A zigzag transformer has no secondary winding, and is
designed to provide a low-impedance path for the zerosequence
currents to flow. During a line-to-ground fault
condition, the zero sequence currents can flow into the
ground at the point of the fault, and back through the neutral
of the grounding transformer. The impedance of the zigzag
transformer to balanced three-phase voltages is relatively
high, therefore, when there is no fault on the system, only a
small magnetizing current flows in the windings. A zigzag
grounding transformer provides a stable neutral point which
makes possible its use for grounding an otherwise isolated
neutral system.