Overhead transmission lines for HVDC

Many classical HVDC systems use overhead transmission lines. In most cases, this is due to very high power transmissions and long distances, approximately 600 km or more, usually from remote power generating stations.

HVDC is well suited for such applications, since the cost is lower than it would be for similar AC transmissions. A DC line needs only two main conductors, while an AC line needs three, and DC electrical losses are lower. HVDC converter stations do cost more than the AC terminal stations, so a certain distance is required in order for an HVDC system to make economic sense.

Long distance HVDC applications using overhead lines are found around the world, in the USA, Canada, Brazil, China and India.

The figure below compares the Three Gorges-Shanghai power transmission as an AC and a DC transmission system. The top line shows two 3,000 MW HVDC lines, compared to the five 500 kV AC lines (below) that would have been needed if AC transmission had been selected to deliver the same amount of power. HVDC transmission systems clearly have far smaller footprints than AC systems.