A review of wind turbine main bearings: design, operation, modelling, damage mechanisms and fault detection

Abstract

This paper presents a review of existing theory and practice relating to main bearings for wind turbines. The main bearing performs the critical role of supporting the turbine rotor, with replacements typically requiring its complete removal. The operational conditions and loading for wind turbine main bearings deviate significantly from those of more conventional power plants and other bearings present in the wind turbine power train, i.e. those in the gearbox and generator. This work seeks to thoroughly document current main-bearing theory in order to allow for appraisal of existing design and analysis practices, while also seeking to form a solid foundation for future research in this area. The most common main-bearing setups are presented along with standards for bearing selection and rating. Typical loads generated by a wind turbine rotor, and subsequently reacted at the main bearing, are discussed. This is followed by the related tribological theories of lubrication, wear and associated failure mechanisms. Finally, existing techniques for bearing modelling, fault diagnosis and prognosis relevant to the main bearing are presented.Published by Copernicus Publications on behalf of the European Academy of Wind Energy e.V.

Developing a systematic approach to the analysis of time‐varying main bearing loads for wind turbines

“…For a low-speed shaft with speed of , wind turbine drivetrains are known to experience load fluctuations at a frequency of 3 , owing to the symmetry of having three blades. 2 It therefore seems intuitive that repeated load patterns at a point on the shaft might also manifest at this same frequency. Having identified full loops, one can determine the angular speed at which that loop was traversed around its centre, denoted 'loop speed', using initial and final time stamp values.…”

“…2. For a partial loop that is fitted well by an elliptical model where data are present, a high value would be expected for R 2 A , whereas a low value would be expected for R 2 B . 3.…”

“…It follows that this score cannot, in isolation, be used to differentiate between full and partial loop cases because, in the latter, the 'gap' in measured data with respect to the ellipse is not taken into account. This issue has been solved by defining a second goodness of fit score, denoted R 2 B , which can be used in conjunction with R 2 A to delineate between loop cases. Conceptually, where R 2 A was constructed by taking each measured data point in turn and asking 'how close is the nearest point on the ellipse', R 2 B will instead be defined such that it is taking each point around the ellipse in turn and asking 'how close is the nearest point in the measured data'.…”

“…1. For a full loop that is fitted well by an elliptical model, high values would be expected for both R 2 A and R 2 B . 2.…”

Constructing fast and representative analytical models of wind turbine main bearings

“…9a. The set of equations for the new analytical model are statically indeterminate, and so the model must be decoupled to find a solution (Hibbeler, 2011;Leet and Uang, 2011). The model was first simplified by moving the location of the force applied by the rotor mass, B, and associated overturning moment, M, to be positioned at the bearing support mount as shown in Fig.…”