Turbines of the year: Offshore turbines

WORLDWIDE: The super-sized new generation machinery that is driving down offshore wind costs

Siemens SWT-7.0-154… Started life as a 6MW unit, and will be upgraded to 8MW+


GOLD Siemens SWT-7.0-154

The 7MW SWT-7.0-154 (or D7) enjoys huge market demand, supported by an advanced mature supply chain already (partly) in operation.

Large-scale manufacturing facilities for B75 blades were completed in Hull, UK, while assembly of nacelles and hubs will start in Cuxhaven, Germany, next year.

Siemens has also developed innovative solutions aimed at driving down LCOE, such as its newly introduced roll on-roll off vessels for transporting nacelles, towers and blades to various supply ports.  

The direct-drive D7 (prototype 2015) is an evolution of the 6MW D6. During 2011 Siemens commissioned a 6MW prototype with 120-metre rotor diameter, followed by a second prototype with enlarged 154-metre rotor diameter in 2012.

The step-by-step upgraded SWT-7.0-154 with unchanged rotor size generates about 10% more energy compared with the SWT-6.0-154 (D6) predecessor, but at upper IEC class I sites.

The technical modifications include stronger permanent magnets in the outer-rotor generator, and upgraded converter and transformer units for matching the increased power rating.  

Inside the cylindrical-shape nacelle a huge cast main carrier forms the central structural element, while easy internal service hub access is provided via the hollow generator shaft and single rotor bearing.

Two individual power-electronic converters are located inside the nacelle, together with a medium-voltage transformer. The D7 retained a favourable head mass of around 360 tonnes. An 8MW-plus SWT-8.0-154 (D8) has been announced

SILVER MHI Vestas V164-8.0MW

Currently the most powerful turbine with the largest rotor, the V164 combines proven and innovative solutions. New is a power mode option up to 8.4MW. The turbine enjoys strong market demand, and the first offshore project with 32 units has been completed.

The tube-shape medium-speed drivetrain is a self-supporting structure with the main shaft housing incorporating main shaft and two bearings mounted directly on a cast main chassis.

Flange connections between main drive components virtually eliminate misalignment risks, while a flexible shaft coupling promotes "pure" rotor torque transfer to the gearbox and generator.

The clever structural design contributes to a favourable head mass. Power inverter, MV-transformer and switchgear are all located in the tower base.

BRONZE GE Haliade 150-6MW

The 6MW direct-drive Haliade 150-6MW features an unusual drivetrain design comprising a stationary hollow main shaft (pin), a rotor hub with two bearings and a 7.5-metre medium-voltage air-water cooled inner-rotor PMG.

A lifetime enhancing design feature is that the generator rotor part has separate bearing, and is connected to the hub via flexible elements.

This principle aims at offering full separation of rotor-bending moments fed directly into the support structure, and "pure" rotor torque fed into the generator without constraining the air gap dimensioning during operation.

A head-mass optimising measure was to locate all power electronics in the tower foot. Rumours suggesting a capacity upgrade to 7MW with unchanged rotor size have not been confirmed officially.