Z-circuit

In the Z circuit, an input or output winding of a three-phase transformer is distributed over two coils. The magnetic coupling with two phases creates a balancing effect that distributes very different phase currents more evenly and reduces voltage differences. The Z-connection requires around a third more power than a delta or star connection. With this and the additional wiring effort, this type of circuit only makes sense if its advantages are really needed.

For further information, see switching group