New 400 kV Tuna substation construction – a key energy Link for Sweden

Sweden continues to strengthen its energy infrastructure through the reconstruction and modernization of key power facilities. The construction and reconstruction of the 400/220 kV Tuna substation, which connects the Stockholm and Uppsala regions with the Forsmark nuclear power plant, represents a major technological and engineering undertaking.

Reconstruction of the Tuna substation and its integration with the 400 kV transmission line will enable an additional 320 MW of transmission capacity, further enhancing the stability of Sweden’s power grid. In addition, this substation becomes a critical hub for the efficient distribution of electricity produced at the Forsmark nuclear power plant toward Sweden’s urban and industrial centres.

• Substation voltage level: 400/220 kV
• Increased supply capacity: 320 MW
• Number of new 400 kV bays: 3
• Number of new 220 kV bays: 1
• Modernization of protection and control systems

The reconstruction includes capacity expansion, assembly of advanced protection systems, and optimization of infrastructure for more efficient and secure power transmission.

• Work on connections linked to the Forsmark nuclear power plant, requiring strict safety protocols and precisely scheduled outages
• Reconstruction while the substation remains in operation, necessitating a phased approach to ensure uninterrupted supply
• Integration with the existing network, including connection to current transmission lines and expansion of transmission capacity
• Strategic relocation of the 220 kV system and integration of the 400 kV line into the substation to optimise space and improve operational efficiency

Elnos Group is responsible for the following key tasks:

• Complete electrical assembly works on three new 400 kV bays
• Replacement of secondary equipment in existing 400 kV bays
• Construction of a new 220 kV bay and replacement of secondary equipment in one existing 220 kV bay
• Assembly and connection of secondary equipment in one old and one new 220 kV bay of the substation
• Secondary and primary connections for the new power transformer
• Replacement of secondary equipment on the existing power transformer
• Connection of high-voltage primary circuits within the substation
  

Assembly of general electrical systems in the new control building

• Increased power transmission capacity within Sweden
• Enhanced energy security for the Stockholm and Uppsala regions
• Direct integration with the Forsmark nuclear power plant, improving reliability and efficiency of energy transmission
• Modernization of national power infrastructure through advanced protection and control technologies
• Long-term reduction of network losses, contributing to more efficient distribution of electricity

The construction and reconstruction of the Tuna substation is a key step in strengthening Sweden’s power grid, enabling more stable and efficient utilization of nuclear energy. This project further reinforces Elnos Group’s position as a leading contractor in power infrastructure projects across Europe.