Delta Delta Transformer and Downstream Loads with a Neutral

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Tank11

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An existing facility has a step-down transformer that is delta-delta. If I have loads that require a neutral, is the best approach to provide a delta-wye transformer so I can derive a neutral for the unbalanced loads?

What happens upstream of the isolation transformer when the loads are slightly out of balance? Does it affect the system adversely? Curious what happens physically within the system.

Thanks!
 
Yes, add a delta-wye transformer to meet your voltage needs.
In general it is not going to affect the upstream transformer. Phases can be out of balance and run just jim dandy.
 
I would look at the stepdown transformer nameplate to see what it offers you for secondary windings. It could have a red leg delta secondary even if it's not presently used. And I would look at that transformer secondary grounding.

You are saying the secondary Voltage is wrong, so yes you need a transformer, maybe. What is the stepdown, 480 V to 240 V ? That transformer could already have a center tapped secondary winding, a red leg delta, could already have 120 / 240 available. I would look at that nameplate.

Red leg delta secondary is probably more common than a straight delta secondary.

Imbalance affects system capacity utilization. If you want to use the max available system capacity, you have to balance the load. The system will take an imbalance up to the max rating per phase.
 
Sub 54.6.jpg

Here is a picture of the nameplate rating. I don't see the red leg you're describing, is this the same as a high leg? Or wild leg?
My intention is to connect a 480-480/277 delta-wye transformer for any 277v loads and a 480-208/120 transformer for any 120v loads. Any motors or loads that are perfectly balanced can connect to distribution directly from this transformer yes?


Thanks for everyone's quick input.
 
xformer's post ( #2) likely holds the key as to the best approach. What size load are you addressing ??
 
Tank11- "red leg", "wild leg" and "high leg" (and even "orange leg") delta are the same thing. OTOH looks like that transformer doesn't have tap that anyway.

Also, since that transformer says "ASKEREL" on the plate, has it been cleaned and refilled with non PCB-containing oil? (Or is it properly labeled "Contains PCBs"?)
 
Yes, that's delta secondary only. It does not offer a center tapped winding.

It could be corner grounded or floating. Something I would want to know by looking at it. To get a Y system and the neutral you would need another transformer, yes.
 
Here is an earlier thread addressing creating a neutral with a zig-zag transformer.
I've had no experiece with this but there are folks on the Forum that can enlighten you.

Deriving a neutral: musings

In thread http://forums.mikeholt.com/showthread.php?t=87981 I hijacked a useful thread with a theory discussion. The original poster was looking to run some lighting with a 480V three wire feed, and had asked about deriving the neutral. Vern responded that you can't pull a neutral out of thin...
forums.mikeholt.com
 
If you are using a 3 phase panel after your new delta-wye transformer, you could simply balance the loads in this new breaker panel.
 
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