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Bilge Rat
motors and controls.........
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8,605 Posts
If there are VFDs involved, I would highly recommend installing a 480∆ - 277/480Y transformer.

The primary side doesn't care about voltage to ground, in your case it'll be 3Ø 3 wire. One of the phases is already grounded, if you can find where the phase and ground are bonded together, you'll need to pull a ground wire from there with the 3 phases. The fact that it's a corner grounded ∆ doesn't matter.

The secondary side is a separately derived system. There's no electrical connection between the 2 sides so you'll need to bond the 277 neutral to ground.

When you're done, the incoming primary ground, the secondary ground, the secondary neutral, the transformer frame, and if applicable, the building steel and the ground rod (or whatever the grounding electrode is), should all be connected together.

If you bond the 277 neutral to ground at the transformer, don't bond it to ground anywhere else.
 

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Bilge Rat
motors and controls.........
Joined
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8,605 Posts
Its also a easy fix. They simply go to the nearest bank of voltage regulators. Plug in a volt meter then turn the dial down.
We owned our own sub-station so we would make the adjustments our-self on the 25kv lines when we started to have problems with high voltage and vfd's.
Some of the more modern models have load tap changers that can be operated under load. A lot of these have voltage monitoring and will automatically adjust the taps to whatever voltage is selected.

The one that supplies the OP isn almost certainly the manual type and it's simply tapped too high.
 
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