hummel6817,
As you can see from the responses, there is really nothing we can do for you beside guessing at things. You really need a licensed electrician qualified in industrial distribution systems to take a look at this for you.
One issue raised is the possibility that although you may have a transformer that is LABELED as Delta-Wye, it may not be used in that way. In an old-school thought process, it was somewhat common in industrial plants to use a 480V ungrounded Delta distribution system. The thinking was that in that type of system the plant will continue operating with the first ground fault, because you simply go from an ungrounded Delta system to, effectively, a "corner grounded Delta" system and the plant keeps running as if nothing hapoened, other than at that initial fault point. So no fuses blow, no breakers trip, the production doesn't stop. It was kind of like a "Damn the torpedoes, full speed ahead!" approach to power distribution.
The thing is, this kind of system was popular when industrial power electronics, such as VFDs, Servo drives etc. were very uncommon. These types of devices are, for the most part, designed to be used on solidly grounded Wye distribution systems where the voltage reference from line to ground is 58% of what it is line to line. In an ungrounded Delta, or "fliating" ground system, the line to ground voltage reference is potentially the same as the line to line potential under the right circumstances. Not only are the line side components of things like drives often selected for the lower (58%) voltage reference, they will also have line protection components (MOVs for example) on them that are themselves referenced to ground as well. So if connected to an ungrounded Delta system, those line protective devices become the Wye grounding point of your entire facility, for a few milliseconds until they vaporize. Then they are no longer there to protect the rest of the device. As was said, you may go on for years never knowing that there is an issue, but then one day there is, and the damage is catastrophic (from the device standpoint). So bottom line, modern industrial plants no longer use ungrounded Delta distribution systems unless a lot of special care is taken on how anything with electronic power supplies is connected (usually by using smaller Delta-Wye isolation transformers to create a local grounded Wye system just for those devices).
But again, this is pure speculation, because we are not there to look at what you have and take measurements. Hence the necessity of getting a local qualified professional involved.
