Offshore Windfarm Lillgrund, Sweden

Siemens Power Generation is constructing Sweden's largest offshore wind farm in Lillgrund, off Sweden's south coast. The 110MW installation is expected to generate about 330GW/h per year, enough to power about 60,000 homes.

It will use 48 SWT-2.3-93 turbines, a variable speed version of Siemens' standard SWT-2.3-82, with a larger rotor and better economy at sites with moderate wind speeds.

The Lillgrund project is in Öresund, near Malmö, and will cost around Skr1.8bn (€18m). It will be operated by the utility company Vattenfall, with commercial operation scheduled for autumn 2007.

THREE-BLADE CANTILEVERED WIND TURBINES

The SWT-2.3-93 rotor has a three-blade cantilevered construction, mounted upwind of the tower. The power output is controlled by pitch regulation. The blades are made of fiberglass reinforced epoxy and are manufactured by Siemens in a single operation, using its IntegralBlade process. There are no glue joints between spars and shells, no weak points and no easy access for water or lightning.

The blades are mounted on pitch bearings and can be feathered 80 degrees for shutdown. Each blade has its own independent fail-safe pitching mechanism capable of feathering the blade under any operating condition, and allowing fine-tuning to maximize power output.

The gearbox is a custom-built three-stage planetary-helical design, mounted on the nacelle with flexible rubber bushings. The gearbox is fitted with a fail-safe mechanical brake at the high-speed shaft.

The generator rotor construction and stator windings have high efficiency at partial loads. The generator is fitted with a separate thermostat-controlled ventilation arrangement, and by ensuring efficient cooling can be operated at temperatures well below the normal level of the standard insulation class for long winding insulation lifetime.

The SWT-2.3-93 turbine is mounted on a tapered tubular steel tower. The tower has internal ascent and direct access to the yaw system and nacelle. The turbine controller is a microprocessor-based industrial controller; similar to the type used in other Siemens wind turbines.

The controller is complete with switchgear and protection devices. It is self-diagnosing and has a keyboard and display for easy readout of status and for adjustment of settings.

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

The turbine safety system has several redundant levels, including an independent pitch system for each of the blades. As a result the turbine can shut down safely from any operating condition. The WebWPS SCADA system offers long-distance control and a variety of status views and useful reports from a standard internet web browser. The SWT-2.3-93 turbine uses the NetConverter system with ride-through capability for all normal faults.

SEVERAL OFFSHORE SCANDINAVIAN PARKS

In 1991, Siemens installed the first offshore wind farm in Vindeby, Denmark. It also erected the world's current largest, the 165MW Nysted offshore wind farm in the Baltic Sea, in 2003. Siemens has also recently signed an offshore contract for 25 of its 3.6MW wind turbines for the Burbo Banks offshore wind farm in Liverpool Bay off the British west coast, scheduled for commissioning in autumn 2007.

In 2008, Siemens will start building the world's largest offshore wind farm off the east coast of Great Britain. The Lynn and Inner Dowsing project will have 54 SWT-3.6-107 wind turbines, with a maximum capacity of 180MW. It will be operated by British gas provider Centrica.

ABB WINS $16M POWER CABLE CONTRACT

ABB has won a contract worth $16m (about €12m) from Siemens to supply over 33km of power cables for Lillgrund. Reliable XLPE cable interconnections carry offshore wind power to the mainland.

The single core AC cable and armored three core AC cable has integrated optical fiber, and is supplied by ABB's high voltage cable and accessories production facilities in Sweden. Project scope includes underground and submarine XLPE (cross-linked polyethylene) insulated cables, cable laying and cable installation.

ABB will supply and install six-kilometer-long, 145kV underground cables, and 27km-long 145kV and 36kV submarine cables to interconnect the turbines and transmit the power to the Swedish mainland.

Bladt Industries A/S is delivering the offshore transformer platform.