I've selected 230/400V motors (delta/star) and corresponding 400V VFDs for pump motors. Now I've been asked why I haven't selected 400/690V motors (delta/star), that are the standard and usually connected in delta. The manufacturer says there that the both motors types will consume (approx.) 8A at 400V and there is no special requirement for the torque.
Is anyone seing an advantage to have the 400/690V motors instead of the other ones?
These motors 400/690 are used for star/delta switch. When connected to star, they got 230V at each phase, when switched to delta they got nominal 400V voltage. They can also work nominally at 690V if star connected. This is a standard for such motors, mostly they use a star/delta swith or sequence by using three contractors and pneumatic delay device.
In your case, using a VFD, this motor should be connected in delta wiring. It won't make any difference for your application.
There is no advantage using such motor, this is just standard. You can get also 230/400V motor, but probably they will charge you extra money for swapping.
There is no particular reason to elect one over the other if other important factors are the same. Rated current is one factor to consider. Comparing efficiency, price and availability are other important factors. The first consideration should have been a statement by the manufacturer regarding suitability for use with a VFD. For a VFD, the most important factor is winding insulation ability to withstand the voltage stress due the switched voltage waveform. Another consideration for VFDs is the continuous torque rating at reduced speed, but that is not a factor with centrifugal pump loads. You might also consider the need for protection against bearing currents. Voltage stress and bearing current protection options may be offered by the VFD supplier, but it is still a good idea to check the motor manufacturer's recommendations.
