Planetary gear load sharing of wind turbine drivetrains subjected to non‐torque loads

An analytical formulation was developed to estimate the load‐sharing and planetary loads of a three‐point suspension wind turbine drivetrain considering the effects of non‐torque loads, gravity and bearing clearance. A three‐dimensional dynamic drivetrain model that includes mesh stiffness variation, tooth modifications and gearbox housing flexibility was also established to investigate gear tooth load distribution and non‐linear tooth and bearing contact of the planetary gears. These models were validated with experimental data from the National Renewable Energy Laboratory's Gearbox Reliability Collaborative. Non‐torque loads and gravity induce fundamental excitations in the rotating carrier frame, which can increase gearbox loads and disturb load sharing. Clearance in the carrier bearings reduces the bearing stiffness significantly. This increases the amount of pitching moment transmitted from the rotor to the gear meshes and disturbs the planetary load share, thereby resulting in edge loading. Edge loading increases the likelihood of tooth pitting and planet‐bearing fatigue, leading to reduced gearbox life. Additionally, at low‐input torque, the planet‐bearing loads are often less than the minimum recommended load and thus susceptible to skidding. Copyright © 2014 John Wiley & Sons, Ltd.     

Improving wind turbine drivetrain designs to minimize the impacts of non‐torque loads

Non‐torque loads induced by the wind turbine rotor overhang weight and aerodynamic forces can greatly affect drivetrain loads and responses. If not addressed properly, these loads can result in a decrease in gearbox component life. This work uses analytical modeling, computational modeling and experimental approaches to evaluate two distinct drivetrain designs that minimize the effects of non‐torque loads on gearbox reliability: a modified three‐point suspension drivetrain studied by the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC) and the Pure Torque® drivetrain developed by Alstom. In the original GRC drivetrain, the unequal planetary load distribution and sharing were present and they can lead to gear tooth pitting and reduce the lives of the planet bearings. The NREL GRC team modified the original design of its drivetrain by changing the rolling element bearings in the planetary gear stage. In this modified design, gearbox bearings in the planetary gear stage are anticipated to transmit non‐torque loads directly to the gearbox housing rather than the gears. Alstom's Pure Torque drivetrain has a hub support configuration that transmits non‐torque loads directly into the tower rather than through the gearbox as in other design approaches. An analytical model of Alstom's Pure Torque drivetrain provides insight into the relationships among turbine component weights, aerodynamic forces and the resulting drivetrain loads. In Alstom's Pure Torque drivetrain, main shaft bending loads are orders of magnitude lower than the rated torque and hardly affected by wind speed, gusts or turbine operations. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of floating sun gear in a wind turbine's planetary gearbox with geometrical imperfections

This paper addresses the effect of gear geometrical errors in wind turbine planetary gearboxes with a floating sun gear. Numerical simulations and experiments are employed throughout the study. A National Renewable Energy Laboratory 750 kW gearbox is modelled in a multibody environment and verified using the experimental data obtained from a dynamometer test. The gear geometrical errors, which are both assembly dependent and assembly independent, are described, and planet‐pin misalignment and eccentricity are selected as the two most influential and key errors for case studies. Various load cases involving errors in the floating and non‐floating sun gear designs are simulated, and the planet‐bearing reactions, gear vibrations, gear mesh loads and bearing fatigue lives are compared. All tests and simulations are performed at the rated wind speed. For errorless gears, the non‐floating sun gear design performs better in terms of gear load variation, whereas the upwind planet bearing has more damage. In the floating sun gear scenario, the planet misalignment is neutralized by changing the sun motion pattern and the planet gear's elastic deformation. The effects of gear profile modifications are also evaluated, revealing that profile modifications such as crowning improve the effects of misalignment. Copyright © 2014 John Wiley & Sons, Ltd.     

计入齿圈柔性的风电机组行星传动动态特性研究

为研究齿圈柔性对风电机组行星齿轮传动系统动态特性的影响,将连续体的柔性齿圈离散成多段刚性轮齿段,以连接处的扭簧扭转刚度来量化齿圈的柔性特点。在行星架随动坐标系下,综合考虑啮合刚度、支撑刚度和齿圈柔性等因素,建立计入齿圈柔性的行星传动系统平移—扭转耦合动力学模型,继而分析齿圈柔性、齿圈支撑点数目与负载力矩对齿圈变形及系统啮合力的影响,并进一步揭示太阳轮浮动轨迹在不同齿圈支撑点数目下的表现特点。研究结果表明:工作过程中的柔性齿圈产生较大的弹性变形,致使太阳轮与行星轮啮合力幅值出现长周期波动,且其频谱中出现多个转频成分,经对比发现该转频分别为行星架转频、ζ倍行星架转频及2ζ倍行星架转频(ζ为齿圈支撑点数目)。当支撑点数目与行星轮个数满足倍数关系时,太阳轮浮动轨迹较为规律,其外轮廓与刚性齿圈条件下一致;否则,浮动轨迹外轮廓呈现出具有ζ个瓣叶的花瓣状。     

750 kW风力机组齿轮箱动力学仿真分析

风力发电机组系统运行时产生剧烈的振动,对齿轮箱的运行精度和齿轮寿命的影响非常大。针对这一情况,文章对齿轮箱进行了重新设计、建模。基于多体系统动力学方法、模态振动、冲击-接触理论,以750 kW型风机齿轮箱为研究对象,通过对齿轮箱的仿真分析,得出齿轮啮合和碰撞力以及动能随时间的变化曲线。文章还对高速齿轮轴进行了模态分析,得到弯曲模态振型图,并将高速齿轮轴、行星轮、行星架和齿轮Z1变为柔体进行应力分析,得到齿轮的应力分布图,为齿轮箱总体动力学特性分析及齿轮箱优化设计奠定基础。     

On the definition and effect of optimum gear microgeometry modifications for the gearbox of an offshore 10-MW wind turbine

This work develops an optimization algorithm for the definition of gear microgeometry modifications (MGM) on a gearbox belonging to an offshore 10-MW wind turbine. Subsequently, the impact of the gear microgeometry on the performance of gears and bearings is quantified: First, under rated load conditions and, second, accounting for the environmental conditions to estimate the long-term damage. To fulfil this task, a high-fidelity numerical model of the drivetrain is used, which meets the design requirements of the Technical University of Denmark (DTU) 10-MW reference offshore wind turbine. The optimization achieves a uniform distribution of the contact stress along the tooth flank, shifts its maximum value to the central position, and eliminates edge contact. These enhancements increase the gear safety factors. Nevertheless, the most significant improvement concerns planetary bearings, for which optimum gear MGM achieve a homogeneous share of the load among bearings. Moreover, deviations of the microgeometry with respect to the defined optimum are also addressed. In gears, lead slope deviations are counteracted by crowning modifications to restrain the increase of the load offset. Concerning planetary bearings, slope deviations can be beneficial or detrimental depending on whether they overload downwind or upwind planetary bearings, respectively. Finally, accumulated damage to planetary bearings after 20 years of service is assessed. Before MGM, results predict a premature failure of planetary bearings, while optimum MGM extend their predicted life above 20 years by achieving a reduction of the maximum accumulated fatigue damage by a factor of 4.4.     

考虑齿圈柔性的风电行星轮系动态啮合特性研究

针对集中参数法难以考虑齿圈柔性而有限元法计算量大的问题,以风电行星轮系为研究对象在集中参数/有限元混合法基础上提出一种揭示内啮合齿轮副延长啮合现象的分析方法。首先采用集中参数法建立风电行星轮系的动力学模型,并求解获得动态啮合力;随后,运用有限元法建立行星轮系内啮合齿轮副的有限元模型,并开展静态接触分析从而获得内啮合齿轮副各啮合位置发生多齿啮合时的变形阈值;最后,将集中参数模型获得的动态啮合力施加在内齿圈有限元模型上计算出内齿圈的动态响应,并结合发生多齿啮合时的变形阈值,从而揭示在不同负载和支撑数量下内齿圈上多齿啮合的分布区域,获得接触应力和齿根应力,分析啮合齿对数量改变前后对应力的影响。结果表明：考虑齿轮柔性后,内啮合齿轮副会出现除理论啮合齿对外其他齿对相接触的现象;随着负载扭矩的增大,内齿圈上三齿啮合首先发生在支撑两侧,随后三齿啮合发生区域不断增加;当行星轮与内齿圈间的啮合由理论两齿啮合变为三齿啮合时,其齿面接触应力和齿根应力小于其在相同时刻只计入两齿啮合时的应力值。     

大型风力机齿轮传动系统机电耦合动态特性研究

针对目前风力机柔性齿轮箱动力学研究时简化电气系统的问题,以某8 MW永磁同步风力机为对象,建立包含详细电气系统和柔性传动链的风力机模型。基于该模型探究电气系统效应对风力机齿轮箱啮合刚度、动态接触应力、振动加速度等动力学特性影响。结果表明：电气系统效应使系统转速、时变啮合刚度、接触应力相位滞后且波动减小;电气系统效应抑制各级齿轮角加速度及箱体振动加速度高频成分并减小传动链振动;风速突变时,电气系统效应可减小高速级齿轮峰值啮合力,增强风力机传动链抵御冲击能力。     

计及齿轮全柔性的风电机组传动链有限元建模及扭振特性分析

大功率风电机组传动链关键部件柔性直接影响机组扭振特性及疲劳寿命,提出考虑齿轮柔性与啮合柔性的传动链有限元建模及扭振特性分析。首先,基于实际双馈风电机组传动链结构、材料属性与几何参数,考虑齿轮箱内齿轮柔性与齿轮啮合柔性,结合叶片、轮毂、主轴和发电机转子,建立风电机组传动链多柔体有限元模型。其次,基于有限元模态分析理论,提出一种基于矢量位移云图筛选扭振频率的分析方法,获取计及齿轮全柔性影响的风电机组中、低频范围的扭振模态,并与不同传动链模型结果进行比较,验证该文所建模型的有效性。最后,分别分析不同齿轮柔性和齿轮啮合柔性对传动链扭振频率和模态的影响。结果表明,该文所建模型不仅能反映传动链扭振固有的低频频率,而且能反映弯扭耦合产生的中频扭振频率,且相比齿轮啮合柔性,齿轮柔性系数影响传动链高频扭振特性明显。     

风电齿轮箱行星轮系的齿面摩擦与齿根裂纹耦合效应计算方法

针对风电增速箱故障率偏高的问题,在对风电机组传动系统的振动响应机理进行分析的基础上,提出一种同时考虑齿根裂纹与齿面摩擦2种因素耦合情况下计算风电增速箱行星轮系动态响应的方法。首先分析考虑不同滑动摩擦因素时,含齿根裂纹缺陷的齿轮其啮合刚度的变化情况;随后运用集中参数法建立一种同时考虑平移和扭转2种力学效应相互影响作用的行星轮系动态响应计算模型。使用该模型在考虑齿根裂纹、齿面滑动摩擦2种因素耦合情况下,对行星轮系时变啮合刚度影响作用进行仿真计算。结果表明,齿面间的滑动摩擦力将导致行星齿轮扭转振动响应在低频区域受到抑制、中频区域得到增强,而齿根裂纹会导致系统出现调制效应且该效应会使行星齿轮的扭转振动频谱响应在行星轮与太阳轮间的啮合频率附近出现调制边频带现象。     

Identification of loading conditions resulting in roller slippage in gearbox bearings of large wind turbines

The dynamic loads on the rollers inside the bearings of large wind turbine gearboxes operating under transient conditions are presented with a focus on identifying conditions leading to slippage of rollers. The methodology was developed using a multi‐body model of the drivetrain coupled with aeroelastic simulations of the wind turbine system. A 5 MW reference wind turbine is considered for which a three‐stage planetary gearbox is designed on the basis of upscaling of an actual 750 kW gearbox unit. Multi‐body dynamic simulations are run using the ADAMS software using a detailed model of the gearbox planetary bearings to investigate transient loads inside the planet bearing. It was found that assembly and pre‐loading conditions have significant influence on the bearing's operation. Also, the load distribution in the gearbox bearings strongly depends on wind turbine operation. Wind turbine start‐up and shut‐down under normal conditions are shown to induce roller slippage, as characterized by loss of contacts and impacts between rollers and raceways. The roller impacts occur under reduced initial pre‐load on opposite sides of the load zone followed by stress variation, which can be one of the potential reasons leading to wear and premature bearing failures. Copyright © 2017 John Wiley & Sons, Ltd.     

混合弹流润滑条件下风电行星直齿轮内啮合动态特性分析

当大型风力发电机在低速重载条件时,齿轮在混合弹流润滑条件下的啮合动态特性难以分析.针对该问题提出齿面接触并联刚度模型,建立行星齿轮啮合动力学模型.基于粗糙峰承载平衡理论,将承载因子理论引入刚度模型中,并与混合弹流润滑理论相结合,可得出计算齿面油膜刚度的新公式,为齿轮混合弹流润滑问题研究提供参考.通过计算结果,可认为在混...     

计入齿形误差的风电机组行星齿轮传动系统动态特性研究

以风电机组行星齿轮传动系统为研究对象,考虑齿形误差因素,建立行星齿轮传动系统平移-扭转动力学分析模型,研究分析各阶次误差对系统动态特性的影响.通过对模型求解,得到不同形式误差下系统动载荷的时域历程和频谱,分析不同形式误差对系统动载荷、太阳轮浮动轨迹以及系统均载性能的影响.研究得出在太阳轮计入齿形误差后,系统动载荷波动以...     

风电机组中两级齿轮传动系统动态温度响应与实验研究

为研究风电机组齿轮传动系统的动态温度场分布特性,以SQI风电机组传动系统实验平台中两级定轴齿轮箱为研究对象,综合考虑齿轮时变啮合刚度和轴承时变刚度对系统影响,采用有限元法并计入轴系柔性建立两级平行轴齿轮箱的齿轮-轴-轴承耦合系统动力学模型.依据传热学原理对热传导,对流换热等参数进行分析,运用有限元法对系统动态温度场进行...     

风电齿轮的微点蚀研究

对影响风电齿轮齿面微点蚀的各相关因素进行了分析,指出为避免发生微点蚀,不仅润滑方面的因素要予以重视,设计与制造因素也同样不能忽略,最后给出了提高齿面抗微点蚀能力可采取的若干技术措施。     

风电机组传动链典型故障特征提取方法

为解决风电机组传动链易发生故障的问题,文章阐述了风电机组齿轮箱特征频率的计算方法和基于振动信号分析的故障特征提取方法。结合实际情况,以行星级齿轮磨损、中间轴小齿轮崩齿、高速轴齿轮崩齿和发电机轴承电腐蚀等典型故障为例,通过齿轮箱特征频率和传动链典型故障振动信号基本特征分析,可较好地完成故障识别。结果表明,采用经典信号处理方法能对上述典型故障进行特征提取,验证了经典方法对单一、明显故障特征提取的有效性,为深入开展传动链故障特征提取方法研究奠定了基础,为风电机组故障检修维护提供了技术支撑。     

Residual signal feature extraction for gearbox planetary stage fault detection

Faults in planetary gears and related bearings, e.g. planet bearings and planet carrier bearings, pose inherent difficulties on their accurate and consistent detection associated mainly to the low energy in slow rotating stages and the operating complexity of planetary gearboxes. In this work, statistical features measuring the signal energy and Gaussianity are calculated from the residual signals between each pair from the first to the fifth tooth mesh frequency of the meshing process in a multi‐stage wind turbine gearbox. The suggested algorithm includes resampling from time to angular domain, identification of the expected spectral signature for proper residual signal calculation and filtering of any frequency component not related to the planetary stage. Two field cases of planet carrier bearing defect and planet wheel spalling are presented and discussed, showing the efficiency of the followed approach and the possibility of characterizing a fault as localized or distributed. Copyright © 2017 John Wiley & Sons, Ltd.     

Fault diagnosis of wind turbine planetary gearbox under nonstationary conditions via adaptive optimal kernel time–frequency analysis

Planetary gearboxes play an important role in wind turbine (WT) drivetrains. WTs usually work under time-varying running conditions due to the volatile wind conditions. The planetary gearbox vibration signals in such an environment are hence highly nonstationary. Conventional spectral analysis and demodulation analysis methods are unable to identify the characteristic frequency of gear fault from such nonstationary signals. As such, this paper presents a time–frequency analysis methods to reveal the constituent frequency components of nonstationary signals and their time-varying features for WT planetary gearbox monitoring. More specifically, we exploit the adaptive optimal kernel (AOK) method for this challenging application because of its fine time–frequency resolution and cross-term free nature, as demonstrated by our simulation analysis. In this study, the AOK method has been applied to identify the time-varying characteristic frequencies of gear fault or to extract different levels of impulses induced by gear faults from lab WT experimental signals and in-situ WT signals under time-varying running conditions. We have demonstrated that the AOK is effective diagnosis of: (a) both the local damage (a single chipped tooth) and distributed faults (wear of all teeth), (b) both sun gear and planet gear faults, and (c) faults with very weak signature (e.g., the sun gear fault at the low speed stage of a WT planetary gearbox).