Conversion of AC transmission lines to HVDC using current modulation

This paper outlines a method for modulating direct current in such a way as to distribute power equally among three rather than two conductors., thus making it particularly adaptable to conversion of long AC lines to HVDC. Those principles and the resulting operating characteristics of "tripole" HVDC are then discussed as they relate to converter station design, construction and operation. Finally, the operating characteristics which distinguish tripole HVDC are compared to traditional monopole and bipole schemes as they bear on the value-in-service of an HVDC line. It is shown that the tripole scheme will often be less costly, more reliable and easier to adapt to high overload capacity than traditional schemes, that it may allow increased loading on parallel ac circuits, and that it can be achieved using equipment and operating techniques already proven in hundreds of existing HVDC installations