How does a delta-wye transformer affect line currents and phase angles?

• A. It introduces a 30-degree phase shift between HV and LV line voltages; currents are related by the winding connections.
• B. It eliminates any phase shift between HV and LV line voltages.
• C. It inverts line currents by 180 degrees.
• D. It doubles the magnitude of line voltages without changing phase.

Answer: (A)

A delta-wye transformer creates a 30-degree phase shift between the line voltages on the two sides because the windings are connected differently. With a delta primary and a wye secondary, the line-to-line voltages on the LV side are displaced by about 30 degrees from the HV line-to-line voltages. The size of the voltages follows the turns ratio, but the currents don’t simply mirror that relation in phase because the delta and wye connections handle currents differently. The current on one side is related to the currents in the windings as dictated by the winding configuration, which introduces the phase shift in the line currents as well. In short, the delta-wye setup produces a 30-degree shift in line voltages, and the line currents are related by the winding connections, not simply in-phase with the voltages.