Open Delta Transformer Connection – Calculation & Diagram Connection Diagram of Open Delta Transformer. The above figure shows the connection diagram of an open delta system. In this diagram, a three-phase unity PF load (resistive load) is supplied by two transformers. Each transformer is rated as 10 kVA (current rating is 10 A and voltage rating is 1000 V). Transformer Connections: Phase Shift - Voltage Disturbance Delta Wye or Wye Delta Transformer Phase Shift. We know that across a delta-wye (star) or wye- delta transformer there will a 30-degree phase shift between line voltages. With this there are two options: delta could lead the wye side by 30 degree or wye side could lead the delta by 30 degrees.