Turbines

The wind turbines selected for the site are Siemens 3.6MW - the latest model in the company’s product range. The rotor is a three-blade cantilevered construction, mounted upwind of the tower while the 52m blades are made of fiberglass-reinforced epoxy resin and manufactured in a single operation representing state-of-the-art technology. The turbine is mounted on an 80m-high tapered tubular steel tower with an internal ascent.

 

The turbine operates automatically, self-starting when the wind reaches an average speed of 3–5 m/s. The output increases with the wind speed until it reaches 13–14 m/s. At that point, the power is regulated at rated power. If the average wind speed exceeds the operational limit of 25 m/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, are being 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. Once completed, the monopiles will be transported to Kats, Vlissingen, Netherlands for storage before installation. 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 50 and 55 metres long, with a 5m diameter and weighing from 400 to 600 tonnes.

Contractor MT Højgaard will use the “Svanen”, its purpose made self-powered heavy-duty floating crane, to drive foundation piles 32-36 metres 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 contact by AREVA T&D UK.

 

A collaborative approach to the design of the offshore substations has resulted in a concept, which should be safer, more accessible for maintenance and better structurally than conventional offshore substationsThe key concept is the decentralisation of the transformers, which should not only decrease the likelihood of one transformer affecting the others in the event of an incident, but also improve access for safety and evacuation needs.

 

Each of the Sheringham Shoal substations will be 30.5 metres long, 17.7 metres and wide and 16 metres high. They are scheduled to sail out from Hartlepool in September 2010 with installation at the wind farm due for 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 will weigh 27 kilograms per metre and will run to 26 kilometres while type two will be lighter, at 18 kilograms per metre, but a much longer 56 kilometres.