Solving the grid bottleneck challenge at fjord long crossings in Norwegian power transmission

Overcoming the grid bottleneck at fjord crossings in power transmission

In Norway, fjords have always been a challenging natural barrier to cross when transmititing hydro-electricity accross the country. Compared to the remaining part of the transmission lines, the conductors historically used to cross fjords are under-designed, in order to withstand mechanical loads especially in the case of long crossings.

In 2023, Statnett found in Nexans the right partner to remove this bottleneck and unleash the full capacity of power lines. To do so, Nexans OHL team designed and successfully supplied a new generation of long crossing conductors with high current carrying capacity. 

The challenge not only consisted in engineering the conductor to be installed at a fjord with over 3km of distance between banks. It was also to manufacturing, delivering and installing it as a single length, supplied on a reel of around 22 tons! 

Nexans solution

Nexans OHL team designed and supplied a 1399/366 ZTACSR high temperature low sag conductor. This single-bundle conductor - able to transmit up to 4000Amps at 420kV - is installed across a fjord with a distance between the banks of more than 3 kilometers.

Tailor-made to withstand the ice loads of the region, the conductor features a 5MS8A steel strand. Its breaking load exceeds 88 tons - over the weight of 2 trailer-trucks fully loaded! The design also includes external layers of trap-shaped wires to reduce drag.

The conductor was initially installed in 2023, and a second installation is on track for 2026.

Main features:

• Conductor diameter: 50 mm
• Linear weight: 6.8 kg/m
• Breaking Load: >88 mtons
• Design Ampacity: 3700A at 175°C
• Maximum continous operating temperature: 210°C by design
• Line Voltage: 420kV

*ZTACSR: Thermal Aluminium Conductor Steel Reinforced with trapezoidal wires for reduced drag