A 120/240-volt, 3Ø, 4-W open-delta bank delivers power to a load. The line current equals ___.

A 120/240-volt, 3Ø, 4-W open-delta bank delivers power to a load. The line current equals ___.

• A. Icoil (or winding)
• B. Icoil (or winding) × 1.732
• C. Icoil (or winding) ÷ 1.732
• D. Icoil (or winding) × 0.5

Answer: (A)

Open-delta uses two transformers arranged in a V, not three in a closed delta. In this setup, each line current flows through the winding connected to that line, so the line current equals the current in the corresponding coil. The familiar √3 relationship that appears in a full delta doesn’t apply here, because there isn’t a third winding to contribute to the line current vector sum. Balanced load conditions give equal coil currents, and those currents appear directly as the line currents. That’s why the line current is simply Icoil.

Open-delta uses two transformers arranged in a V, not three in a closed delta. In this setup, each line current flows through the winding connected to that line, so the line current equals the current in the corresponding coil. The familiar √3 relationship that appears in a full delta doesn’t apply here, because there isn’t a third winding to contribute to the line current vector sum. Balanced load conditions give equal coil currents, and those currents appear directly as the line currents. That’s why the line current is simply Icoil.