Transformer Impedance

[robh]

I have three transformers fed from the utility. The secondaries of these x-formers feed our plant with 3 phase 480 volts. It is currently wired with a wye primary and a delta secondary. Does the impedance of the three transformers change depending on how they are hooked up? wye-wye, wye-delta, or delta-delta? Hope this makes sense.
Thanks

 

[jim dungar]

I have three transformers fed from the utility. The secondaries of these x-formers feed our plant with 3 phase 480 volts. It is currently wired with a wye primary and a delta secondary. Does the impedance of the three transformers change depending on how they are hooked up? wye-wye, wye-delta, or delta-delta? Hope this makes sense.
Thanks

No, the impedance is effectively per winding, regardless of the configuration.

 

[jtester]

The impedance of the system will change radically with changes in transformer connections. For example a grounded wye-grounded wye connection will have less L-G fault current because it "sees" the high side zero sequence impedance, whereas a similar sized delta-wye won't "see" the high side system impedance and will have a higher L-G fault current available.

Jim is correct that the transformer impedance won't change, but calculations relating to system impedance and available fault current will.

Jim T

 

[robh]

Thanks for the responses. I would have guessed that the impedance of the x-formers would stay the same, but I couldn't find any information looking around the web to support my thoughts.
Thanks again,
Rob