Volts per Hertz (V/Hz) method, also known as open-loop or scalar control. This is where the VSD controls the motor speed by maintaining a constant ratio between motor voltage and frequency, as the frequency of the motor is reduced so is the voltage by the same ratio to maintain a constant magnetic flux.
If we have a look at the motor power formula, we see that the speed of a motor (shown as rpm) directly effects the power of a motor;
If we have a look at the motor power formula, we see that the speed of a motor (shown as rpm) directly effects the power of a motor;