short circuit current

[tulum]

Does the short circuit current change at all if 3 single phase transformers are used connected in delta - wye vs. one standard 3P delta wye transformer?... assume 2.5% impedance typical...

Regards,
TULUM

 

[dpc]

Not if the impedances and kVA ratings are equivalent.

 

[davidbeach]

As dpc said, if you have a transformer of a given kVA (MVA) rating and impedance, and you put it in a box, there are no simple tests to determine if it is a single three-phase transformer or three single-phase transformers. Some very sophisticated zero sequence impedance testing might discern a slight difference.

 

[rbulsara]

In fact electrically a 3ph transformer is nothing but three single phase transformers in a box. The economic savings are due to shared cores and lesser space/weight requirement.

 

[dpc]

There could be some differences in the zero sequence impedances, depending on the construction of the three-phase transformer.

 

[waross]

Are core form three phase transformers still being made. That is, three legged cores.
I understand that three legged three phase transformers are intolerent of unbalanced loads. If the loads are not balanced, there is no return path for the unbalanced flux and it has to return through either the air or through the core supports and the housing.
Any comments on this?
respectfully

 

[davidbeach]

waross, yes they are, but they include a buried delta tertiary if they are wye-wye. Apparently it is less expensive to build a 3 legged core wye-wye and include the tertiary than build a 4 or 5 legged core, gotta watch the manufacturer and make sure your specs are clear if you don't want that tertiary. With a delta primary or secondary (or both) three legged cores are common.

 

[waross]

Thanks David
Respectfully