The function of grounding transformer is to draw the neutral point used for connecting arc suppression coil or resistance when the neutral point cannot be drawn out in the system with delta connection or Y type connection. This type of transformer adopts Z type wire connection and the difference between ordinary transformer is that coil of each phase is divided into two groups, respectively reverse around the magnetic column. The benefit of such connections is that zero sequence magnetic flux can flow along the magnetic column. However for ordinary transformer, zero sequence magnetic flux flows along the leakage magnetic circuit. So that the zero sequence impedance of Z type grounding transformer is very small (about 10 Ω ) ; however, for ordinary transformer, the zero sequence impedance is relative much bigger.