Zigzag transformer

The purpose of a zigzag transformer in this application is to provide a return path for earth faults on delta-connected systems.

With negligible current in the neutral under normal conditions, an undersized (unable to carry a continuous fault load) transformer may be used only as short-time rating is required, provided the defective load will be automatically disconnected in a fault condition.

Impedance can be added after the secondaries are summed to limit maximum fault currents (the 3Io path).

[6] A combination of Y (wye or star), delta, and zigzag windings may be used to achieve a vector phase shift.

This also protects the switching devices inside the inverters, which are usually insulated-gate bipolar transistors (IGBTs).