Turbines

The wind turbines selected for the site are Siemens 3.6MW. The rotor is a three-blade cantilevered construction, mounted upwind of the tower while the 52m (170 feet) blades are made of fibreglass-reinforced epoxy resin and manufactured in a single operation representing state-of- the-art technology. The turbine is mounted on an 80m (262 feet) high tapered tubular steel tower with an internal ascent.

 

The turbine operates automatically, self-starting when the wind reaches an average speed of 3-5m/s. The output increases with the wind speed until it reaches 13-14m/s. At that point, the power is regulated at rated power. If the average wind speed exceeds the operational limit of 25m/s, the turbine stops. When the wind drops back below the restart speed, the safety systems reset automatically.

 

Foundations

These 90 giant monopile structures, as well as the transition pieces which join the turbines to them, will be fabricated by tubular structure specialist, the Sif Group, at their plant in Roermond, the Netherlands, on a sub-contract to the main foundation contractor, MT Højgaard. The transition pieces will be transported to Belgium and the Hoboeken plant of offshore foundation pioneer, Smulders, for outfitting.

 

Each foundation is made to individual specifications and will be between 44 and 61 metres long, with a 4.2-5.2m diameter and weighing from 375 to 530 tonnes.

 

Contractor MT Højgaard will use the “Svanen”, the self-powered heavy-duty floating crane, to drive foundation piles 23-37m (75-121 feet) into the seabed and mount the yellow-painted transition pieces on top, in preparation for the installation of the two substations and 88 wind turbines in 2011.

 

Offshore substations

The wind farm will include two 1000 tonne offshore substations. Offshore construction specialist Heerema will fabricate and load out two substation platform topsides from its yard in Hartlepool, County Durham, following the award of a contract by AREVA T&D UK.

 

Each of the Sheringham Shoal substations will be 30.5 metres long, 17.7 metres wide and 16 metres high. They are scheduled to be installed at the wind farm early 2011.

 

Cables

The offshore cables are being produced by global cable experts, Nexans in Norway at their manufacturing plant in Halden, south of Oslo, while the fibre optical elements are being produced in Rognan, in the northern part of Norway. The power and optical cables will be bundled together into one unit.

 

There will be two long export cables carrying the power from the wind farm to landfall - one 23 kilometres and one 21 kilometres in length, with a weight of 77 kilograms per metre. That’s a total weight of 3,388 tonnes!

 

There will be two different types of infield cables connecting the turbines and the offshore substations. Type one (27kg/m) has a total length of 26 kilometres and will be used to connect the turbines closest to the substations, while type two (18kg/m) has a total length of 56 kilometres and will connect the turbines further out. Both cable types will be cut into actual lengths during installation.