Unbalanced Transformer

quantum

Member
Location
LA
Are there any issues that can arise from unbalancing a three phase transformer if you never load it more than 33% of its rated output? We have a 480V Delta/240-120V Delta center tap transformer rated for 150KVA. We only need around 40KW from the 240-120V outputs.
 

gar

Senior Member
190605-1236 EDT

quantum:

You need to clarify your question.

I don't know what transformer is.

Is this one single phase transformer from 480 between two primary terminals and a single three terminal center tapped secondary? Or is it something else, like 2 or 3 single phase transformers operating in a 3 phase circuit to transfer 3 phase power from a 3 phase source to a 3 phase load.

Your question almost seems to imply some sort of 3 phase transformation thru 2 or 3 transformers to a wild leg delta.

If you do not exceed the current rating of any wire in your transformer, then it should not matter how the transformer is loaded. Thus, you should not overheat the transformer.

.
 

quantum

Member
Location
LA
190605-1236 EDT

quantum:

You need to clarify your question.

I don't know what transformer is.

Is this one single phase transformer from 480 between two primary terminals and a single three terminal center tapped secondary? Or is it something else, like 2 or 3 single phase transformers operating in a 3 phase circuit to transfer 3 phase power from a 3 phase source to a 3 phase load.

Your question almost seems to imply some sort of 3 phase transformation thru 2 or 3 transformers to a wild leg delta.

If you do not exceed the current rating of any wire in your transformer, then it should not matter how the transformer is loaded. Thus, you should not overheat the transformer.

.
It's a 3-Phase transformer. 480V Delta to 240V Delta (Center tapped on one coil for 120V).
 

gar

Senior Member
190605-1533 EDT

quantum:

Is this transformer really a single transformer with a single core, or is it really 2 or 3 single phase transformers wired to transform 3 phase?

A center tapped winding on a 3 phase delta generally implies what can be called a wild leg delta.

In any event no matter what the construction is the primary limitation is the maximum hot spot somewhere in the transformer or transformers, and that temperature is determined by power dissipated, and thermal transfer in the transformer. If the current rating on any winding exceeds the current you load to, then you should be safe. Obviously ambient temperature around the transformer must be below its rating. In the design of the transformer these items are part of the process.

.
 

quantum

Member
Location
LA
190605-1533 EDT

quantum:

Is this transformer really a single transformer with a single core, or is it really 2 or 3 single phase transformers wired to transform 3 phase?

A center tapped winding on a 3 phase delta generally implies what can be called a wild leg delta.

In any event no matter what the construction is the primary limitation is the maximum hot spot somewhere in the transformer or transformers, and that temperature is determined by power dissipated, and thermal transfer in the transformer. If the current rating on any winding exceeds the current you load to, then you should be safe. Obviously ambient temperature around the transformer must be below its rating. In the design of the transformer these items are part of the process.

.
I'm really curious if there are any issues that can arise from unbalancing the transformer. I don't think you are really answering my question. Like I stated above, I would not put more than 1/3 of it's rated capacity on the center tapped winding to feed a 240/120V panel, but I would have 0 load between the other windings. Besides heat, which should not be an issue since I'm keeping the load down, are there any other issues that can arise?
 

gar

Senior Member
190605-2032 EDT

quantum:

You list your occupation as PM. What is PM and what is your electrical background?

I may not be able in any to way answer your question, but it is not possible for anyone to answer your question without a definition of what your transformer is.

.


 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I would not put more than 1/3 of it's rated capacity on the center tapped winding to feed a 240/120V panel, but I would have 0 load between the other windings.
You should be fine. As long as you don't overload what you're using, the unloaded windings won't cause problems.

Any 240v loads that don't need the neutral can be wired to the high leg and either other leg to reduce the imbalance.
 

quantum

Member
Location
LA
190605-2032 EDT

quantum:

You list your occupation as PM. What is PM and what is your electrical background?

I may not be able in any to way answer your question, but it is not possible for anyone to answer your question without a definition of what your transformer is.

.


Not sure why it matters, but PM = Project Manager, I'm a physicist with a good electrical background, lots of theory and not so much practical application.
 

quantum

Member
Location
LA
You should be fine. As long as you don't overload what you're using, the unloaded windings won't cause problems.

Any 240v loads that don't need the neutral can be wired to the high leg and either other leg to reduce the imbalance.
Thanks Larry. I figured as much, but wanted a second opinion.
 
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