I am seeing an excessive amount of neutral current on a 3 phase system. It basically consists of a 3 phase 400 hz inverter to a 3 phase wye-delta transformer to a general DC power supply (rectifiers). Roughly 80% of the current is lost on the 3rd harmonic. Is there a simple solution for this problem? I've read about low pass filtering, but space is limited and I can't afford the capacitor bank space. Most information that I find is on large scale power, this has a max of only 3kW, it uses a 6kW inverter. I've also read about 12 or 24 pulse rectifiers rather than 6 pulse. The current is present without connecting anything after the transformer, so I am not sure if changing from 6 pulse to 12 or 24 will make a difference. The excessive neutral current doesn't change depending on the load, it is pretty much the same. The phasing is correct. The power factor is only about .20 to .25. I've seen this same setup with larger 3 phase generators and there is almost no neutral current.

Please help.

 

One other thing I should mention. There is about 20 feet of cable going from the inverter to the transfmormer. If I increase the amount of wire to roughly 400 feet, the neutral current and phase current drops 90%.