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{{short description|Component connecting a turbine blade to the hub allowing pitch variation}}
{{DISPLAYTITLE:Pitch bearing}}
[[File:Hub_secured_to_Turbine_Tower_No_11_-_geograph.org.uk_-_787507.jpg|thumb|Rotor hub and pitch bearing without mounted rotor blades]]
The '''[[Blade pitch|pitch]] [[Bearing (mechanical)|bearing]]''', also named blade bearing, is a component of modern [[wind turbine]]s which connect the rotor hub and the rotor blade.<ref>{{Cite book|title=Wind Energy Handbook - Burton - Wiley Online Library|last=Burton|first=Tony|last2=Sharpe|first2=David|last3=Jenkins|first3=Nick|last4=Bossanyi|first4=Ervin|language=en|doi=10.1002/0470846062|year = 2001|isbn = 978-0471489979}}</ref> The bearing allows the required oscillation to control the loads and power of the wind turbine. The pitch system brings the blade to the desired position by adapting the aerodynamic [[angle of attack]].<ref>{{Cite web|url=https://www.researchgate.net/publication/309585771|title=Service Life of Blade Bearings - Problems Faced in Service Life Estimation of Blade Bearings|last=Schwack|first=Fabian|last2=Poll|first2=Gerhard|website=ResearchGate|language=en|access-date=2017-07-19}}</ref> The pitch system is also used for emergency breaks of the turbine system.<ref>{{Cite web|url=https://www.dnvgl.com/energy/standards-guidelines/rc-gl-certification-wind-turbines-cn.html|title=Certification of Wind Turbines - DNV GL|website=DNV GL|access-date=2017-07-19}}</ref>

== Design ==
[[File:Size_comparison_child_in_wind_turbine_rotor_hub_without_blades_(enercon_e-70).jpg|thumb|Size comparison: Child in wind turbine rotor hub without blades]]
[[File:Vierpunktlager_pitchlager_prigge_schwack.png|thumb|One row four point contact ball bearing with gear spur for the pitch drive]]
Mostly large [[Rolling-element bearing|rolling element bearing]] are used as pitch bearings.<ref>{{Cite web|url=http://webcache.googleusercontent.com/search?q=cache:hbp1QJyfdosJ:citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.610.8882&rep=rep1&type=pdf+&cd=1&hl=de&ct=clnk&gl=de|title=Wind Turbine Design Guideline DG03: Yaw and Pitch Rolling Bearing Life|last=NREL|first=T. Harris, J.H. Rumbarger, and C.P. Butterfield|website=webcache.googleusercontent.com|access-date=2017-07-19}}</ref> The bearing is subjected to high [[bending moment]]s, radial and axial loads in both directions. Therefore, the rolling elements for [[state of the art]] wind turbines are ball bearings, which are used in a double rowed four-point contact. This means each raceway carries on two points, and in sum four points are carrying. Other possible options are different arrangements of the rolling elements or multirow cylindrical roller bearings.<ref>{{Cite book|title=Wind Energy Handbook - Burton - Wiley Online Library|last=Burton|first=Tony|last2=Sharpe|first2=David|last3=Jenkins|first3=Nick|last4=Bossanyi|first4=Ervin|language=en|doi=10.1002/0470846062|year = 2001|isbn = 978-0471489979}}</ref> Pitch bearing of modern wind turbines can reach diameters of more than 4 meters.<ref>{{Cite journal|last=Schwack|first=F.|last2=Stammler|first2=M.|last3=Poll|first3=G.|last4=Reuter|first4=A.|date=2016|title=Comparison of Life Calculations for Oscillating Bearings Considering Individual Pitch Control in Wind Turbines|url=http://stacks.iop.org/1742-6596/753/i=11/a=112013|journal=Journal of Physics: Conference Series|language=en|volume=753|issue=11|pages=112013|doi=10.1088/1742-6596/753/11/112013|issn=1742-6596|bibcode=2016JPhCS.753k2013S|doi-access=free}}</ref>

Change of the lubricants can be carried out only with great time and cost expenditure. Furthermore, due to the constant rotation of the hub, the used lubricant must remain in place. Therefore, the pitch bearings in wind turbines are usually lubricated with [[Grease (lubricant)|grease]]. The bearing experiences a wide range of operating conditions during operation. Therefore, the operating conditions are very difficult for greases over the entire turbine time. The industrial greases that have been used so far have very different compositions and do not always lead to the desired result of preventing wear.<ref>{{Cite journal|last=Schwack|first=Fabian|last2=Bader|first2=Norbert|last3=Leckner|first3=Johan|last4=Demaille|first4=Claire|last5=Poll|first5=Gerhard|date=2020-08-15|title=A study of grease lubricants under wind turbine pitch bearing conditions|url=http://www.sciencedirect.com/science/article/pii/S0043164819318514|journal=Wear|language=en|volume=454-455|pages=203335|doi=10.1016/j.wear.2020.203335|issn=0043-1648|doi-access=free}}</ref>

== Load situation ==

The load and operating situation of pitch bearings are for rolling element bearings comparatively unfavorable. The bearings are exposed to high loads and small [[Reciprocating motion|reciprocating]] movements created by the pitch system or [[vibration]]s from the [[Wind|wind profile]]. The small reciprocating movements between rolling elements and raceway can lead to wear phenomena like [[false brinelling]] and [[Fretting|fretting corrosion]].<ref>{{Cite web|url=https://www.researchgate.net/publication/316543220|title=Time-dependent analyses of wear in oscillating bearing applications (PDF Download Available)|last=Schwack|first=Fabian|last2=Artjom|first2=Byckov|date=2017-05-25|website=ResearchGate|language=en|access-date=2017-07-19|last3=Bader|first3=Norbert|last4=Poll|first4=Gerhard}}</ref> Furthermore, the high loads can lead to [[Truncation (geometry)|truncation]] of the contact ellipse.<ref>{{Cite web|url=https://www.researchgate.net/publication/308890408|title=Free Contact Angles in Pitch Bearings and their Impact on Contact and Stress Conditions (PDF Download Available)|last=Schwack|first=Fabian|last2=Stammler|first2=Matthias|date=2016-09-26|website=ResearchGate|language=en|access-date=2017-07-19|last3=Flory|first3=Heiko|last4=Poll|first4=Gerhard}}</ref> Due to the small reciprocating movements calculation methods to estimate the [[Fatigue (material)|bearing service life]] <ref>{{Cite journal|last=Schwack|first=F.|last2=Stammler|first2=M.|last3=Poll|first3=G.|last4=Reuter|first4=A.|date=2016|title=Comparison of Life Calculations for Oscillating Bearings Considering Individual Pitch Control in Wind Turbines|url=http://stacks.iop.org/1742-6596/753/i=11/a=112013|journal=Journal of Physics: Conference Series|language=en|volume=753|issue=11|pages=112013|doi=10.1088/1742-6596/753/11/112013|issn=1742-6596|bibcode=2016JPhCS.753k2013S|doi-access=free}}</ref> and the [[friction torque]]<ref>{{Cite journal|last=Stammler|first=Matthias|last2=Schwack|first2=Fabian|last3=Bader|first3=Norbert|last4=Reuter|first4=Andreas|last5=Poll|first5=Gerhard|title=Friction torque of wind-turbine pitch bearings &ndash; comparison of experimental results with available models|journal=Wind Energy Science Discussions|pages=1–16|doi=10.5194/wes-2017-20|year=2017|doi-access=free}}</ref> are not usable for pitch bearings. Newer controlling concepts of pitch control, like individual pitch control, will lead to a different operating behavior<ref>{{Cite journal|last=Bossanyi|first=E. A.|date=2003-04-01|title=Individual Blade Pitch Control for Load Reduction|journal=Wind Energy|language=en|volume=6|issue=2|pages=119–128|doi=10.1002/we.76|issn=1099-1824|bibcode=2003WiEn....6..119B}}</ref> which in worst could favor false brinelling and fretting corrosion <ref>{{Cite web|url=https://www.researchgate.net/publication/317004158|title=Frictional Work in Oscillating Bearings – Simulation of an Angular Contact Ball Bearing under Dry Conditions and Small Amplitudes|last=Schwack|first=Fabian|last2=Prigge|first2=Felix|website=ResearchGate|language=en|access-date=2017-07-19|last3=Poll|first3=Gerhard}}</ref> or in best case reduce such wear.<ref>{{Cite journal|last=Stammler|first=Matthias|last2=Thomas|first2=Philipp|last3=Reuter|first3=Andreas|last4=Schwack|first4=Fabian|last5=Poll|first5=Gerhard|date=2020|title=Effect of load reduction mechanisms on loads and blade bearing movements of wind turbines|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/we.2428|journal=Wind Energy|language=en|volume=23|issue=2|pages=274–290|doi=10.1002/we.2428|issn=1099-1824|doi-access=free}}</ref>

[[File:Fretting_And_FalseBrinelling_Schwack_Byckov.png|thumb|False brinelling and fretting corrosion |center|440x440px]]

==References==
{{reflist}}

{{Wind power}}

[[Category:Bearings (mechanical)]]
[[Category:Wind turbines]]

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Admin: 1 revision imported: Mitul Imported from Wikipedia

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