Transformer rewire calculations- wye to delta

[ShawnK]

I have a three phase 15kVA transformer that is wired in a wye to wye configuration. The primary is expecting 115V L-N (199V L-L) and is rated to output 240V L-N (415V L-L) on the secondary. I was told by a major industrial power controller company that I could use their 240V L-L equipment on the output of this transformer only if I did not connect the neutral (on the secondary) to anything. This statement does not give me a warm fuzzy.

I was also wondering if there is a way to calculate what the output voltage would be if the secondary was re-wired to a delta configuration. I am happy to do the calcs myself if someone can point me in the right direction.

 

[dahualin]

What is the power requirement of the equipment? If it requires 240 volt single phase only, I don't think it is a problem to connect to the transformer that can provide 240 volt (L-N). If it requires 240/120 volt that means it needs 120 volt power also, the transformer will not work.

David

 

[Smart $]

Reconfigured to Delta would yield .58 times the voltage of the Wye configured secondary, i.e. 240 volts L-L.

 

[LarryFine]

Maybe I'm missing something, but if the secondary windings are 240v-Y line-to-neutral, you could just rewire them into a Delta configuration.

The only concern would be deciding whether to ground a phase. I would, unless the equipment supplied needs floating (ungrounded) Delta.

 

[don_resqcapt19]

I've never seen a three phase transformer that could be rewired to change
from wye to delta.
Don

 

[cpal]

is this a three phase transformer? or a three phase bank. (three single phase transformeres configed for three phase.

http://www.allaboutcircuits.com/vol_2/chpt_10/5.html

charlie

 

[ShawnK]

OK, I'll try to get all the answers in. The load is a liquid heater that can consume up to the full 15kVA. There is a power controller that modulates the power to the load through some kind of solid state relay. I don't think you could ground one of the phases or the controller would not function correctly.

The transformer appears to be a three phase bank, that is, there is available two conductors for each primay and secondary on each transformer in the bank, but all the transformers share a common core.

 

[LarryFine]

I've never seen a three phase transformer that could be rewired to change
from wye to delta.

Aren't the primary and secondary connections to each of the three sections in a single 3-phase transformer accessible, and re-connectable?

 

[iwire]

Aren't the primary and secondary connections to each of the three sections in a single 3-phase transformer accessible, and re-connectable?

Not in any that I have seen.

They are soldered or welded connections, not the kind of field modification that I would undertake. (Unless it was for my own house )

 

[ShawnK]

On my transformer, thankfully, all the transformer connections have soldered ring terminals attached, and the neutral connections (in the current Y config) are made with jumper that can be unbolted and rearranged. After checking out the link that cpal posted, I am pretty confident that I can reconfig the secondary as a delta and achieve the 240V L-L that is desired. I just had to draw it out and realize that a 240V secondary winding is not going to have the voltage across that winding change regardless of the configuration it is in. Then the differences between the Y and delta config become obvious.

Thanks for the help! And especially please correct me if I am making some bad assumptions.