Illustration of a subsea substation with wires connected to it and an inset highlighting a wet-mate connector.

Subsea connectors for large-scale floating wind farms

Floating wind in deep waters offers a huge energy production potential but is still at an early stage of development. For far-from-shore floating wind farms, the transmission costs including inter-array cabling account for almost half of the total costs. Improved and innovative power components are therefore key to reduce the levelized cost of energy (LCOE) of floating wind.

At deep waters, a conventional substation on a bottom-fixed structure starts to become impractical. Floating foundations are competitive with the bottom-fixed foundations at water depths of about 50 m and more feasible than bottom-fixed solutions at waters deeper than 60 m based on the future cost prognosis performed by Multiconsult in an optimistic scenario. The alternative is to have a floating substation, or to use subsea technology. By locating the substation at the seabed, the costs are reduced, and the robustness is increased compared to floating substations. Existing subsea technology from the offshore oil and gas sector can be adapted to floating wind applications, on the condition that the costs are reduced, and the capabilities are extended.

Subsea connectors are the key technology needed to enable subsea substations and must be developed to a higher voltage level than what exists on the world market today. Laboratory testing of subsea connector models during load variations have been performed in NorthWind’s WP3, in collaboration with the LowEmission Centre. The main purpose was to examine the effect of increased interfacial pressure levels and insulating liquid types on the partial discharge inception of a silicone rubber slip-on type cable termination and to study whether higher voltage ratings can be achieved by introducing additional radial pressure around the termination without changing the design and dimension of the components.

The current TRL of this innovation is 3. The development will continue in the spin-off project KSP SeaConnect (High voltage subsea connections for resilient renewable offshore grids), where Equinor, TotalEnergies and NKT are among the partners.