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Causes of Early Failure of Wind Turbine Bearings-Overload or Underload?

2021-03-31 09:34

Wind turbines and their components have been carefully designed to operate for more than 20 years. According to the industry standard DIN ISO281 bearing rating life calculation method, the life of roller bearings and (C1/P)10/3Proportional, where C is the bearing dynamic load rating and P is the working load. Based on the rated dynamic load of the wind turbine bearing and its expected working load, the bearing should have high reliability within the expected service life,In fact, wind turbine gearbox bearings often fail within 2 to 11 years, mainly caused by high-speed shaft bearings, medium-speed shaft bearings and planetary gear bearings. Planet wheel bearing failure becomes a major problem, Unlike the high-speed shaft and medium-speed shaft bearings that can be replaced on the tower, the replacement of planetary wheel bearings requires the use of a crane to disassemble, transport and repair the gearbox off-site. The direct cost of loss of revenue and replacement during downtime greatly increases the cost of wind power generation, which is the demand for fossil fuels, CO.2Emissions and energy sustainability have a negative impact.

 

The early failure of gearbox bearings is not due to the use of inappropriate materials or inadequate integration of design and practice. Musial et al. concluded that the most likely explanation for the failure is that important loading conditions were not considered during the design process. Since industry standards assume that load is inversely proportional to life, it is reasonable to assume that early bearing failures are caused by bearing overloads that are difficult to predict, model, or detect.Storm winds, gusts, start-stop transients, grid faults, and wind shear all have a significant and unpredictable impact on bearing loads and reliability.

     The tribological relative motion between two contact bodies can be described by sliding, rolling or a combination of the two. The slip-to-roll ratio (SRR) can be used to characterize the position of the rolling body somewhere in the spectrum from rolling to sliding, and the SRR of pure rolling and pure sliding are 0 and 2, respectively. Sliding often causes rapid and unpredictable wear, and the failure of pure rolling contact is the result of rolling contact fatigue and can be predicted by DINISO281. The SRR of cylindrical roller bearings for wind turbines increases at low loads due to the drag force required to maintain the rolling state. The results of Kang et al. show that when C1When/P increases from 1 to 2000, the SRR of cylindrical roller bearings for wind turbines will increase by an order of magnitude or more. That is, slip becomes more prevalent when the dynamic load rating is several orders of magnitude greater than the operating load. Therefore, in order to prevent excessive skidding, wear and unpredictable shortening of bearing life, many bearing manufacturers specifyMinimum load rating.

 

Inspection and analysis show that the failure of the bearing is mainly due to excessive slip and wear caused by pitting, smearing and white erosion spalling. Gould and Greco believe that the bearing reaction force is not sufficient to provide the drag force required for rolling. The potential factor is the variability of the load caused by changes in wind speed. The bearing design must consider the extreme load of the bearing, which is obviously rarely the case. Under the more common wind speed conditions, when the load is low, the SRR increases, and excessive slip increases the risk of bearing surface damage.

     Direct measurements by Guo et al. using the instrumented drive system show that the planetary drive system supports most of the non-torque loads caused by cantilever rotor weight, wind shear, yaw, and other potential factors. The mechanical dynamics model of the gearbox using the Gearbox Reliability Cooperation (GRC) standard gearbox shows that the transfer of non-torque loads to the planetary transmission system is mainly related to the clearance of the planet carrier cylindrical bearing. Independent analyses by Guo et al. and Gould and Burris show that the non-torque load distribution of the planetary drive system simultaneously increases or decreases the planetary bearing reaction force during different phases of the carrier's operation. The non-torque load distributed by the planetary transmission system further reduces the already small working load under normal wind conditions.Common transient events (such as grid failure and wind gusts) may cause the rolling element to slip suddenly, and the underload can cause the bearing to be easily damaged.

      Direct measurements by Guo et al. using the instrumented drive system show that the planetary drive system supports most of the non-torque loads caused by cantilever rotor weight, wind shear, yaw, and other potential factors. The mechanical dynamics model of the gearbox using the Gearbox Reliability Cooperation (GRC) standard gearbox shows that the transfer of non-torque loads to the planetary transmission system is mainly related to the clearance of the planet carrier cylindrical bearing. Independent analyses by Guo et al. and Gould and Burris show that the non-torque load distribution of the planetary drive system simultaneously increases or decreases the planetary bearing reaction force during different phases of the carrier's operation. The non-torque load distributed by the planetary transmission system further reduces the already small working load under normal wind conditions.Common transient events (such as grid failure and wind gusts) may cause the rolling element to slip suddenly, and the underload can cause the bearing to be easily damaged.