A study of grease lubricants under wind turbine pitch bearing conditions

Pitch bearings in wind turbines are affected by reciprocating motion due to pitch control. The combination of oscillating operation, high loads, and mixed lubrication often leads to wear. Grease lubricants in wind turbine pitch bearings should be designed to avoid such wear. Due to different available grease lubricants, the anti-wear properties are investigated under downscaled wind turbine pitch bearing conditions. The downscaling is accomplished by load simulation for a pitch bearing and analysis of the pitch movements for a 7.5 MW reference turbine. The operational conditions of the four point contact ball bearing with 5 m outer diameter are scaled to angular contact ball bearings of the size 7208. The investigations are concluded with contact model experiments. Six Industrial grease lubricants for wind turbine pitch bearings are tested that follow very different compositions. The investigations reveal, that none of the tested grease lubricants was able to reduce wear for all tested conditions. After 250000 cycles certain conditions lead to severe wear. Therefore, the pitch controller should avoid such conditions if possible. Nevertheless, grease lubricants with low base oil viscosities and high bleeding rates are best on average for the tested conditions. Furthermore, the results of the bearing experiments are comparable to the model experiments. © 202

Starvation and Re-lubrication in Oscillating Bearings: Influence of Grease Parameters

A common application for grease-lubricated oscillating rolling element bearings is, e.g., rotor blade bearings in wind turbines. These bearings mainly operate under conditions that are prone to starvation. If the grease is unable to provide enough inlet lubricant supply for the contact between rolling element and bearing raceway, wear in the form of False Brinelling and thus premature bearing failure is possible. Bearing experiments with different lithium complex model greases, which differ mainly in their base oil viscosity and oil separation rate, were carried out to show the influence of the grease parameters on wear initiation. The results show that the ability of the grease to release a high amount of base oil with high mobility into the track of the rolling element is a crucial mechanism to prevent wear, especially at small oscillation angles. For oscillation angles larger than a critical angle, a secondary replenishment mechanism may prevent early wear initiation. The experimental results are used to validate a starvation model proposed in earlier work (Wandel et al. in Tribol Int 165:107276, 2022)

Comparison of Life Calculations for Oscillating Bearings Considering Individual Pitch Control in Wind Turbines

The fatigue life calculation of bearings under rotating conditions has been well researched and standardized. In contrast, for bearings in oscillating applications no international standards exist. As a result, pitch bearings in wind turbines are designed with different, non standardized approaches. Furthermore, the impact of individual pitch control on pitch bearings has not yet been studied. In this paper four approaches for fatigue life calculation will be applied and compared under individual pitch control conditions. For comparison, the loads and the bearing geometry of the reference turbine IWT 7.5 MW, which is individual pitch controlled, are used. This paper will show how the bearing life calculated by different approaches reacts to individual pitch control conditions. Furthermore, the factors for the modified rating life, according to the ABMA and ISO standards, which implement different operation conditions on the bearings in rotating applications, are calculated for the given loads and the given bearing geometry in oscillating applications

Investigations Regarding the Operating Performance of OscillatingBearings using the Example of Wind Turbine Pitch Bearings

Pitch bearings in wind turbines are typical examples for oscillating rollingelement bearings. On the one hand pitch bearings are aected by intentionaloscillations due to the adaption of the aerodynamic angle of attack of the rotorblade. On the other hand, unwanted micro-oscillations (vibrations) are causedby turbulence when the wind turbine is at standstill. The occurring damagemechanisms can reduce the service life of component and, in the worst casescenario, lead to a failure of the whole technical system.On basis of the operating conditions of a reference wind turbine and loadsimulations for the reference pitch bearing, the occurring wear phenomena areanalysed. For this purpose, experimental investigations for the identicationand determination of inuencing parameters are undertaken. The experimentalinvestigations are carried out on angular contact ball bearings of the size7208. The operating conditions of the reference pitch bearing are transferredto the test bearing size using a scaling method. A time-dependent connectionof wear phenomena is established by the incubation hypotheses. The inuenceof the oscillation amplitude and frequency on occurring wear becomesclear through the investigations. In addition, experiments are carried out onfour-point contact ball bearing with a pitch diameter of 675 mm.The results of the experimental investigations are used to set up a simulationmodel which is focused on the contact kinematics between rolling elementsand raceways. The occurrence and the form of the wear can be explainedwith the simulated frictional work. Using the fully parametric structure of themodel, the inuence of the bearing geometry and input parameters on thefrictional work can be analysed.In order to determine the inuence of the type of lubricating grease, afurther series of experiments is carried out. In this experiments common usedlubricants for pitch bearings are tested. The results show that none of theexamined lubricants can prevent wear for all operating conditions. However,statements on suitable grease compositions can be made for certain operatingparameters.The results show the relationship between wear and operating parametersin pitch bearings based on experimental investigations and simulations.Rotorblattlager in Windenergieanlagen sind typische Beispiele für oszillierendeWälzlager. Zum einem werden Rotorblattlager gewollten Oszillationenausgesetzt, um den aerodynamischen Angriswinkel des Rotorblattes einzustellen.Zum anderem entstehen ungewollte Mikrooszillationen (Vibrationen)durch Turbulenzen, wenn die Windenergieanlage stillsteht. Durch Oszillationenaufkommende Schadensmechanismen können die Gebrauchsdauer der Maschinenkomponentereduzieren und im schlimmsten Fall zum Ausfall des Gesamtsystemsführen.Auf Basis des Betriebsverhaltens einer Referenzwindenergieanlage und Lastsimulationenfür das zugehörige Referenzrotorblattlager werden verschiedeneVerschleiÿphänomene analysiert. Zu diesem Zweck werden experimentelle Untersuchungenzur Identikation und Ermittlung von Einussparametern unternommen.Die experimentellen Untersuchungen werden an Schrägkugellagernder Baugröÿe 7208 durchgeführt. Die Betriebsbedingungen des Referenzrotorblattlagerswerden mit Hilfe einer Skalierungsmethode auf die Prüagergrö-ÿe übertragen. Ein zeitlicher Zusammenhang der Verschleiÿphänomene wirddurch die Inkubationshypothese hergestellt. Der Einuss der Oszillationsamplitudeund -frequenz wird durch die Untersuchungen deutlich. Darüber hinauswerden Untersuchungen an Vierpunktlagern mit einem Laufkreisdurchmesservon 675 mm durchgeführt.Auf Basis der Ergebnisse der experimentellen Untersuchungen wird einSimulationsmodell aufgebaut, welches die Kinematik des Kontakts zwischenWälzkörper und Laufbahn abbildet. Das Auftreten und die Form des Verschleiÿes können mit Hilfe der Reibarbeit erklärt werden. Mit Hilfe des parametrischenAufbaus des Modells, kann der Einuss der Lagergeometrie undder Eingangsparameter auf die Reibarbeitsdichte analysiert werden.Um den Einuss des Schmiermittels bestimmen zu können wird eine weitereVersuchsreihe durchgeführt. In dieser Versuchsreihe werden gängige Schmierfettefür Rotorblattlager getestet. Die Ergebnisse zeigen, dass keines der untersuchtenSchmierfette für alle Betriebsbedingungen Verschleiÿ verhindern kann.Allerdings lassen sich für bestimmte Betriebsparameter Aussagen zur geeignetenFettzusammenstellungen treen.Die Ergebnisse der vorliegenden Arbeit zeigen den Zusammenhang zwischenVerschleiÿ und Betriebsparametern in Rotorblattlagern anhand experimentellerUntersuchungen und Simulationen.QC 20200602</p

Investigations Regarding the Operating Performance of OscillatingBearings using the Example of Wind Turbine Pitch Bearings

Pitch bearings in wind turbines are typical examples for oscillating rollingelement bearings. On the one hand pitch bearings are aected by intentionaloscillations due to the adaption of the aerodynamic angle of attack of the rotorblade. On the other hand, unwanted micro-oscillations (vibrations) are causedby turbulence when the wind turbine is at standstill. The occurring damagemechanisms can reduce the service life of component and, in the worst casescenario, lead to a failure of the whole technical system.On basis of the operating conditions of a reference wind turbine and loadsimulations for the reference pitch bearing, the occurring wear phenomena areanalysed. For this purpose, experimental investigations for the identicationand determination of inuencing parameters are undertaken. The experimentalinvestigations are carried out on angular contact ball bearings of the size7208. The operating conditions of the reference pitch bearing are transferredto the test bearing size using a scaling method. A time-dependent connectionof wear phenomena is established by the incubation hypotheses. The inuenceof the oscillation amplitude and frequency on occurring wear becomesclear through the investigations. In addition, experiments are carried out onfour-point contact ball bearing with a pitch diameter of 675 mm.The results of the experimental investigations are used to set up a simulationmodel which is focused on the contact kinematics between rolling elementsand raceways. The occurrence and the form of the wear can be explainedwith the simulated frictional work. Using the fully parametric structure of themodel, the inuence of the bearing geometry and input parameters on thefrictional work can be analysed.In order to determine the inuence of the type of lubricating grease, afurther series of experiments is carried out. In this experiments common usedlubricants for pitch bearings are tested. The results show that none of theexamined lubricants can prevent wear for all operating conditions. However,statements on suitable grease compositions can be made for certain operatingparameters.The results show the relationship between wear and operating parametersin pitch bearings based on experimental investigations and simulations.Rotorblattlager in Windenergieanlagen sind typische Beispiele für oszillierendeWälzlager. Zum einem werden Rotorblattlager gewollten Oszillationenausgesetzt, um den aerodynamischen Angriswinkel des Rotorblattes einzustellen.Zum anderem entstehen ungewollte Mikrooszillationen (Vibrationen)durch Turbulenzen, wenn die Windenergieanlage stillsteht. Durch Oszillationenaufkommende Schadensmechanismen können die Gebrauchsdauer der Maschinenkomponentereduzieren und im schlimmsten Fall zum Ausfall des Gesamtsystemsführen.Auf Basis des Betriebsverhaltens einer Referenzwindenergieanlage und Lastsimulationenfür das zugehörige Referenzrotorblattlager werden verschiedeneVerschleiÿphänomene analysiert. Zu diesem Zweck werden experimentelle Untersuchungenzur Identikation und Ermittlung von Einussparametern unternommen.Die experimentellen Untersuchungen werden an Schrägkugellagernder Baugröÿe 7208 durchgeführt. Die Betriebsbedingungen des Referenzrotorblattlagerswerden mit Hilfe einer Skalierungsmethode auf die Prüagergrö-ÿe übertragen. Ein zeitlicher Zusammenhang der Verschleiÿphänomene wirddurch die Inkubationshypothese hergestellt. Der Einuss der Oszillationsamplitudeund -frequenz wird durch die Untersuchungen deutlich. Darüber hinauswerden Untersuchungen an Vierpunktlagern mit einem Laufkreisdurchmesservon 675 mm durchgeführt.Auf Basis der Ergebnisse der experimentellen Untersuchungen wird einSimulationsmodell aufgebaut, welches die Kinematik des Kontakts zwischenWälzkörper und Laufbahn abbildet. Das Auftreten und die Form des Verschleiÿes können mit Hilfe der Reibarbeit erklärt werden. Mit Hilfe des parametrischenAufbaus des Modells, kann der Einuss der Lagergeometrie undder Eingangsparameter auf die Reibarbeitsdichte analysiert werden.Um den Einuss des Schmiermittels bestimmen zu können wird eine weitereVersuchsreihe durchgeführt. In dieser Versuchsreihe werden gängige Schmierfettefür Rotorblattlager getestet. Die Ergebnisse zeigen, dass keines der untersuchtenSchmierfette für alle Betriebsbedingungen Verschleiÿ verhindern kann.Allerdings lassen sich für bestimmte Betriebsparameter Aussagen zur geeignetenFettzusammenstellungen treen.Die Ergebnisse der vorliegenden Arbeit zeigen den Zusammenhang zwischenVerschleiÿ und Betriebsparametern in Rotorblattlagern anhand experimentellerUntersuchungen und Simulationen.QC 20200602</p