In a 120/240-volt, 3Ø, 4-W open-delta bank delivering power, the line current equals the winding current.

In a 120/240-volt, 3Ø, 4-W open-delta bank delivering power, the line current equals the winding current.

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

Answer: (A)

In an open-delta bank, two transformers are arranged to supply three lines without forming a complete closed delta. The external line currents flow directly through the windings that connect each line, so the current in each line is carried by the winding it connects to. With balanced loading, this means the line current has the same magnitude as the winding current. That’s why, for a 120/240-volt, 3Ø open-delta bank delivering power, the line current equals the winding current. The familiar sqrt(3) relationship appears in a full delta (where line current is sqrt(3) times the winding current) but does not apply to this open-delta configuration.

In an open-delta bank, two transformers are arranged to supply three lines without forming a complete closed delta. The external line currents flow directly through the windings that connect each line, so the current in each line is carried by the winding it connects to. With balanced loading, this means the line current has the same magnitude as the winding current.

That’s why, for a 120/240-volt, 3Ø open-delta bank delivering power, the line current equals the winding current. The familiar sqrt(3) relationship appears in a full delta (where line current is sqrt(3) times the winding current) but does not apply to this open-delta configuration.