Backfeeding Grounded Delta Services

[Shoe]

I don't run into these services often. However, I'd like to consolidate some individual grounded delta services in a facility onto one service.

My thought was to provide a new 480V/277V wye service and use step-down / isolation transformers to feed the existing 240V and 480V corner-grounded delta services.

Is there any issues with going from a wye-connected and grounded service through a transformer to a corner-grounded delta? I want to make sure the existing equipment and panelboards on the corner-grounded systems (most of which are 2-pole) are not compromised.

Thanks.

 

[jim dungar]

Is there any issues with going from a wye-connected and grounded service through a transformer to a corner-grounded delta?

It is done all of the time, when using isolation transformers.

 

[GoldDigger]

It is done all of the time, when using isolation transformers.

There are some potential issues when there are unbalanced loads on the wye secondary side of a wye-wye transformer, or unbalanced source voltages. But source wye to load delta should be fine.
Jim, should the service neutral be connected to the primary side wye center point in this case?

 

[jim dungar]

Jim, should the service neutral be connected to the primary side wye center point in this case?

Ignore the fact that the service has a L-G connection.

The transformer should be ordered with a 480V delta primary.
We don't buy motors with 'neutral' connection, we don't need to have them on transformer primaries either.

As a general rule, non-utility installations will almost never use transformers with wye connected primaries at <600V.

 

[Shoe]

Thanks for confirming, Jim. Attached is a scaled-down version of essentially what I plan to do, for the benefit of clarification.

 

[jim dungar]

Thanks for confirming, Jim. Attached is a scaled-down version of essentially what I plan to do, for the benefit of clarification.

It looks reasonable.
Make sure your protective devices are rated for Grounded-B phase systems.