Your query Dy11 with reference to tranmsformers, It is connected with 3 phase transformers the way phases are connected, in primary and secondary. In this case
Primary is connected in delta with R phase in 12 O clock position and the secondary is connected in star , such that the R phase has a shift of 30 degrees advance, ( positive direction is anti clock wise) and shown by 11 O clock position.
This is very common type of connection and is used often with step down transformers.
vector group
Re: vector group
