Which statement best describes how LV line currents relate to HV line currents in a delta-wye transformer?

Which statement best describes how LV line currents relate to HV line currents in a delta-wye transformer?

• A. LV line currents are equal to HV line currents in magnitude.
• B. LV currents are the same as HV currents but shifted by 30 degrees.
• C. LV line currents are related by the winding connections and phase displacement, not simply equal.
• D. LV currents are always zero when HV current is nonzero.

Answer: (C)

In a delta-wye transformer, you can’t expect the LV and HV line currents to be simply equal. The currents on each side are tied to the winding connections and the phase relationships between the windings, plus the turns ratio. On the low-voltage side, which is configured as wye, each line current essentially flows in its corresponding LV winding. On the high-voltage side, the delta connection means each line current is a vector combination of the currents in two delta windings and carries a 30-degree phase relationship with the primary voltages. The turns ratio sets the overall magnitude scale, but the actual line currents on the two sides are modified by these geometry and phase-shift effects. So the correct idea is that LV line currents relate to HV line currents through the winding connections and the resulting phase displacement, not by a simple equality.

In a delta-wye transformer, you can’t expect the LV and HV line currents to be simply equal. The currents on each side are tied to the winding connections and the phase relationships between the windings, plus the turns ratio.

On the low-voltage side, which is configured as wye, each line current essentially flows in its corresponding LV winding. On the high-voltage side, the delta connection means each line current is a vector combination of the currents in two delta windings and carries a 30-degree phase relationship with the primary voltages. The turns ratio sets the overall magnitude scale, but the actual line currents on the two sides are modified by these geometry and phase-shift effects.

So the correct idea is that LV line currents relate to HV line currents through the winding connections and the resulting phase displacement, not by a simple equality.