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NSK in the Wind Industry
Wind turbines generate electricity in adverse, constantly changing conditions both onshore and offshore. This places extremely high demands on all of the turbine’s components – especially the bearings. As well as enduring high speeds, they have to withstand dynamic loads. This means you need a partner with experience in this sector and a precise knowledge of bearings. We have been serving the wind energy industry for over 15 years, making us the perfect choice.
NSK bearings have gained a global reputation for outstanding quality built on their long life, reliability, resistance and carefully considered design.
To ensure that we can develop the perfect solution for you, we have set up a Wind Energy Team combining our sales and application engineering expertise. The latest research results from our technology centres are also incorporated into this knowledge pool. Our facilities are capable of testing large and giant bearings for wind turbine rotor shafts in a range of conditions.
Whatever you need, our Wind Energy Team is happy to support you with advice, new-development services and maintenance.
Operating conditions: high radial and axial loads
The dynamic wind loads acting on the rotor place a high level of mechanical stress on the power train components of a wind turbine. The main bearing system has to absorb both radial loads and axial forces, including the rotor shaft’s bending moments. In integrated drive trains, the rotor hub is connected directly to the generator or the gearbox. Double-row taper roller bearings are generally used in this area.
Today’s rotor shafts feature various bearing arrangements. One popular concept uses two individual rotor shaft bearings. So-called four-point support that can either be realised as a classic locating/non-locating bearing system or using a floating set-up.
With the three-point support, the rotor shaft just has one main bearing. The connected gearbox is used as the second bearing.
NSK’s spherical roller bearings and taper roller bearings are the ideal solution for both individual rotor shaft bearings and integrated bearing arrangements as they boast a high degree of bearing stiffness.
NSK High Performance Standard (NSKHPS™) spherical roller bearings are particularly well suited to this application with their increased load ratings and extended permissible speed range.
NSKHPS™spherical roller bearings
Spherical roller bearings - CAM cage
Operating conditions: variable loads
A wind turbine’s main gearbox serves to convert low rotor speed into high generator speed. The gearboxes commonly used in megawatt-class turbines consist of at least one planetary stage and one or two spur-gear stages. Operating conditions for wind turbines make high demands of the bearings used for the individual shafts and gearbox components.
Bearings in the fast part of the gearbox are subject to frequently changing wind speeds, which leads to high accelerations and speeds changes. By contrast, the bearings in the input stage are subject to very high static loads during calm weather or strong winds (turbine shut down).
Another factor is the weight of the gearbox, which must be minimised as the unit is mounted at a height of up to 120 m. The bearings must be designed accordingly.
When we design bearings for a main gearbox, we comply with international standards and have our work checked by official institutes. Each bearing is designed for a calculated life of at least 20 years. This is only possible if data on the operating and ambient conditions is incorporated into the calculations as precisely as possible.
The STIFF software developed by NSK enables all operating specifics (loads, bearing design, ambient design, material properties, temperatures, lubrication, etc.) to be taken into account.
HR taper roller bearings and cylindrical roller bearings from NSK are ideal for main gearboxes as they remain reliable despite changing loads and also have high load ratings. They can be arranged in various different constellations – as locating/non-locating bearings, adjusted bearing arrangements or floating bearings.
Operating conditions: sudden charge exchange caused by circulating currents
The role of a generator in a wind turbine is to convert mechanical energy into electrical energy. Factors such as magnetic asymmetry or the use of frequency converters often generate circulating currents which are dissipated in the space between the rotor and the stator. These currents travel via the bearings. The frequent and sudden charge exchange via the very thin lubricant film can cause damage to the raceway and the rolling elements (formation of microcraters). Electrical corrosion occurs if the bearing is subject to these discharges for a sustained length of time.
Conventional deep-groove ball bearings cannot withstand the mechanical loads in generators. However, ceramically coated deep-groove ball bearings and hybrid bearings from NSK are ideal, as they are not susceptible to electrical corrosion.
These coated deep-groove ball bearings have an insulating ceramic layer which electrically separates the bearing from the casing (stator). Although this layer is just a few tenths of a millimetre thick, it has a dielectric breakdown strength of several thousand volts.
With their ceramic rolling elements, hybrid bearings also serve to electrically isolate the stator and the rotor.
Ceramic-coated ball bearings
Operating conditions: high degree of static load
Yaw gears turn the nacelle into or out of the wind. They serve to position the equipment pod so that the whole rotor area is vertical to the wind. Pitch gears are needed to adjust the rotor blades to make maximum use of the kinetic energy.
Once the rotor blades or nacelle have been angled, the drives often stay in this position for several hours. During this time, the drives have to withstand constant load changes and vibrations.
Total Quality Solution:
HR taper roller bearings , EM Series & EW Series of cylindrical roller bearings with high static load ratings
NSK offers a wide range of taper and cylindrical roller bearings with high static load ratings which can be used to realise drives for any rated output.
NSKHPS™ Spherical Roller Bearings