HVDC transmission systems use direct current instead of alternating current for the transmission of electricity. HVDC converters use high power thyristors for electricity conversion from AC to DC and vice versa.

Conventional HVDC applications include back-to-back interconnections of asynchronous networks and the overhead or submarine transmission of electricity over long distances.

In applications where load centres are located far away from energy resources, UHVDC transmission shows great superiority. Compared to a conventional ±500kV HVDC scheme, a ±800kV UHVDC scheme can reduce transmission losses of up to 60% and provide power capacities up to 8000MW and even more, almost doubling that of a ±500kV scheme. UHVDC is expected to play a major role in the future bulk power highway for smart electricity grids.