From the outside, modern wind turbines look rather similar to each other. Inside the nacelle, wind turbines vary considerably in terms of the type of powertrain used. The arrangement of the components in the nacelle is subject to different design principles: four-point suspension, three-point suspension, compact rotor gearbox unit, direct drive.
Four-point suspension (also known as double rotor suspension or separated design) is characterized by a main shaft bearing consisting of one slew bearing or two separate bearings. Weight forces as well as yawing and nodding moments from the rotor are completely transmitted to the main frame. Four-point suspension is mainly used in large multi-megawatt turbines.
The main advantage of this arrangement is that neither weight forces nor yawing and nodding moments from the rotor are transferred to the gearbox. Furthermore, gearbox replacement is comparatively simple.
The main disadvantage of this design is its overdetermination, which leads to constraint forces in the gearbox.
In addition to these gearbox supports, ESM supplies a wide range of products precisely adapted to this type of drivetrain. As well as generator mounts, cover mounts, decoupling elements are used for pitch control, and couplings. Noise and other unwanted vibrations (e.g. tower oscillations) can be reduced with ESM tuned mass dampers.
The three-point-suspension (also known as partially integrated suspension) is the most common suspension. In this case the drive train along with the rotor are supported by the rotor shaft bearing and two additional points of the gearbox on the main frame.
The advantages are the comparatively simple design and the static determination. The gearbox has to be able to absorb the loads from the rotor weight and the resulting yawing and nodding moments. Gearbox replacement is somewhat involved because the rotor has to be supported.
Rubber bushings are usually used for gearbox support. ESM has developed a wide range of clamping bushings which isolate structure-borne noise and feature a simple, easy-to-fit design for a long service life.
In addition to gearbox mounts, ESM provides a wide range of products precisely adapted to this type of drivetrain. Apart from generator mounts, cover mounts as well as decoupling components for both pitch control and the main bearing are used. Noise and other unwanted vibrations can be reduced with ESM tuned mass dampers.
Compact rotor gearbox unit
The compact rotor gearbox unit (also known as an integrated design) is the traditional design used for the drivetrain. As the name implies, the rotor forms a compact unit with the gearbox. There are no free shafts, bearings or couplings.
This unit is elastically connected to the main frame to isolate structure-borne noise. The decoupling component must be able to transmit all the forces and moments occurring to the main frame. ESM offers various mounting systems for this purpose. Depending on the output and thus the size of the gearbox, they are fitted beneath or around it.
In addition, ESM offers a wide range of products precisely adapted to this type of drivetrain. As well as generator mounts, cover mounts and decoupling components are used for pitch control. Noise and other unwanted vibrations (e.g. tower oscillations) can be reduced with ESM tuned mass dampers.
In wind turbines with direct drive (also known as gearless), the rotor output is transmitted straight to the generator. Therefore, there is no gearbox between the rotor and the generator. Instead, multi-pole synchronous generators are directly connected to the rotor hub, meaning the drivetrain can be kept very short.
To disconnect the hub from the rotor and the generator, ESM has developed an elastomeric hydraulic coupling. This allows high torque to be transmitted while compensating for the radial offset of the hub and the rotor-generator unit.
In addition to couplings, cover mounts and decoupling components are used for pitch control. Audible sounds and the vibration amplitudes of the first and second natural frequency of the tower can be significantly reduced with ESM tuned mass dampers.