ABSTRACT
The first commercial high-voltage direct-current (HVDC) power transmission system was commissioned in
1954, with an interconnection between the island of Gotland and the Swedish mainland. It was an undersea
cable, 96 km long, with ratings of 100 kV and 20 MW. There are now more than 50 systems operating
throughout the world, and several more are in the planning, design, and construction stages. HVDC
transmission has become acceptable as an economical and reliable method of power transmission and
interconnection. It offers advantages over alternating current (ac) for long-distance power transmission and as
asynchronous interconnection between two ac systems and offers the ability to precisely control the power
flow without inadvertent loop flows in an interconnected ac system. Table 3.1 lists the HVDC projects to date
(1995), their ratings, year commissioned (or the expected year of commissioning), and other details. The
largest system in operation, Itaipu HVDC transmission, consists of two ^600-kV, 3150-MW-rated bipoles,
transmitting a total of 6300 MW power from the Itaipu generating station to the Ibiuna (formerly Sao Roque)
converter station in southeastern Brazil over a distance of 800 km.
