Variable speed drive motors

[kmuhsen]

If a big motor is controlled by vraiable speed driver, does it need a soft start control like star-delta. please advise

 

[bfuchs]

No it doesn't.<br>
The variable speed drive (aka variable frequency drive) controls the frequency of the signal arriving at your motor. This in turn controls the speed of roataion of the motor, and makes sure you have a smooth start-up.<br>
It will control the motor from 0 rpm all the way up to the maximum rotation speed.<br>
<br>
If you mainly run at maximum speed, it could be a good idea to use a bypass contactor to get the VSD off the network, though...<br>
<br>

 

[umn]

Just to add some more info:<br>
<br>
The speed has a direct relation to the frequency- higher the frequency, higher the speed of rotation. Hence, the variable speed drives start by issuing power from very low frequencies, and then steadily increase the frequency to increase the speed.<br>
<br>
Most VSD's also control the voltage applied. When the motor starts with low frequency, the winding offers much less reactance and the current can shoot up with normal voltage (magnitude). Hence, while starting with low frequency, the peak-to-peak voltage also is made low. <br>