Below is a photo of two-circuits of a 220 MW, +/- 350 KV High Voltage DC (HVDC) Leyte – Luzon transmission line in the Philippines. Unlike the AC transmission and tower structure which has three (3) sets of wires for the three-phases (Phase A, Phase B, and Phase C) per circuit, the HVDC has only one set of wire per circuit.
HVDC transmission system is usually used for transmitting power between very long distances because it has lower line losses and higher power transfer capacity with the same size of wire as the HVAC line. Also, you don’t have to worry about the EMF radiation (if this is indeed an issue) in HVDC. The problem with DHVC is that you have to install an DC-AC and AC-DC converter/inverter in both ends.
More info here: http://www.jcmiras.net/jcm/item/86/