Zig Zag Transformer

[Jerry123]

I have a question regarding a ground application on a delta system. We bought a High Resistance Grounding system. We had a choice for a Wye(broken)-Delta or Zig-Zag transformer to create the neutral point. We chose the Zig-Zag for the added benefit of harmonics.

When we receive the unit we found that the manufacture uses 3 individual single phase transformer for the zig-zag circuit. An issue that was brought up that is above my knowledge level is a concern that the unit will not operate properly because (bare with me) something to do with the Flux resistance/impedance through the air because of the single phase transformers. The proper application 3 phase zig zag transformer with common iron core and not three single phase transformers.

I hope someone can shine some light on the subject.

 

[DHambley]

I'm guessing that they used single transformers for the outriggers of the zig-zag to get a turns ratio which they couldn't get from a single 3 phase core. I see no reason that these single transformers should have any problems coupling flux from one winding to another. It's all vector addition.

 

[7anoter4]

I think it is about shell transformer-5 columns 3 phases-which presents less magnetic flux leakage and so a reduced reactance. A usual 3 columns transformer reactance will be not so reduced.

 

[waross]

A three legged three phase transformer does not have a path for unbalanced flux. This is not an issue with single phase transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[prc]

Three single phase transformers with zig-zag connections should work perfectly well as a three limbed three phase transformer. Since the rating of grounding transformer is so small, 3 phase construction is normal, but I dont find any issue with three single phase transformers with correct connections between windings.