I have a 3-phase Victron system made of six Quattro 15kVA inverters. During testing I noticed a significant current on the neutral both when charging from the grid and when discharging to the grid:
Discharging 30 kW → ~16 A on the neutral
Charging 60 kW → ~30 A on the neutral
System voltages are: line-to-neutral ~277 V, line-to-line ~477 V. Earth is separate from neutral and the measured voltage between earth and neutral is 0 V. The client confirmed the wiring is correct.
Could anyone tell me what might cause this neutral current? Has anyone experienced something similar with multiple Quattro inverters in parallel/3-phase? Any suggestions for checks or workarounds would be much appreciated.
Where is this neutral current measured? Grid meter? And is that direct after the supply fuses (as in; no other sources or loads between the system meter and the supply?)
Are the loads and charge currents equal over all Quattros?
Are there any single phase loads on the system?
There is too little information in the initial post to give any correct answer. A three phase system can always have neutral currents when there are single phase loads or sources somewhere in the system.
The loads are all connected on the grid side, and the Victron Quattro is used only on the input side. It charges from the grid at certain times and discharges back to the grid at other times. So there are no loads connected to the Quattro output, and effectively it is operating directly on the grid.
There is no disturbance or imbalance on the line going to the grid.
For the measurement, we used a clamp meter to measure the neutral current on the grid side, specifically on the AC input of the Quattro.
Current on neutral usually means unbalanced loads across the phases. Or a difference in power factor.
The grid in this case is the load.
Are the voltages the same across the phases? Maybe it is related to that.
Current on the neutral isn’t really a problem unless the installer didn’t size it right.
Appreciate the thought. This seems like a boots on the ground type of investigation.
Maybe put a power logger onto the systems input and check the power quality as well. It could be harmonics -if a ground neutral fault has been ruled out. This ground neutral fault includes devices that aren’t in your system as well.
So other inverters injection in your area can cause issues.
@Omar_Abu_Harb neutral current for a 3 phase system at the fundamental frequency cancels out to zero for balanced loads. Neutral current for a 3 phase system is additive for odd order harmonics. If the odd order harmonics ( switching power supplies, variable speed drives etc) is significant the neutral current can exceed the current of a single phase. In some instances when odd order harmonics are predicted to be high level, the design will call for a doubling of the neutral conductor.
I mention this because a high neutral current is sometimes an indicator of harmonic distortion which is not necessarily bad but just a fact. If the phases seem balanced and you are still seeing high neutral current it may be harmonic content which adds rather than cancels.