Construction
Barrow Offshore Wind Farm construction
Construction and commissioning work for Barrow Offshore Wind Farm was completed in June 2006, a little over a year after offshore work got underway in the East Irish Sea.
The start of offshore preparation work was marked by the arrival of the offshore substation topside platform to Barrow port at the end of April 2005. Local company Agrilek won the contract to fit-out the offshore substation with electrical components, providing work for a 20-strong team.
The 480 tonne substation was installed using a specialist vessel called the Matador 3. Stafford-based firm Areva were responsible for the substation electrical design. It transforms the 33kV power generated from the wind turbines up to 132kV, which is then exported to the national grid connection point at Heysham on the Lancashire coast through a 27km long subsea transmission cable. Installation of the subsea export cable was carried out by a vessel called the Pontramaris.
Offshore work to install monopiles, the cylindrical steel foundations which provide a base for the turbine towers was completed in November 2005. The work was undertaken by Middlesbrough-based firm Marine Projects International (MPI) using a turbine installation vessel called the Resolution.
This 38m-wide ship also installed the turbine towers, nacelles and blades, and by March 2006 it was possible to generate clean electricity from the first row of turbines.
Offshore construction process
The monopile is a cylindrical steel foundation, which provides a firm base for the turbine. These were driven or 'piled' to varying depths depending on seabed conditions, using a large hydraulic hammer. Geotechnical survey work was carried out in advance to determine the nature of the seabed and in some cases, due to the geology, some drilling was used to allow the monopile to reach the desired design depth.
A transition piece was then lifted into position, slid over the monopile and secured with a cement adhesive. The transition piece includes a boat landing arrangement, ladders and a platform to allow future maintenance access to the turbine.
Cable laying within the wind farm was carried out before the turbine installation. The cable which has been laid to transmit power to shore from the offshore substation consists of copper conductors as well as a number of fibre optics for communication and control purposes.
The 75 metre tall towers were installed by bolting them onto the transition pieces. The Barrow turbine towers consist of a lower, an intermediate and an upper section. The towers were pre-fitted onshore with ladders, personnel lifts, power cables, switchgear, lights and other essential equipment.
The remainder of the turbine assembly consists of a nacelle (the housing at the top of the tower that contains the generator, gearbox and transformer) hub and blades. To minimise offshore lifts, the nacelle, hub and two of the three blades were assembled onshore in what is referred to as a "bunny ear" configuration and transported by the Resolution to site.
This was lifted into place as a single assembly and the final lift was the third blade, which was bolted into the hub.
Onshore work to enable power to be exported from the wind farm to the national grid included cabling and the building of a new substation at Heysham.
