Electrical substation:

Central element of the offshore wind farm

Installed since July 8, 2022, the electrical substation plays a key role in the operation of the offshore wind farm in the Bay of Saint-Brieuc. Intended to transmit the electrical flows between the wind turbines and the Earth, its installation is a particularly important step in the progress of the project.

Zoom in on its characteristics.

Features and assembly

The electrical substation was designed and manufactured by Iemants (a subsidiary of the Smulders Group, which in turn is a subsidiary of the Eiffage Group) and Equans, with medium and high voltage equipment supplied by GE Grid solutions.
A complex and massive element, the electrical substation is composed of two separately manufactured elements assembled at sea:

  • The lower part or "jacket" type foundation, which is fixed to the seabed by piles.
  • The upper part or "topside", which houses all the electrical equipment.

In terms of proportions, the foundation of the electrical substation is 63 meters high with a total weight of 1,630 tons. The upper part is 55 meters long, 31 meters wide and 23 meters high, with a total weight of approximately 3,400 tons.

On the production side, the engineering and fabrication of the jacket foundation and the steel structure of the upper part were carried out by the Equans-Iemants joint venture.

The low-voltage electrical part of the upper part was designed and equipped by Equans. It includes the auxiliary systems and the integration of the medium and high voltage equipment, which are supplied by GE Grid Solutions.

The jacket and top section were pre-assembled by Smulders in Belgium, at the Hoboken yard near Antwerp. The final assembly of the upper part was carried out at the Equans yard, also in Hoboken, Belgium. Finally, the final assembly of the jacket foundation was carried out at the Heerema yard in Vlissingen, the Netherlands.

Better understand how it works

The electrical substation collects the energy produced by the 62 wind turbines of the park, and raises the voltage from 66 kV to 225 kV through power transformers. This collected energy is then injected into the terrestrial network via a series of submarine and underground cables. On land, it is carried to the Doberie substation in the town of Hénansal (22).

To ensure a reliable electrical link between the park and the terrestrial network, the electrical substation will house all the park's automated control systems.

Connection to the electrical network 

The connection of the electrical substation to the terrestrial electrical grid is planned for 2023. The electrical substation will be commissioned by technicians from Equans and Smulder. Once operational, the fully automated electrical substation will be remotely controlled and monitored. If necessary, technicians will be assigned to carry out maintenance operations via personnel vessels.

The key stages of its installation

Loading and transport
On Saturday, June 11, 2022, the upper part and the jacket foundation of the electrical substation were successfully loaded for transport to the offshore wind farm in the Bay of Saint-Brieuc.

The first step was to load the upper part at theEquans BeLux assembly yard in Hoboken, Belgium.

At the same time, the jacket foundation of the electrical substation was safely loaded onto a pontoon from Vlissingen, the Netherlands.

The installation

The electrical substation was installed in two stages. First, the 1,630-ton "jacket" foundation was installed on its four piles. Then, the topside, weighing 3,400 tons, was installed on this foundation during the night of July 6, 2022. This two-stage maneuver was carried out by Saipem's teams, and more specifically by their semi-submersible crane ship, the Saipem 7000. This vessel is one of the largest jackups in the world and uses technology that is particularly well suited to this type of technical operation. This installation was completed during the night of July 6 to 7, 2022.

It is the first offshore electrical substation in Brittany, but also the second substation installed on a French wind farm after the one in Saint-Nazaire.

To follow the progress of the work and the next steps in the installation of the park elements