Effects of wind shear on wind turbine rotor loads and planetary bearing reliability

Abstract

Recent studies suggest that wind shear and the resulting pitch moments increase bearing loads and thereby contribute to premature wind turbine gearbox failure. In this paper, we use momentum‐based modeling approaches to predict the pitch moments from wind shear. The non‐dimensionalized results, which have been validated against accepted aeroelastic results, can be used to determine thrust force, pitch moment and power of a general rotor as a function of the wind shear exponent. Even in extreme wind shear (m = 1), the actual thrust force and power for a typical turbine (R* < 0.5) were within 8% and 20% of the nominal values (those without wind shear), respectively. The mean pitch moment increased monotonically with turbine thrust, rotor radius and wind shear exponent. For extreme wind shear (m = 1) on a typical turbine (R* = 0.5), the mean pitch moment is ~25% the product of thrust force and rotor radius. Analysis of wind shear for a typical 750 kW turbine revealed that wind shear does not significantly affect bearing loads because it counteracts the effects of rotor weight. Furthermore, even though general pitch moments did significantly increase bearing loads, they were found to be unlikely to cause bearing fatigue. Analyses of more common low wind‐speed cases suggest that bearing under‐loading and wear are more likely to contribute to premature bearing failure than overloading and classical surface contact fatigue. Copyright © 2015 John Wiley & Sons, Ltd.

Wind turbine main‐bearing loading and wind field characteristics

“…Wind turbine gearboxes on the other hand have received considerable attention in terms of loads, load modelling and the relationship to damage modes. For example, there are papers dealing specifically with gearbox bearing loads in relation to bearing slippage, load measurements, wind shear effects on planetary bearing loads, and contact load fatigue for planetary bearings . The papers mentioned here are just some examples from what is easily described as a vast literature on the subject.…”

“…For example, there are papers dealing specifically with gearbox bearing loads in relation to bearing slippage, load measurements, wind shear effects on planetary bearing loads, and contact load fatigue for planetary bearings. [12][13][14][15] The papers mentioned here are just some examples from what is easily described as a vast literature on the subject. It would therefore seem that there is a considerable knowledge gap when it comes to wind turbine main-bearing science.…”

Comparison of planetary bearing load-sharing characteristics in wind turbine gearboxes

“…Wind power plant O&M averages USD 10 per megawatt hour at recently installed wind plants, accounts for 20 % or more of the wind power purchase agreement price, and generally increases as the wind plant ages (Wiser and Bolinger, 2017). Approximately half of the total wind plant O&M costs are related to wind turbine O&M (Lantz, 2013), and a sizeable portion of these costs is related to the reliability of the wind tur-bine drivetrain (Kotzalas and Doll, 2010;Greco et al, 2013;Keller et al, 2016).…”

Comparison of Planetary Bearing Load-Sharing Characteristics in Wind Turbine Gearboxes

“…The effect of carrier bearing clearance on planetary load sharing subject to rotor moments has also been studied (Crowther et al, 2011, LaCava et al, 2013, Guo et al, 2014. Rotor moments impact planet load sharing, gear and bearing alignment, and bearing contact conditions and stress (Park et al, 2013, Gould and Burris, 2016, Dabrowski and Natarajan, 2017. Rotor 15 moments and gravity result in once-per-revolution effects in the rotating carrier frame, resulting in both increased bearing loads and fatigue and reduced bearing loads potentially causing wear or skidding conditions (Guo et al, 2014, Gould andBurris, 2016).…”

“…Rotor moments impact planet load sharing, gear and bearing alignment, and bearing contact conditions and stress (Park et al, 2013, Gould and Burris, 2016, Dabrowski and Natarajan, 2017. Rotor 15 moments and gravity result in once-per-revolution effects in the rotating carrier frame, resulting in both increased bearing loads and fatigue and reduced bearing loads potentially causing wear or skidding conditions (Guo et al, 2014, Gould andBurris, 2016). Although it is generally agreed that a three-planet gear set with a floating central member has equal load sharing regardless of manufacturing errors (Cooley and Parker, 2014), in the wind turbine application, bearing clearance, gravity, and rotor moments can in fact cause unequal load sharing between planet gears.…”