## Transformer vector group Dyn11 and Dyn1

what the difference between transformer Dyn11 and Dyn1

i know the difference is in leading and lagging of line to line voltages of primary and secondary

but the question is , when i should use Dyn11 or Dyn1 as a must in the network

does it depends on the type of load ?

all what i know that in parallel operation the 2 transformers must be exactly the same ,

but what according to what in the first place we choose Dyn1 or Dyn11

anybody have an idea ???

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 what the difference between transformer Dyn11 and Dyn1
According to most standards transformer coils are classed as either Delta (D), Wye (Y) or Zigzag (Z).

Dy11 signifies a Delta Primary (primary has an upper case letter), Wye secondary (secondary has a lower case letter) and the orientation of the 3 phase diagram, relative to the A phase on a clock face pointing to 11 o'clock.

So draw 3 vectors 120 degrees apart to represent the 3 phases, but start with your reference phase (A phase) at 11 o'clock.

Dy1 would hence be a Delta primary, Wye secondary and a vector diagram with the reference vector pointing at 1 o'clock.

I believe most 3 phase textbooks have the vector diagram with the reference vector at 0 degrees on the x-axis, which would equate to 3 o'clock, then with B at 11 o'clock and C at 7 o'clock.

 but what according to what in the first place we choose Dyn1 or Dyn11
Any combination of a Delta coil and a Wye coil (Dy or Yd) will cause a phase shift by +/- 30 degrees. Therefore we use another Delta coil and Wye coil combo to shift it back to whatever is desired.

And yes, if you want to parallel transformers they have to be of the same vector group or you will have circulating currents and associated problems.