High voltage direct current (HVDC) transmission has come of age. The technology pioneered by ABB was first used half a century ago to bring power from the Swedish mainland to a remote Baltic island.
In 50 years HVDC has evolved from a pioneering technology to a well proven, effective and economic method of transmitting power over long distances. The first ever HVDC connection has recently celebrated its fiftieth anniversary. The story is one of unending development.
Fifty years ago the world’s first high voltage direct current (HVDC) link was inaugurated between the Swedish mainland and the Baltic island of Gotland. The new power connection not only brought down costs for consumers, it opened up a new era for the island’s economy.
Gotland lies 80km off the east coast of Sweden. It has an area of 3,140 sq km and a population of more than 57,000 people. The main industries are agriculture, fishing and tourism.
The advent of power from the mainland was sponsored by the Swedish government in a bid to reverse worrying trends in unemployment and a declining population. The technology chosen was HVDC delivered via a 90km, 100kV, 2MW submarine cable.
HVDC has proved itself in this and subsequent installations as an ideal vehicle for bulk power transmission and interconnecting independent power grids. HVDC lines cannot be overloaded, and so protect grid reliability and eradicate the ‘loop flows’ found in AC systems.
ABB pioneered HVDC with the Gotland link and has gone on to supply more than half of all the HVDC converter stations installed over the years. ABB has an installed transmission capacity of about 40,000MW out of a world total of 70,000MW.
Apart from the first installation, ABB has created the highest voltage HVDC link, the longest HVDC lines, above and below ground, the highest converter power rate and the longest submarine cable.
ABB’s unique HVDC Light, the latest patented innovation, is designed for underwater and underground transmission. The technology relies on voltage source converters and cables and its first installation was made in 1997.
STEPPING UP THE POWER
For Gotland, the first submarine cable was laid in 1953 between Västervik on the mainland and Ygne a town 10km south of the island’s capital, Visby. The power connection commenced with a rated voltage of 100kV and a transmission capacity of 20MW. In 1970 the stations were supplemented with thyristor valves, connected in series with the mercury-arc valves. This made it possible to raise the voltage to 150kV and the transmission capacity to 30MW.
In 1983 a new cable was laid providing a rated voltage of 150kV with a 130MW transmission capacity. The converters were built up of thyristor valves. The two connections operated independently. This additional power meant that all the islands’ needs could be supplied by the link and the local power station closed.
The third connection, planned in 1985, anticipated demand for 147MW. This is usually used in conjunction with the second link to form a bipolar link but can also also operate independently.