Dry type cast resin transformer The windings of three phase transformers may be connected in by Y or Δ in the same manner as for three single phase transformer.Since the secondary’s may be connected either in Y or Δ regardless of which connection is used on the primaries, there must be four ways of connecting the windings of a 3-phase transformer for transformation of 3-phase voltages, namely Y-y,Δ -Δ, Y-Δ, and Δ -y.The inter-connections are made inside of the case so that only the terminal leads need to be brought outside the case:Star – Star Transformer (Yy0 or Yy6)Delta – Delta Transformer (Dd0 or Dd6)Delta – Star Transformer (Dy)Star – Delta Transformer (Yd) (Grounding Transformer)Zig-zag Transformer (Yz, Dz) (Grounding Transformer)Scott (“T” Type) Transformer (Grounding Transformer) 1. Star-Star (Y-y) ConnectionStar-Star (Y-y) Transformer Connection In Primary Winding Each Phase is120°electrical degrees out of phase with the other two phases. In Secondary Winding Each Phase is120°electrical degrees out of phase with the other two phases.Each primary winding is magnetically linked to one secondary winding through a common core leg.
