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Step-up transformer connection wye-star versus star-star

Step-up transformer connection wye-star versus star-star

Step-up transformer connection wye-star versus star-star

(OP)
I have a fleet of diesel generators, generating at 400V. I use these in different applications through step-up transformers. So I need flexibility to parallel with other systems at 11kV, 22kV etc. My current fleet of step-up transformers are star-star connected. The original transformer supplier mentioned something about 'no problems with 'phase displacement' if you go star-star. Now I have a client that wants the LV (400V) winding to be connected in delta and the MV connection in star (11kV), due to 'potential 3rd harmonics' if the LV is in star. IS star-star or delta-star the best for paralleled step-up transformers?

RE: Step-up transformer connection wye-star versus star-star

The 'best'? If only it was that simple!

Do you have to serve any loads requiring an LV neutral? You can provide much better protection on an LV delta system with a high resistance earth connection, but only if you don't need the neutral. You can also avoid any circulating current problems, especially if the machines are not closely matched, if you can live without the machine neutrals being connected to each other although you will still need to provide a single neutral-earth connection somewhere on the LV bus.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Step-up transformer connection wye-star versus star-star

With a star star connection any single phase load must be supported by one winding in the generator. With a delta, all three generator windings contribute to the support of a single phase load.
Our little utility ran for years with delta connected generators in parallel with wye connected generators, feeding a delta:wye transformer bank.  

Bill
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"Why not the best?"
Jimmy Carter

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