Characteristic and influence analysis on the inrush current of HVDC converter transformer

For HVDC converter station, a 12-pulse converter transformer is composed of six single-phase two-wing transformers generally, which are connected as Y0, y and Y0, d11 3-phase structure respectively. The two 3-phase transformers are parallel accessed to AC bus. Combined with the building and analyzing on the electric equivalent circuit, the theory researching on mechanism and characteristic of zero-sequence inrush current as 12-pulse converter transformer energizing in detail, and the distribution principle of the zero-sequence inrush current is laid out. With an energizing failure event of converter transformer in Zhengping converter station of ±500kV Three-Gorges HVDC project, the conclusion on zero-sequence inrush current of converter transformer is verified, which can explain the cause of converter transformer protection tripping.