This is a scott connection which convert 3 phase and 2 phase & vice versa if employs two identical transformers one with centre tap primary known as main transformer and the other with primary √ 3/2 tap known as teaser transformer . the main transformer primary centre tap D is connected with one end of the teaser primary as shown in the figure .
Now ends A, B, C, are connected to three phase ac supply and two phase four wire supply is obtained.
The two phase side makes use of all the turns on teaser winding as well as all the voltage per turns of the two transformer to be equal.
The voltages in the primaries of two transformer are 90 (degree) phase displaced . So voltages in there secondary voltages will also 90 (degree) displaced i.e. 3 phase supply has been converted to 2 phase.If we interchange the position the load and supply 2 phase can be converted into 3 phase.