Omexom in Finland to Deliver the Country’s First 400 kV Underground Power Cable to Helsinki

The project is part of a broader green energy transition in the Finnish capital, driven by national grid operator Fingrid in collaboration with the City of Helsinki and Helen Electricity Network (Helen Sähköverkko).

This 12-kilometer high-voltage connection, once completed, will significantly strengthen Helsinki’s power grid and facilitate a more sustainable energy supply by substituting coal-fired power plants with modern heat pump systems. Furthermore, it will enable the removal of existing 110 kV overhead lines along Vihdintie, one of the radial roads carrying traffic to and from the Helsinki metropolitan area, thereby helping to declutter the urban landscape. Removing 110 kV overhead lines and replacing them with cables is part of the project of transferring the road and area to city boulevard.

Omexom has been involved in this ambitious project since 2021, providing early-phase design support alongside engineering firm Ramboll.

The construction project delivery includes full management of the construction site and HSEQ (Health, Safety, Environment, and Quality), cable pulling, and site services. It also involves auxiliary tasks carried out by high-voltage specialists for accessories installation, along with support in cable project management to ensure smooth coordination throughout the process. Additionally, Omexom’s team has contributed to route planning and jointing section design, a critical phase for a complex infrastructure project of this scale.

As Helsinki moves away from coal-based energy, demand for electricity is rising rapidly, explains Ilmari Koikkalainen, Project Manager at Omexom in Finland.

Until recently, Helen relied on coal-fired plants for both electricity and district heating. Ilmari said, “With the closure of the Hanasaari plant in 2023 and shutdown of Salmisaari in April 2025, the shift to heat pump technology requires doubling the electrical supply to the city, hence the need for this 400,000-volt underground cable connection.”

The cable connection will play a key role in major urban developments like Western Boulevard City, a new district northwest of Helsinki designed for over 14,000 residents.

Building a project of this scale in a dense urban environment comes with significant challenges. “The size and weight of the 400 kV cables and the logistics of working within a busy city are major factors,” explains Ilmari. “We have transported 89 massive cable drums from the Port of Vuosaari to multiple construction sites across Helsinki.”

In addition to these logistical complexities, the rainy Finnish summers further presented challenges related to site water management. However, thanks to the high level of collaboration between the civil contractors and other stakeholders, the project team has been able to manage these issues effectively.

Despite facing several weather-related and landscape challenges, the project remains on track, and the teams are bracing themselves for approaching winter and low temperatures.

“We hope our performance on this flagship project positions us as a long-term partner for Fingrid in future 400-kV underground cable installations,” concludes Ilmari.

The project is also making strides in environmental responsibility and technological innovation. A key highlight of the project is the inclusion of electric-powered machinery to reduce emissions and noise pollution on-site. Furthermore, a fully electric battery unit that replaces traditional diesel generators and a fully electric cable drum trailer for handling large cable drums.

The Helsinki Cable Project installation began in mid-2024, with approximately 65% of the overall work completed as of late August 2025. The project is scheduled for completion in October 2026, followed by final acceptance and trial operation ending in February 2027.

For additional information about the project, please visit: https://www.fingrid.fi/en/grid/construction/power-cable-Helsinki/