Experimental Investigations on Wear in Oscillating Grease-Lubricated Rolling Element Bearings of Different Size and Type

Grease-lubricated rolling element bearings can suffer from wear due to lubricant starvation under certain oscillating operating conditions. Especially for large-scale slewing bearings, such as blade bearings in wind turbines, experimental investigations are complex compared to small-scale reference testing. For an easier manner of testing, it is desirable to know whether the results of small-scale testing are applicable to larger-sized bearings. In this work, three different bearing types were tested and compared to already published results from a small-scale ACBB with a pitch diameter of 60 mm. The newly tested bearing types comprise a downscaled blade bearing (4-point contact double row ball bearing) with a pitch diameter of 673 mm, a small-scale CRTB with a pitch diameter of 77.5 mm and another ACBB with a pitch diameter of 95 mm. Qualitatively, all tested bearings show similar wear behaviour in terms of friction energy when operation parameters are varied. With higher oscillation frequency, damage becomes more severe. The oscillation amplitude shows three distinctive regimes. Within the range of small amplitudes, an increase in amplitude leads to more pronounced damage. We observe a threshold amplitude where this is no longer the case; a further increase in amplitude counteracts wear initiation until a final threshold is reached, beyond which no more wear is observed. These findings are in accordance with the reference results of the small-scale ACBB. Direct comparison between point and line contact shows that the latter is more prone to wear initiation under grease-lubricated, oscillating operating conditions. Furthermore, a previously introduced empirical number shows good performance in assessing critical operating parameters of the different bearing types. Specifically, harmful operating conditions can be classified for all studied bearing types with an accuracy of 78%. This method can be useful to assess operating conditions of greased, oscillating, rolling element bearings, e.g., to assess different pitch controllers or designs of slewing bearings

Wear Development in Oscillating Rolling Element Bearings

Rotor blade bearings enable rotor blades to pivot about their longitudinal axis and thus control the power output and reduce the loads acting on the wind turbine. Over a design period of 20 years, rolling bearings are exposed to frequent oscillation movements with amplitude ratios of x/2b > 1, especially due to new control concepts such as Individual Pitch Control, which can lead to wear and a reduction in service life. The objective of this paper was to identify the dominant wear mechanisms and their consequences for the operation of oscillating bearings. Oscillating experiments with an increasing number of cycles on the angular contact ball bearings of two different sizes (types 7208 and 7220) show that the damage initiation starts with adhesive and corrosive wear mechanisms, which result in a sharp increase in the torque as well as the wear volume on the bearing raceway. As the number of cycles increases, an abrasive mechanism occurs, resulting in a lower slope of the wear curve and a smoothing of the resulting wear depressions. The wear and torque curves were evaluated and classified using an energy-wear approach according to Fouvry

Analysis of Dynamic Interactions between Different Drivetrain Components with a Detailed Wind Turbine Model

The presented work describes a detailed analysis of the dynamic interactions among mechanical and electrical drivetrain components of a modern wind turbine under the influence of parameter variations, different control mechanisms and transient excitations. For this study, a detailed model of a 2MW wind turbine with a gearbox, a permanent magnet synchronous generator and a full power converter has been developed which considers all relevant characteristics of the mechanical and electrical subsystems. This model includes an accurate representation of the aerodynamics and the mechanical properties of the rotor and the complete mechanical drivetrain. Furthermore, a detailed electrical modelling of the generator, the full scale power converter with discrete switching devices, its filters, the transformer and the grid as well as the control structure is considered. The analysis shows that, considering control measures based on active torsional damping, interactions between mechanical and electrical subsystems can significantly affect the loads and thus the individual lifetime of the components

Converter Lifetime Assessment for Doubly-Fed Induction Generators Considering Derating Control Strategies at Low Rotor Frequencies

In this paper, various control strategies around the synchronous operating point with the aim to reduce the thermal loading of the rotor-side converter in wind turbines equipped with doubly-fed induction generators are investigated regarding their assets and drawbacks. It is shown that there are various possibilities to prolong the lifetime expectation of the converter regarding its thermal stress by implementing these control strategies. However, every control measure requires a careful design process or a slight adjustment of the system to ensure a positive effect on the overall behaviour of the wind turbine

#IOeG2016 | Holger Berwinkel: Probleme einer Aktenkunde der Zeitgeschichte

Im Vorfeld der Jahrestagung 2016 des Instituts für Österreichische Geschichtsforschung „Die Zukunft der Vergangenheit in der Gegenwart. Archive als Leuchtfeuer im Informationszeitalter“ werden an dieser Stelle die Abstracts zu den Vorträgen der Reihe nach zugänglich gemacht. Nachstehend das Abstract von Holger Berwinkel (Politisches Archiv des Auswärtigen Amts, Berlin; Blog „Aktenkunde“) zu seinem Beitrag „Probleme einer Aktenkunde der Zeitgeschichte“: Die Aktenkunde dient der Klärung zeitlos..

Impact of individual pitch control on pitch actuators in megawatt wind turbines

Individual pitch control is seen as a promising control technique for load reduction of the rotor blades in megawatt wind turbines. As the rotor blades are getting bigger and bigger, the asymmetric loads due to wind speed variations across the rotor area are increasing, too. Modern wind turbines include individual pitch actuators for every blade and the control effort is also reasonable. This is why a lot of research has been done on individual blade pitch control strategies and their impact on load reduction and further stress of the mechanical components, such as pitch bearings. The present work shows that individual pitch control is able to reduce mechanical fatigue loads, however, it affects the dynamic loads of the pitch motors and might lead to an increased overall stress of their power electronic converters

Solutions to reduce wear in wind turbine blade bearings

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