The Swedish island of Gotland is also the site of the world's first commercial HVDC Light transmission. HVDC Light is based on voltage-source converter (VSC) technology, which uses IGBTs (Insulated Gate Bipolar Transistors) to convert electrical current from AC to DC.
Breezy southern Gotland was an early favorite for wind power plants. By the late 1990s the island had installed wind power capacity of 40 MW. But to cope with additional wind generation capacity, the island grid needed an improved way to maintain power quality. In addition, there were great difficulties in getting the necessary permits to build an additional overhead transmission lines.
HVDC Light power transmission solved the problem with its ability to overcome power quality problems inherent in wind power generation, and to transmit the power via underground cables. This encouraged the local utility GEAB to decide to build the world’s first commercial HVDC Light transmission. GEAB is a subsidiary of Vattenfall AB, who financed the project together with the Swedish National Energy Administration.
The transmission link between the southern part of Gotland and the city of Visby is rated 50 MW and was put into operation in June 1999. Two 70 km long extruded 80 kV HVDC Light underground cables, buried close to each other, connect the stations. All equipment was mounted in enclosed modules in the factory and fully factory tested, so that civil works, installation and commissioning time was kept to a minimum.