Due to the serious imbalance of the secondary load of traction transformer, the negative-sequence current in the three-phase side is large, which inhibited the development of the technology of taking power from traction network. The negative-sequence current characters of power transformer for railways of five connection types by symmetrical component method, including D,y11, D,d0, Y,y0, Y,d11 and Reverse-Scott is discussed in this paper. Moreover, an improved Reverse-Scott connection type is proposed to reduce the unbalanced degree.

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