I have a couple of concerns, more so than code answers. I think that all the code concerns were addressed already.
I’ve had this question a few times in technical support (I went from steel mills to flying a desk....I still haven’t got used to it.)
I would verify that the motors do not have 2 sets of connections in the pecker head. A lot of 575 v motors are in reality 460/575. If it does, just change the connections to your existing bus voltage.
If you are across the line starting these (I just conferred with one of my peers about this) your motors have to be way over-sized to be running like you say. The de-rating factor is 36% because of the change in current. Remember that current is not linear to torque when voltage and frequency are fixed. It concerns me also about the temperature rise times involved with this and the insulation ratings in general.
The drive way of looking at this (which is what I do all day) is as follows. The volts/Hz ratio is 9.58 based on a 575/60 relationship. With that said, take 460/575 which yields .80. 80% of 60Hz is 48Hz. This is the real key; the motor has no idea or cares what is going on until 48Hz with a VFD. After 48Hz the torque starts tapering off just like it would if you had a basic 460/60 trying to run the motor beyond 60Hz. If torque is a concern at higher speeds, realize that it's not going to perform.
Carl
PS. I really enjoy reading this forum...thanks all.
