Basis of selection of Distribution Transformer Vector group

[alanElec]

I know i have been asking a lot about vector groups these days.The more I learn,more is the no of questions I have.Thanks u All for the knowledge sharing..

1.I think Dyn11 vector group is the most commonly used vector group in distribution transformers.This means the low voltage supply lags behind high voltage by 30 degrees.As per my understanding this is merely done to compensate for the Phase lead provided at the generation side by Yd1 step up transformer.

So y do we use Yd1 transfromer at the generator side at all?Cant we use Yy or Dd transformer at the gen side so that we can use a similar kind in the distribution side too??I mean the requirement is to just step up the voltage so that it can be transmitted over long distances.Why introduce a phase diff at the gen side?

I know this might include a lot of explanation and maths..I would be glad if any1 could give me an explanaion and a link for the math(i mean network analysis)

Regards,

Alan

 

[prc]

Large generator transformers are connected in Yd1 ( in US)or Yd11 (other places) so that 30 degree shift on output side is unavoidable. Delta connection is provided on LV side to prevent zero sequence currents entering in to generator windings on a LG fault on transformer HV side.Rotating machines cannot handle zero sequence currents and hence the need for this connection.

 

[davidbeach]

ANSI standard is that low side lags the high side by 30 degrees. Then there is no further worry. The rest of the world seems to evaluate transformer vector group transformer by transformer.