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In my experience this is one of the things they don't try to wiggle out of, even if it's just one small customer. It's too easy for the customer to test and show that they're outside of their public utility requirements. If they don't respond and you call the utility commission, they will still have to fix it, and deal with all the utility commission red tape as well.

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.
 

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Bilge Rat
motors and controls.........
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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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You state that the voltage coming from the Utility is too high. I have a challenge, if the plant has down times where you can kill all the equipment, disconnect power to all the equipment and measure the incoming voltage phase to phase. I suspect your going to find that the incoming voltage will be around 500 VAC. You stated that the plant has a lot of equipment that uses VFD units. These have THREE contributing issues, first the input section of the VFD creates bad harmonics which will effect voltage measurements. Second, the input capacitors will act as power factor correction when lightly loaded, raising the incoming voltage. Third, electricians in the past have added the VFD's to existing equipment running the VFD outgoing power through the same conduit as normal 480VAC circuits. In this configuration even a small VFD will through so much harmonic energy on the incoming power that a inexpensive NON-VFD type DVM will read this as high voltage. We have to use the Fluke 87/89 meters to measure voltage with high harmonic power levels to get accurate power. Or you can use an old analog Simpson voltmeter which won't read the peak harmonic voltage levels. I've seen the 525+ phase to phase voltage a lot over the last 40 years working with VFD units. The correct fix if it's harmonics on the power line is either input line reactors on each drive (not the most efficient method) or harmonic filters (much more expensive).
 
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