The Sabella D10 tidal turbine, submerged in the Fromveur passage south of Ushant Island1 at a depth of 55 meters, was connected to its submarine electrical cable in the morning of September 21 by BOURBON, by the Argonaute. The turbine can now supply electricity to the island. For the record, the submarine electrical cable was installed in late May 2015 by BOURBON, by the same vessel.
In late July, a first connection operation was initiated with BOURBON and the Argonaute but was unsuccessful, due to bad weather conditions. Offshore operations in this area of strong currents can only take place with the combination of weak currents – corresponding to low tidal coefficients – and favorable weather conditions, especially in terms of wind and swell.
Therefore, a new operation was scheduled. First off, during the night of Sunday the 20th to Monday the 21st, the objective was to align the two cables so that their ends would be facing one another, and install a launching arch to respect the cable curvature radius of the installation loop.
At the end of these two cables are two half-connectors, like giant plugs, weighing 200 kg each. These cables include, in addition to the electrical power lines used to export the electricity, fiber optics to control and monitor the machine and auxiliary cables that power the tidal turbine equipment.
Connection of the two half-connectors: a first!
During the second phase during the slack tide on Monday morning, the two half-connectors were raised again then opened. The fiber optic and power cables in the two cables were then connected individually. The two half-connectors were then brought together in order to make the power connection. The connectors were then closed again so as to form a single piece, and thus create a seal. Lastly the two connected cables were laid on the seabed.
Interventions in these areas of strong currents are considered marine pioneering, even for experienced players in offshore work. This operation was made possible by the close collaboration between the SABELLA and BOURBON engineering teams, as well as the experience and the operational control of the BOURBON crews.
Begining of the electricity production phase
Once the connection was made, the first communication tests with the tidal turbine were performed successfully from Ushant. The brakes on the tidal turbine could then be loosened to allow the rotor to perform its first rotations with the Fromveur current, and the tidal turbine was able to produce and export its first kilowatt hours to land...
In the coming days, the tidal turbine will be connected to the Ushant electricity grid. The Sabella D10 will then be the first tidal turbine connected to the French electricity grid.
1Brittany, Western France.