Design and development of megawatt wind turbines - Wind Power Generation and Wind Turbine Design - page 225

hub technology at 10 MW is suggested to be about 75 tonnes (and even lower
if possible).
Figure 23 shows the mass for the complete rotor that includes the hub, pitch
system and blades. This complete rotor mass must be carried by the main shaft
and bearings that undergoes a wide range of torque and moment loadings. The
10-turbine analysis trend suggests a rotor mass of 300 tonnes or more for a 10
MW rated machine.
The mix of design technologies for the industry study set projects that for an
improvement in technology similar to the industry thus far; one should be able to
achieve a rotor hub with a total mass of 250 tonnes for a 10 MW turbine. A stretch
target of 150 tonnes is believed possible for improved advances in rotor hub, pitch
slew bearing and blade structural design.
With respect to attaching a hub to a main shaft, an alternative technology fea-
tures the rotor hub confi gured directly with bearings and mounted on a fi xed
axle, also known as an axle pin. This arrangement is particularly attractive for a
DD machine and is similar to the steering axle (i.e. front) wheel construction
used in motor vehicles. For this later example, the wheel is analogous to the WT
rotor blade assembly and the brake rotor disk would correspond to the DD
generator − both connected together and rotating about a fi xed axle.

4.4.4 Rotor main shaft and bearings
The main shaft is one of the primary components of the WT drivetrain system. Its
main purpose is to transfer torque from the rotor hub through to the gearbox. The
main shaft and bearings must also handle loads for the specifi ed WT design IEC
TC for a period of 20 years or more. Together with thrust, wind turbulence and

Figure 23 : Rotor mass − 10-turbine analysis compared to industry study set.