Connectors are pluggable connections between two segments of cable or between the cable and a floating substructure.

Joints are fixed connections between two segments of cable.

What it costs

About £5.8 million for a 450 MW floating offshore wind farm.

Who supplies them

First Subsea, MacArtney, Pfisterer, Power CSL, SBT Energy and Subsea Energy Solutions. Factory joints are installed in-house by cable manufacturers during the manufacturing process.

From left to right: Wet mate connector and dry mate connector.
Dry mate connector and wet mate connector. Images courtesy of MacArtney. All rights reserved.

Key facts

Connectors allow cables to be disconnected and reconnected and can either sit on the sea bed or on the floating substructure.

They can be either dry mate or wet mate. Dry mate connectors are a mature and proven technology, but the connection must take place out of the water, usually on board a vessel or the floating substructure. Wet mate connectors can be disconnected and reconnected underwater but are not currently available at 66 kV and are a current area of research.

Not all floating offshore wind farms require connectors, and this is largely depend on the maintenance strategy of the developer. Disconnection of the floating substructure and the dynamic cabling system is required for a tow-to-port maintenance strategy meaning that connectors could be beneficial. Once 66 kV wet mate connectors have been developed and proven for array cables, they are likely to be used at each turbine for projects using a tow-to-port maintenance strategy. An in-situ maintenance strategy allows the turbine-floating substructure assembly to remain in place and so connectors may not be required.

Floating substructure designs that pivot downwind of a turret will require a rotating connector.

Cable joints typically sit on the sea bed. There are two types:

  • A factory flexible joint connects individual segments of cable core into one continuous length during the lay-up process. Crucially, the joint must have the same electrical, mechanical, and thermal properties as the rest of the cable and result in a joint that does not hamper installation or increase the risk of cable failure.
  • A field rigid joint is a manufactured product. It may be supplied to the wind farm owner or the offshore transmission owner (OFTO) with the cable in case of failure during operation or supplied as a planned joint to link sections of cable. In floating offshore wind farms field rigid joints could be used to connect dynamic and static array cable sections, or to connect dynamic and static export cable sections if a floating offshore substation is used.

Field rigid joints have generally been bespoke products because of the substantial variations in cable design between wind farms. There is growing interest, particularly by OFTOs, in developing joints that are suitable for a range of cable designs.

What’s in it

Guide to a Floating Offshore Wind Farm