This circuit simulates transmission of AC as well as DC power via same 3 phase transmission line. It superimposes DC onto AC via primary Delta and secondary Zig-Zag transformer neutral and obtains DC current at other end of line via Zig-Zag neutral of Zig-Zag-Delta transformer. It has several advantages where of of the main advantage is line is utilised to its full capacity and aslo AC stability margins are unaffected by introduction of DC power
