Single phase and three phase for a motor

[Mr. Pickle]

Working on a lift station project where the Client has a 3-phase generator. The utility will only provide single phase power. Since the load are motors, I am thinking of using a VFD for phase conversion for the motors (motors will be 3-phase). Do you see any issue with using a single phase service but a three phase generator? So when the transfer switch is switched over the VFD input will be single or three phase pending on the selected source. If the VFD and feeder breaker are sized for a single phase load, do you see any issues of doing this?

 

[Besoeker3]

What are the voltages for single phase and for three phase ?

 

[Jraef]

Assuming you are talking about 240V on either source, it should be doable. The VFD will need to be de-rated per the manufacturer’s instructions for a single phase input, which means it will be over sized for the 3 phase input, but that’s not really a problem. Just to be clear though, you can’t use one VFD as a phase converter and run multiple motors separately, you will need a VFD for each motor.

Be aware of any restrictions from the VFD mfr regarding using a delta power source, which 240V 3 phase always is. You may need to remove some protective elements inside of the VFD, which may affect the warranty. If you have a 240/120 3 phase 4wire delta generator, where one phase is split to provide 120/240 single phase, you may want to consider just using that set of windings as the single phase backup power to the pump station, then everything stays the same. Or if the pumps are available as single phase, you don’t need the VFD at all.