Calculating Balanced Voltage

Probably yes, IF you have more information. You do not mention whether or not the voltage (unloaded) is balanced or not, nor do you have any phase information for the currents -i.e. load power and power factor on each phase. Also, is the output Y, Y grounded at neutral, or delta. Ifg grounded, what is the neutral current?

Don, this is the information I collected:

Volts L1&L3 L2&L3 L1&L2 Unloaded 225.4 222.4 238.5 Loaded 205.2 194 226.7

Volts L1&G L2&G L3&G Unloaded 121 119.3 189.5 Loaded 110 108.6 156

Amps L1 L2 L3 Unloaded 19.1 19.1

This morning I put 60 uF between L1 and L3. It brought down my unloaded idler Amps from 19 to 14 amps on L1 and L2. It however made no difference when I was running my 10hp compressor. I have problems starting my compressor under load and thought balancing the amps would help. My compressor does unload correctly so it has to be an electrical problem. If I put the run capacitors across the compressor motor will that help ? - But the I dont see how that would be isolated from the idler circuit.

Off hand this looks as if you have a high impedance on line 3. This is likely the reason that the voltage on 3 is high. Have you accounted for all loads? The balance is poor. Without ground, there is no reason for the voltages to ground to be equal but they shouldn't be this far out. Again, is it Y or delta ? If Y, where is the neutral connected? Are the load motors Y or delta and, if Y , are the neutrals tied to the motor frames and hence to ground?

Your line to line voltages aren't balanced but are not bad enough to cause the current variation shown. Your loaded line to line voltages follow along. The unloaded currents seem to indicate the presence of a damn near single phase load between line 1 and 2 and the loaded currents are similar. You do have a large neutral shift. in both cases. Line 3 appears to have a high impedance either in the converter or in the motor. What load is actually present in the unloaded case? You indicate idler 15Hp and load 10HP which makes little sense without more detail . Have you any measurements of the motor impedance (motor disconnected from supply) between phases and phase to frame as well as frame to ground?

In any case it looks as if you are almost single phasing which does present problems.