Longest underground high-voltage cable connection in the Netherlands ready for use

The onshore connection for Fryslân wind farm is ready for use. The 55-kilometre cable route to the Oudehaske high-voltage substation near Heerenveen is the longest underground high-voltage cable connection in the Netherlands. The first electricity is expected to be fed into the grid this spring.

The 110 kV cable route runs from the wind farm’s new substation at Breezanddijk along the A7 highway to grid operator TenneT’s high-voltage station at Oudehaske. The Zuiderzeewind contractor consortium ( Van Oord and Siemens Gamesa Renewable Energy) was responsible on behalf of Windpark Fryslân for the first 23 kilometres of the connection: from the substation to Bolsward, while TenneT was responsible for the remaining 32 kilometres between Bolsward and Oudehaske.

Both parties selected Visser & Smit Hanab to build the cable connection. The activities for the first section started in 2019. A total of 196 kilometers of power cables, provided by Prysmian, were buried for TenneT and another 150 kilometers for Windpark Fryslân. The cable connection runs parallel to the A7 motorway. 60% of it was constructed in open excavation, the rest was drilled under waterways and motorways.

Because the route runs mainly along a narrow roadside strip, the cables had to partly be placed above each other. In order to properly dissipate the heat released by the high-voltage cables and to prevent drying out and overheating, all cables are laid in a layer of loamy sand. This first section was already completed in the summer of 2020.

Temporary welding solution at Bolsward

The two cable sections were finally welded together at Bolsward and successfully tested. The weld between the high-voltage cables is a temporary application. TenneT is preparing for a new high-voltage substation to the west of the De Marne industrial estate near Bolsward as part of a grid reinforcement in Western Frisia. By connecting existing and new cable connections, this will create an extra ‘ring’ in the West Frisian high-voltage grid from 2023, which will not only increase the capacity, but also the reliability of the electricity grid.


In summer and autumn 2020, TenneT and Windpark Fryslân and partners sown various strips of soil above the cable connection along the A7 (except for the part on the Afsluitdijk) with indigenous flower species: A “flowerline” on the “powerline”.

The almost 383 MW wind farm is due to be completed this summer. All foundations are in place while inter-array cable installation is ongoing. Zuiderzeewind also recently started with the installation of the first of 89 Siemens Gamesa Renewable Energy turbines (type SWT-DD-130, 4.3 MW).

Input your search keywords and press Enter.