Delta-Delta transformer feeding shop 480v loads

[ECE2001]

A number of years ago and long before my time, an addition was added to the building were I work. We have 240 3-phase coming into the building and is stepped up to 480 with a Delta/Delta xfmr. We use the 480 in the shop to feed servo drives and related machinery which we manufacture and supply to major appliance and automotive OEMs. The manufacturer's instructions for some of the servo drives suggest an isolation transformer with a grounded neutral point. My guess is that they are referring to a Delta-Wye xfmr. As long as I've worked there, the 480 in the shop has been prone to fluctuations and I'm wondering if the Delta/Delta step-up xfmr could be suspect. Other loads on the xfmr include CNC mills (VFD), a water-jet machine (VFD), perhaps some HID lighting, and some induction motors for ventilation (I'm just guessing about some of this because I never saw any diagrams).

 

[Psychojohn]

It may be an overloaded transformer or a large amount of harmonics from all the drives.
You would need to find out where the voltage fluctuations start. Primary or Secondary of the transformer.
Are these 3 phase servo drives?
Servo drives produce alot of noise, and the line filtering works best when it has a common neutral point to referance to.