Turbines of the year: Offshore turbines

WORLDWIDE: Growing choice for offshore developers as new products are launched in the 6-8MW range.

Siemens SWT-7.0-154… Generates around 10% more energy than 6MW machine at windiest sites


GOLD Siemens SWT-7.0-154

In 2011 Siemens commissioned a direct-drive 6MW turbine prototype with a rotor diameter of 120 metres. A second prototype followed a year later, featuring a record 154-metre rotor. And in 2015, a prototype upgraded to 7MW was installed, generating about 10% more energy than the 6MW model at upper IEC class I wind speeds.

Relatively minor technical modifications include the fitting of stronger permanent magnets, optimised generator segments, and upgraded converter and transformer units.

The cylinder-shaped nacelle has a helicopter-hoisting platform integrated at its rear. Inside the nacelle, a huge cast main carrier forms the central structural element, while at the front there is a remarkably easy internal service hub access via the hollow generator shaft and single rotor bearing.

Two individual power-electronic converters are located inside the nacelle, together with a medium-voltage transport. The rear section of the nacelle is also spacious and service-friendly. Despite the incorporation of converters and transformer in the nacelle, it has a favourable head mass of 360 tonnes.

Both the 6MW and 7MW models are fitted with in-house developed 75-metre blades. Large-scale manufacturing facilities for the nacelles and hubs are being built in Cuxhaven, Germany, and for the B75 blades in Hull, UK.

SILVER MHI Vestas V164-8.0MW

The most powerful wind turbine in serial production today, and a clever mix of state-of-the-art innovation with the tried and tested, the V164 makes a compelling business case.

The tube-shaped MSG-PMG drivetrain is a self-supporting structure with the twin-bearing main shaft housing mounted directly on the cast main chassis. Flange connections largely eliminate misalignment risks, while a flexible shaft coupling promotes "pure" rotor torque transfer to the planetary gearbox and generator.

The combination of an unusual cast chassis and welded spaceframe elements makes for a favourable head mass of around 500 tonnes.

An E-module incorporated in the tower foot consists of the power inverter, MV-transformer and switchgear. The helicopter-hoisting platform features a passive cooling system without moving components.

BRONZE GE Haliade 150-6MW

The key technology talking point of the direct-drive 6MW Haliade turbine is the drivetrain, comprising a stationary hollow main shaft, a rotor hub with two bearings, and a 7.5-metre, medium-voltage, air-and-water-cooled inner rotor PMG.

A clever lifetime-enhancing design feature is the generator rotor part with its own separate bearing, connected to the hub via six flexible elements.

The "pure torque" principle is aimed at offering full separation of rotor-bending moments led directly into the support structure, and "pure" rotor torque is fed into the generator without constraining the air gap dimension. The power electronics are located in the tower foot for head mass optimisation.

Designed by the French firm Alstom, the wind business of which has now been incorporated into GE, the Haliade has been specified for most of France's offshore development, although its first commercial application will be the Block Island project in the US.