UPS needs Grounded WYE source -Only Delta Available 2

[ExportKW]

Hi,
Our Customer purchased a new UPS that requires the input source to be a 480VAC grounded WYE. After the new UPS was installed it was determined that the Utility source is a 480 Delta.

The UPS is rated 300kVA but never loaded beyond 50%. So one choice is to install a 300 kVA 480DY isolation transformer. This seems excessive? Could a zig-zag transformer be used upstream of the UPS input to derive a neutral?

The customer has some load that could be connected upstream using a 480Y:240D transformer. Would the Wye primary derive a neutral?

My understanding is that the UPS requires the grounded wye due to components on board that are rated and connected for line to ground voltage as well as during a discharge for safety reasons since the input contactor is opened on discharge.

Any tips, advice or experiences would be helpful.

Thanks!

 

[RalphChristie]

Are you the utility?

If yes, then either a zig-zag transformer or a star-delta (480V star) transformer can be used to create a neutral. Zig-zag transformers are not always easily obtainable, most probably it will be a special order, and thus expensive. However, a zig-zag transformer will be smaller than a star-delta transformer for the same fault current capability. Remember if you'll do it your system will change from a ungrounded system to a resistance/reactance grounded (depending on how you ground the neutral)system. This will mean you'll have to make some changes in your system. (protective schemes, lightning arresters, etc)

If not, you'll have to consult with the utility first because you will be changing the grounding scheme and they'll have to do some system changes as explained above.

An isolation transformer will be the easiest option without major changes.

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[dpc]

I agree with Ralph Christie. The zig-zag transformer would probably work, but I don't think you would save any money over a much more easily obtained delta-wye isolation transformer.