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Grounding transformer is referred to as grounding transformer for short. According to the filling medium, grounding transformer can be divided into oil type and dry type; According to the number of phases, the grounding transformer can be divided into three-phase grounding transformer and single-phase grounding transformer.

Single phase grounding transformer: single phase grounding transformer is mainly used for neutral grounding resistance cabinet of generator and transformer with neutral point, so as to reduce the cost and volume of resistance cabinet.

Three phase grounding transformer: when the neutral point of the system is △ type wiring or Y-type wiring and cannot be led out, the neutral point is led out for adding arc suppression coil or resistance. This kind of transformer adopts Z-type wiring (or zigzag wiring). The difference from ordinary transformer is that each phase coil is divided into two groups and wound reversely on the magnetic column of this phase. The advantage of this connection is that zero sequence magnetic flux can flow along the magnetic column, The zero sequence magnetic flux of ordinary transformer flows along the magnetic leakage circuit, so the zero sequence impedance of Z-type grounding transformer is very small (about 10 Ω), while that of ordinary transformer is much larger. According to the regulations, when using ordinary transformer with arc suppression coil, its capacity shall not exceed 20% of the transformer capacity. Z-type transformer can be equipped with arc suppression coil with 90% - 100% capacity.