The effect of electrical current and lubricant formulation on premature white etching crack failures within wind turbine bearings
Premature fatigue failures associated with local regions of microstructural degradation (i.e. White Etching Cracks (WECs)) are the predominate mode of failure within wind turbine drivetrain bearings. Although WECs have been reported in the field for over a decade, the conditions leading to this failure, and the process by which this failure culminates, are both highly debated. Because of this, researchers are often required to turn to non-realistic conditions such as hydrogen charging, or the use of specific, non-wind, lubricant formulations to form these failures at the lab scale. Recently, The United States National Renewable Energy Laboratory instrumented a wind turbine drivetrain and measured numerous potential drivers such as excessive slip, and small electrical currents during turbine operation. The present work, conducted by researchers at Argonne National Laboratory in the United States intends to highlight the effect that these realistic conditions have on the formation of WEC failures at the benchtop scale. It was documented that the levels of electrical current documented uptower are able to significantly accelerate the formation of WECs within several commercially available wind lubricants. However, very small levels of current, <25 mA seem, to have a minimal effect on the formation of WECs by the 300 million contact cycle run out limit. Once the methodology of inducing WECS via these means was established, the effect of lubricant formulation via variable base fluid and additive composition was studied. Moreover, the effect of potential mitigation techniques such as the use of black oxide conversion layers, and other protective coatings will be presented.