Principles and applications of current-modulated HVDC transmission systems

This paper reviews, from an application perspective, a method for operating parallel bipole and monopole system in such a way as to use all three conductors of a converted three phase ac line while eliminating the need for ground return current. The characteristics of the resulting "tripole" HVDC scheme are discussed as they relate to system operating needs, including increases in fine rating, reliability, dynamic support and ice inhibition. It is shown that when converting an ac line to HVDC the tri-pole scheme will usually be less costly, more reliable and easier to adapt to high overload capacity than traditional bipole schemes. It can be achieved using equipment and operating techniques already proven in hundreds of existing RVDC installations.