Three-phase Earthing Transformer

This type of transformer adopts a Z-connection (or zig-zag connection). The difference from a conventional transformer is that the coil of each phase is divided into two groups and wound in opposite directions on the magnetic core column of the corresponding phase. The advantage of this connection is that the zero-sequence magnetic flux can flow along the magnetic core column, whereas the zero-sequence magnetic flux of a conventional transformer flows along the leakage magnetic circuit. Therefore, the zero-sequence impedance of a Z-connection earthing transformer is very small (approximately 10Ω), which is much lower than that of a conventional transformer.

In accordance with the specifications, when a conventional transformer is equipped with an arc suppression coil, the capacity of the coil shall not exceed 20% of the transformer's rated capacity. In contrast, a Z-connection transformer can be equipped with an arc suppression coil with a capacity accounting for 90% to 100% of its rated capacity. Besides being fitted with an arc suppression coil, an earthing transformer can also supply secondary loads and serve as a station service transformer, thereby reducing investment costs.