Thanks for clarifying those things.
The bottom line is that if you have currents varying by 20-50% between phases when running any one of several different motors and while there are no other loads at all, then there is a utility problem.? But no one from the internet, no matter their level expertise, could diagnose the exact problem from afar, and conjecture from here about root cause is not really going to help.? You need to demonstrate to the utility that they are not delivering the service. Only they can diagnose.
It's puzzling what they appear to have done so far.? It seems like you're saying they simply logged voltage for a few days when there was no load.? That's not very helpful, and certainly does not qualify as "power quality" measurement.? ?One needs data about how the system behaves under load.? ?I'm wondering if your theorizing to them about voltage and phasing actually led them to simply respond narrowly to your request -- so they proved voltage OK, as if that was the job.? But did they observe current behavior under the isolated load conditions you describe?? That's what they need to answer to.? It's hard to imagine the utility seeing that and just shrugging.
I don't think you have many options but to escalate further with utility.? I would also try to hire a local electrician with appropriate (industrial) expertise?who can do appropriate measurements, possibly help troubleshoot, and may know who/how to get the right people at the utility involved.
