Wondering what are important factors when specifying the vector group for a 25kV/690V transformer (approx 3MVA) for industrial process. Both primary and secondary systems are insulated neutral. Does phase shift matter? What is normal for a transformer of that size? Yy0?

 

Responding to mim's Aug 23, 6:00pm query... your proposal intrigues me:

By definition the Yy0 connection, European practice, has 0°-phase shift between the primary and secondary winding. (In the USA, it is possible to have a 180° phase shift.)

Hopefully, you are aware that use of the Y-Y connection is unusual. The most frequent problem is neutral instability. Such behavior is influenced by load variation, as well as the condition of the supply neutral, i.e., earthed or not.

Can you provide some additional details?

Regards,
Phil Corso, PE {Boca Raton, FL, USA}
[[email protected]] ([email protected])