Zigzag transformer
A zigzag transformer uses a special winding arrangement called a zigzag or interconnected star. Each output voltage is the vector sum of two phases that are offset by 120°. This winding is used for grounding, reducing certain harmonics, and providing non-isolated, phase‑shifted 3‑phase power.
How it works: the windings are split into three limbs, and each limb has two halves wound in opposite directions. The first coil on one core connects to the second coil on the next core, and the second coils are tied together to form a neutral. The three phases connect to the primary windings. In normal operation the voltages cancel in the neutral, so little current flows there. The zigzag arrangement gives the transformer a high positive/negative sequence impedance but a low zero‑sequence (ground) impedance, which can be tied to earth when needed.
In fault conditions, such as a phase-to-ground fault, the zigzag provides a path for fault current to return to earth, helping stabilize the system. The neutral is normally near ground, and a transformer can be used with relatively small insulation for short fault events if the faulty load disconnects automatically. The impedance can be set to limit fault currents after the secondaries are summed.
Zigzag windings can be combined with other winding types (Y, delta) to create different phase shifts. This is useful for linking networks like a high-voltage star/star network to a distribution delta/star network, or to provide an earth reference when a delta-connected leg lacks one. Utilities often use zigzag transformers when connecting three-phase inverters to the grid, to maintain a stable neutral voltage and protect switching devices in the inverters.
This page was last edited on 3 February 2026, at 07:51 (CET).