Making offshore connections
The array cables connect the wind turbines to each other and to the offshore substations. They each measure between 650m and 1,200m in length. For Phase One, we laid over 200km of array cabling using specialised vessels and ROV’s.
The export cables run from the offshore substations to the onshore substation at Cleve Hill, where the power is flowed into the national electricity network. The cables were buried in trenches dug into the seabed using the special cable installation barge and plow, ‘Stemat Spirit’. As well as transporting electricity, the export cables hold vital fibre optic wires that we use to communicate remotely with and control the wind turbines. We laid around 220km of export cabling in Phase One and each of the four cables was installed in one continuous length of over 50km.
Connecting the export cables
To connect the export cables to the onshore substation, we drilled through the seawall at Cleve Hill. We chose this option as it was the most unobtrusive method of installing the cables. Horizontal Directional Drilling (HDD) conduits were required, so we needed specialist plant and machinery on site to enable us to carry out the work. After the holes were drilled, we installed cable ducting and closed the holes until we are ready to pull each cable through. The first export cable was installed towards the end of 2011; the second cable was installed early in 2012 with the remaining two cables installed later that year.