The new underground cable connection to the main grid is the first 400 kilovolt cable in history to be made this long in Helsinki.
When completed, it will run for 12 kilometres from the Länsisalmi substation in Vantaa to the new Vanhakaupunki substation in the Viikinranta Energy Block in Helsinki. The cable connection is created in collaboration between the City of Helsinki, Helen Sähköverkko and Fingrid.
Project planning began in 2020, and constriction work began in 2024. The cable will be operational in 2026.
“There are many different sites and challenges along the route, which have been solved in collaboration with the City of Helsinki, the authorities, stakeholders and various experts, among others. Discussions have been and are still actively taking place, for example, regarding archaeological areas and nature objects along the cable route. It has also taken over a year to get landscape work permits in the Helsinki area,” says Project Director Risto Ryynänen from Fingrid.
For example, in the Kivikko cultural history area, an archaeologist reviewed and mapped the location of bunkers and cannons from World War I which the cable passes under.
Nature values are considered particularly important in the planning of the route, and various experts, for example Helsinki Nature Conservation Association, have been consulted on the matter.
“We have prepared nature reports and made ground surveys, especially in the areas of the Kivikko forest, Hallainvuori and the fields of Viikki.”
The cost of the investment in the entire project is over EUR 100 million.
When building an underground cable in an area of dense infrastructure, it is necessary to pass through many traffic thoroughfares by horizontal drilling under them.
“This has not been done to this extent before,” Ryynänen points out.
In this project, the largest horizontal drillings are under the Porvoo motorway, Vantaa tram, Maratontie, Ring I and the light rail line on Viikintie. In addition, a rock borehole about 360 metres long passes under the cultural history area in Kivikko. There are horizontal drillings in eight locations.
“A number of temporary routes are also being made to the installation sites as the work progresses, so that, for example, people can safely travel around the area for recreational purposes,” Ryynänen explains.
The project has progressed according to schedule despite a variety of challenges. The construction of the cable route is nearing the end, and the substation contracts are already topping out. Installation of the cables will begin during the spring and summer of 2025.
