Hi all,
I have a neura heat pump.The refrigeration compressor is 5kw 400 volt 3 phase.
The mains supply to the neura control panel is 230 volt single phase.
400 volt 3 phase is achieved from the single phase supply via an adapted allen Bradley inverter and a bank of capacitors.
The inverter is now dead.
According to neura this system was not a success and the replacement for the motor driver is 1500 euro.
What options have I?
I was thinking a 6kva step up transformer 230volt 1p in 400v 1p out supplying a 400v 1p 5kw inverter
Any opinions?
The underlined portion of this has me concerned. A VFD can convert single phase to 3 phase, but does not inherently increase the voltage. That is typically done with a transformer. You can ALSO do it with what is called a "voltage doubler" circuit; which is a set of capacitors and diodes arranged to step up DC voltages. You would accomplish that then by rectifying the single phase AC to DC, then run that DC through the doubler and into the DC bus terminals of the drive, bypassing the drive's own rectifier. Many drive mfrs do this for using 115V single phase input to a VFD to run a 230V 3 phase motor, but only up to 1HP (.8kW) because the challenges multiply exponentially with size. A company in the UK did this for a while on larger drives and higher voltages, but without the sanction of any drive mfrs, wheo ended up bearing the brunt of angry users when they failed. So they have been forced to stop from what I've heard. This sounds like it was maybe one of those, or a copy of it. Whatever was done, it was not done with AB's blessing.
Your alternative solution is a viable way to do this. However, DickDV has missed an important fact in his suggestion. You are going to be doing the single to 3 phase conversion at 400V, not at 230V. He is correct that some 230V drives do not need de-rating at the smaller power ranges, only because at some point, the component costs are so low that it doesn't make sense to use different power components any more, so they are already over sized to start with. But that ONLY holds true for 230V designs. At 400V, nobody does this.
Bottom line, yes, you can use the transformer to step up the single phase to 400V first, then go through a VFD, but you will have to use at least a 10kW rated VFD to get there successfully, maybe larger depending on the ambient temperature of the drive, because drives that convert at a 50% de-rate also lower the maximum ambient rating to just 25C, which is difficult to attain, or they tell you to use a 65% de-rate and the standard temperature rating of the drive. The devil is in the details.
Option 2; replace the motor with a 230V 3 phase version, or better yet, check your motor to SEE if it can be reconnected as a 230V. But even then, there are very very few 230V VFDs that are rated for single phase input without de-rating by that 50%, most stop that at 3HP (2.2kW) and below. So that may not buy you anything anyway.