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# Is it possible to operate motor by VSD if motor rated voltage is greater than ATV supply voltage?

Published date: 07 May 2019

THere is one fact, than ATV output voltage can be regulated from zero to the max value that corresponds to ATV input voltage. So if you use 400V supply the max voltage at the ATV output can be 400V.
Diferent rated frequency in input (supply) and ouptut (motor) voltage does not play role at all. Input AC circuit and ouptut AC circuit are separated by DC bus, so no matter the difference in frequency.
Speaking about the ATV output voltage, the limited output voltage does not necessarly mean a problem. Everything depends on speed operating range and the load.
As you know, the torque in the motor is build when the motor is magnetized (flux exists). The reated torque in the motor can be achieved when motor has rated flux which means that as fas as we can respect u/f = constant, the motor will have rated flux.
For example if motor rated voltage is 440V, 60Hz, the rated constant u/f = 440V / 60 Hz can be kept up to the limit of supply voltage 400V and that is 440/60=400/f_limit
Hence f_limit gives you 54.5 Hz
As a result, if the drive is suplied by 400V, 50Hz and so max voltage at the output is 400V then
your 460V/60Hz motor will get rated torque up to 54.5Hz. If you go over this speed, the motor wil work in filed-weakening area (motor will gradually loose the torque). If you do not need 100% of the torque (depends on application) then you can even operated the motor in field weakening area.

Summary

Using 400V supply, surely no problem to operate 440V/60HZ motor up to 54.5Hz. Rated torque in the motor can be built continuosly, without drive or motor overload.
Over 54.5Hz, everythings on the torque required by load. The torque in the motor will be lowered, (at 60Hz it will be aprox 80% of rated torque). It can be enough for loads that do not require more that 80% of the motor rated torque. If the load requires more torque, then the only solution is to increase the supply voltage at ATV input.