Reverse fed transformers

[Jraef]

...
Another concern is insulation rating of secondary conductors, 600v.
If secondary is ungrounded a phase fault will increase voltage on other phases to 830 v exceeding insulation rating. Also seems that it would impact secondary voltages on down stream single phase transformers if one of their primary legs went to 830 v.

No, not sure where you got that. If you have an ungrounded delta system, when the first ground fault happens you just go to having a corner grounded delta system. That's why a lot of industries used ungrounded delta systems in the past.

As to the interrupting capacity, why are you concerned? If you are stepping up from 480 to 600V delta, then at the other end, going from 600V down to individual 240/120V single phase transformers, the only place the IC is going to matter is at the primary OCPD of those transformers. Given that its origin is that 480-600V step-up transformer, I seriously doubt that you can have more SCA at those fuses than what any basic fuse is rated for. If you have a 600V panelboard that is distributing out the 600V to those transformers through breakers, yes, that's maybe a concern. But I have never seen a 600V rated breaker that has less than 14kAIC, so your transformer would need to be about 500kVA with a 5%Z to make that a problem.

As other pointed out, your only immediate problem I see is that the 600VD must either be corner grounded or have GFP to be legal.

 

[jim dungar]

If you have an ungrounded delta system, when the first ground fault happens you just go to having a corner grounded delta system.

It is possible that during an arcing fault condition the voltage to ground can approach 2x the nominal L-G voltage. However we do not normally consider this to be an issue with today's insulation systems (I have never seen a warning about it). I did not check these numbers and I don't have that good of a memory. I seem to recall it has to do with resonance.