What are the differences between the Wye Primary and Wye Secondary Medium voltage transformers and 5 legged Cores on Medium voltage Transformers?

Issue:
Does a 5 legged Core Medium voltage transformer isolate the Primary and secondary of Powercast Medium voltage transformers as Terciary wound MV transformers?

Product:
MV Powercast Transformer

Environment:
Application

Cause:
Product Features

Resolution:
Normal delta -wye transformers only require a 3-legged core.
For wye-wye transformers:

• There can be stray flux heating during unbalanced loading which is why we provide a 4-legged or 5-legged core.  The extra core leg provides a return path for the flux.  This is standard on ALL wye-wye transformers we build.

• Similarly, a buried tertiary winding provides a path for the balancing current to flow when the secondary must supply an unbalanced load.   A buried tertiary winding is usually only used to accommodate unbalanced loads but can be brought out to a set of external bushings to provide external power.

Released for: Schneider Electric USA