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. 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 Seaway Heavy Lifting will use the state of the art crane vessel the Oleg Strashnov to drive foundation piles 23-37m (75-121 feet) into the seabed and mount the yellow-painted transition pieces on top, to support the installation of the two substations and 88 wind turbines.

 

Offshore substations

The wind farm includes two 1000 tonne offshore substations. Each of the Sheringham Shoal substations is 30.5 metres long, 17.7 metres wide and 16 metres high. Offshore construction specialist Heerema fabricated the offshore substations at their yard in Hartlepool in North East England. The complex logistics operation to transport them to the Sheringham Shoal site started in November 2010 when they were transferred from the fabrication hall to an outside location. The operation to get the substations out of Victoria quay and on to Dina Launcher, the barge which brought the substation to site, required careful planning and precise manoeuvring.

 

The substations were lifted onto their individual foundations by the state-of-the-art crane vessel Oleg Strashnov. The first substation was installed at its location at 23:32 on 8 May 2011, and the second substation was lifted onto its foundation at 14:20 two days later.

 

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 are 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.