Abstract: The present large-scale wind turbine spindle bearings to withstand load conditions, analysis of the spindle bearings partial load conditions , the impact of lubrication and clearance of carrying capacity and life , and the impact of vibration on the spindle bearing life of their own , proposed focus of the design that need attention , comments and suggestions to improve .
Keywords : Spindle bearings ; partial load ; lubrication ; clearance ; bearing vibration
Wind turbines increasing the power to bring wind turbines to increase the volume and load , which the reliability and safety of wind turbines has put forward higher requirements. Wind turbine spindle bearing is absorbed by wind loads and passing the main components of the load , and its performance has an impact not only on the transmission efficiency , but also determines the main drive chain maintenance costs . In this paper, large-scale wind turbine spindle bearing load related problems were analyzed.
A wind turbine spindle bearing load cases
Currently, the drive chain design wind turbine is absorbed by the spindle bearing most of the load from acting on the wind turbine as possible , including radial and axial force and bending moments . Most of the subsequent absorption of the gearbox and generator unfavorable load bearing spindle , the only favorable torque transfer to the high-speed side wind turbines . Therefore, the spindle bearing life raised higher requirements . Spindle bearing arrangement main drive chain to support a single point , two-point support , etc., bearing adopted different forms , but the ultimate goal is to only transfer torque to the rotating components such as gearboxes or generators . Bearing is subjected to radial forces , axial forces and bending moments of their role , therefore , for different forms of arrangement to be considered in the selection of the type of bearings and what form will have to bear the load .
Figure 1 is a time sequence diagram of the wind speed . Wind will change with time because of constantly changing load changes also will eventually repeated impact which will cause the bearing to bearing failure . Due to the instability of the wind , some wind farms with high turbulence effects , and in extreme wind speed, wind loads on wind turbine component damage ability. Therefore, increasing the carrying capacity and life of the bearing will not only improve the stability of the unit to a certain extent , and can significantly reduce maintenance costs.

Wind speed time sequence diagram in Figure 1
2 spindle bearings carrying capacity analysis
2.1 Analysis of partial load
Currently , the main spindle bearings tapered roller bearings, spherical roller bearings, cylindrical roller bearings 3 , etc., to make bearings have a longer life and greater carrying capacity, often using two or three roll bearing arrangement . In the design of roller bearings , the main consideration of the bearing clearance and modification of rollers and lubricant selection and other factors. For conventional transmission chain , the spindle and spindle bearings are often connected to long , and the wind wheel center farther away from the spindle bearings , will produce some additional moment , although rigid spindle relatively good parts , but it is possible the loads due to the deformation of the bearing inner and outer rings of different axes so that the spindle is connected , a certain angle, resulting in partial load bearing . Figure 2 is a condition, two cylindrical roller bearings Spherical roller stress distribution . Figure 2 shows , two cylindrical roller bearing load substantially symmetrical distribution , indicating that the contact stress conditions more uniform bearing components , and running well, plenty of oil in the case , no temperature rise. But in another condition ( shown in Figure 3 , a contact pressure contact with the roller carrier is small , a large stress is another column , the conditions, set out by unilateral severe , may roller bearings which resulted in a rolling , sliding case another column appeared , the lubricant film will be unevenly distributed, bearing components may be in direct contact with each other , resulting in accelerated heat bearing oil film thinning , resulting in poor lubrication of the bearing components , increased bearing wear .

Figure 2 roller bearing contact stress distribution ( all load conditions )

Figure 3 roller bearing contact stress distribution ( partial load conditions )
Spindle bearings single row appears under load is too large and the main reason is the deflection of the spindle bearings and bearing its own elastic deformation , using the long axis of the bearing arrangement is not conducive to a special bearing load evenly. Therefore , to the extent possible , the minor axis of the main drive chain is arranged to shorten the distance from the center of the bearing and rotor , and to improve the rigidity of the spindle, to reduce the flexural deformation , which helps to reduce the bending moment on the bearing attached , the bearing bearing uniform as possible , to improve bearing life.
2.2 Analysis of lubrication and bearing clearance
Bearing lubrication, temperature effects and clearance of their large carrying capacity . The lubricant may be appropriate to give the bearing member between a good lubrication , especially at low temperature , a lubricating oil having excellent viscosity-temperature characteristic , the bearing friction torque can be reduced when starting , and a lubricating oil of a certain anti- diluted with water performance. In order to prevent the lubricant film is damaged, avoid direct contact between the parts appear dry friction condition, bearing temperature expansion , reduce component performance , consider using centralized lubrication manner bearing lubrication, prevent long refueling cycle caused lubrication is not in place , cause bearing damage.
Bearing clearance is too large, easily lead to bearing at runtime to withstand external loads to reduce the number of rollers , roller aggravate pitting wear ; clearance is too small , easily lead to bearing friction heat, temperature, damage film . In many situations is often only a few roller under load , most of the roller in a relaxed state , so when the design selection should consider the impact of the bearing clearance for its life .
2.3 Bearing Vibration Analysis
Wind speed and direction are changing , as appropriate aeroelastic wind wheel prone to twisting and waving other conditions also appear to reverse the drive chain and shimmy phenomenon . Bearing systems ( including housing) as a drive chain subsystem actually an elastic damping dynamics systems. Wind turbine in a stable wind conditions , prone to regular torsional vibration and shimmy , there will be vibration bearing a certain extent . Since the torsional vibration, wear regularity roller holder , and the holder of the material to be ground falls lubricating oil will accelerate wear of the bearing . To reduce bearing vibration damping can be increased throughout the transmission chain from start, to improve the stability of the transmission system , even when the drive chain bearing selection must consider the natural frequency of the drive train and the whole crew , to avoid the natural frequency of the drive chain and external excitation frequency low frequency resonance.
3 Conclusion
The reason our country from the wind turbine wind farm operators into perspective, generating spindle bearing damage except materials and processing technology , but also because of the long-term double-row spindle bearings under extreme wind speeds resulting in separate partial load bearing raceways and cage damage , lubricating bearing components are not in place and cause wear and tear , clearance bearing failure caused by improper design , as well as accelerated wear of the bearing vibration . Due to the complexity of the wind turbine and wind turbine loads , how to further improve the carrying capacity of spindle bearings need to be further studied.