Transformer Neutral

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mak134

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I have a 480v/208v 3 phase delta-wye transformer that I need to feed using the 208v side as primary. However my secondary needs a neutral due to some equipment being 277v. Can I use the XO on the 208v side of the transformer to create my neutral? If not where can I get a neutral for the 277?
 
You can't. The primary and the secondary of a transformer are seperate systems. There is no electrical path between the two sets of windings. It sounds like you have a transformer with a delta 480 volt side and a wye 208 volt side. You can't get 480/277 from that transformer when using it as a step up transformer. You could install a grounding transformer on the 480 volt side, but the best way would be to get the correct transformer.
 
You will have to buy a 208 delta to a 480y/277 volt transformer. There is no way to center tap a delta configuration of windings.

If you attempt to use the XO of the primary for a secondary neutral you will be creating a potentially deadly situation.

If you only needed a wye/wye you could back feed the transformer if the manufacturer blessed it, but do to inrush problems it is not recommended.

Roger
 
Is the incoming service 480V delta or wye ?????? You might only have 3 conductors feeding the primary side of that transformer for a 110/208v secondary.
 
adavey said:
Is the incoming service 480V delta or wye ?????? You might only have 3 conductors feeding the primary side of that transformer for a 110/208v secondary.
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I agree... mak134 should check the service voltage and configuration before buying the correct step-up transformer. That is, if he hasn't already. Perhaps he has and that is the reason for posting his question.
 
Correction to my earlier post, the last sentence should have read, "If you only needed a Delta/Delta you could back feed the transformer if the manufacturer blessed it, but do to inrush problems it is not recommended."

I had to answer the phone while I was finishing the post and was stuck in the "wye" mode I guess.

Roger
 
Wouldn't a 208/120-Y to 480/277-Y (or even a 480/277-Y to 208/120-Y used backwards) transformer be better than a 208-Delta to 480/277-Y unit? In other words, if the primary supply has a neutral, shouldn't it be used?
 
LarryFine said:
Wouldn't a 208/120-Y to 480/277-Y (or even a 480/277-Y to 208/120-Y used backwards) transformer be better than a 208-Delta to 480/277-Y unit? In other words, if the primary supply has a neutral, shouldn't it be used?
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If you have a wye primary, the transformer will let triplen harmonics flow into the primary. That is one major reason for delta primaries.

Jim T
 
jtester said:
If you have a wye primary, the transformer will let triplen harmonics flow into the primary. That is one major reason for delta primaries.
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I see, said the blind man. :cool:
 
Installation cost would be higher for a wye wye (extra conductor possible larger conduit), anditionally I would bet a wye wye would cost more, not a stock item in smaller sizes (just assuming the second thought).
 
I am wondering why there is no mention of a zig zag derived neutral from the Delta side in this thread. What is the intended 277V load?
 
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