GotLight, Sweden

Breezy southern Gotland was an early favorite for wind power. By the late 1990’s, the Swedish island had an installed wind power capacity of 40 MW (megawatt). To cope with additional wind power generation, the island grid needed an improved way of maintaining power quality. In addition, the local utility GEAB (Gotlands Energi AB) experienced difficulties acquiring the necessary permits to build an additional overhead power transmission line.

After a series of studies, GEAB was encouraged to build a pioneering HVDC (high-voltage direct current) commercial power transmission link called GotLight. The HVDC technology has the ability to overcome power quality problems that are inherent in wind power generation, and to transmit the power via underground cables. GEAB is a subsidiary of Vattenfall AB, which decided to finance the project together with the Swedish National Energy Administration.

There were many reasons behind their choice. Underground cables are environmentally friendly, easy to install and do not affect areas of natural beauty. Storms, falling trees, ice and snow cannot damage underground cables, and the land can be used for other purposes. Furthermore, the HVDC cables do not require maintenance and do not cause higher electro-magnetic fields normally associated with AC cables.

The project included project management, design, engineering, manufacturing, installation and commissioning, where all phases were completed successfully.

It was the world’s first extruded cross linked polyethylene (XLPE) insulated HVDC underground cable. The innovation gave the 80 kV cables enhanced mechanical strength and flexibility, making them ideal for tough installation conditions as well as for interconnecting grids to improve the stability of transmission networks. The cables could be plough installed in a cost-efficient manner and buried close to each other.

We made sure all the 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. A special advantage of the bipolar cable system used is the virtual elimination of all magnetic fields. The magnetic field is actually reduced to 1 % of the natural magnetism.

The transmission link between the wind farm in the southern part of Gotland and the city of Visby has a 50 MW power rating and it has been transmitting renewable power since 1999.

By providing this powerful solution, we made sure Gotland can continue on it's green path.