I would be insisting the machine-tool manufacturer reasonably demonstrate to you and your client that power quality is unambiguously the cause. There was lot of fingerpointing up to about 15 years ago with major machine-tool producers, and most fixed their designs to work properly on the average industrial power system. Get the machine vendor to find the exact problem, at their expense if they are so sure of themselves, unless prior to purchase they provided a clear disclaimer that any problems were not theirs to deal with,
There are special-purpose, high-harmonic drive-isolation transformers rated 230∆—230Y/133,
that would allow establishing a separately-derived system with local system grounding for each machine, but are pricey with no guarantee as to effectiveness. Smaller sizes have ±5% taps for minor voltage adjustment—~219V on primary. would give ~230V on the secondary.
www.acmepowerdist.com/pdf/Page%2046.pdf and
www.acmepowerdist.com/pdf/Page%2048.pdf Hold their feet to the fire
!
