The HVDC link to Gotland is the dominating source of electric power.
The island of Gotland was originally self-sufficient as regards electric energy. A thermal power station in Slite catered for the needs of the entire island. However production costs were relatively high and tariffs were double those on the Swedish mainland. It was therefore expensive to run industries on Gotland and there were problems with unemployment and depopulation.
In order to break this trend the Swedish parliament decided in 1950 to finance a transmission link from the mainland to Gotland. This link would make it possible to satisfy a greater demand for electricity and at the same time reduce the tariffs. The transmission was to use HVDC due to the long distance (100 km) across the sea.
Gotland 1
The submarine cable was laid in 1953 between Västervik on the mainland and Ygne, 10 km south of Visby on Gotland. In 1954 operation could begin with rated voltage 100 kV and transmission capacity 20 MW. It was the first commercial HVDC transmission in the world.
In 1970 the stations were supplemented with thyristor valves which were connected in series with the mercury-arc valves. This made it possible to raise the voltage to 150 kV and the transmission capacity to 30 MW. It was the first time thyristor valves were used in a commercial HVDC transmission in the world.
Read more in about Gotland 1 in: The early HVDC development
Gotland 2 and 3
In 1983 a new cable was laid between Västervik and Ygne. The rated voltage was 150 kV and transmission capacity 130 MW and the converters were built up of thyristor valves. Gotland 2 and Gotland 1 operated independently of each other and it was now possible to satisfy the entire electrical demand on Gotland with power from the mainland via the links. The oil-fired power station in Slite and the diesel sets in Visby could therefore be stopped to function as reserves.
In 1985 an electricity demand of 147 MW was registered on Gotland and it was assumed that demand would increase further. In order to meet the greater demand and also to increase the safety of supply to the island, a decision was taken to invest in yet another HVDC link, Gotland 3.
The total transmission capacity is thus 260 MW (max. 320 MW).
The original cable and terminal equipment for Gotland 1 has been taken out of service and dismantled.