Study of weather and location effects on wind turbine failure rates

Understanding the availability of wind turbines (WT) is vital to maximize WT energy production and minimize the capital payback period. Previous work on this subject concentrated on reliability and the location of WT failure modes rather than root causes. This paper concentrates on the influence of weather and WT location on failure rate and downtime, to try to understand root causes and the consequences of failure. The paper goes further than a previous study, which used Windstats data from the whole of Denmark, by considering a limited population of identical WTs at three locations on the German Nordzee, Ostzee and in western Germany, using data from WMEP and local weather stations. This new study focuses more precisely than the previous study by using more reliable data. The data were analysed to find the WT failures and weather conditions and then cross‐correlate them. To confirm their representativeness, the reliability characteristics of these smaller WT populations followed the average trends of the overall WMEP survey. However, clear differences were observed in the failure behaviour of the WTs at the three locations. Annual periodicity was seen in the weather data, as expected, but not in individual WT population failure data. However, clear cross‐correlations can be seen between WT failures and weather data, in particular wind speed, maximum temperature and humidity. These cross‐correlations were more convincing than those found in the earlier, larger Danish study, vindicating the more focused approach. It is also clear from the analysis that Operation & Maintenance also has an impact on WT failure rates. These factors will be important for the operation of offshore WTs with the work indicating how weather conditions may affect offshore WT failure rates. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling wind turbine degradation and maintenance

This paper presents an asset model for offshore wind turbine reliability accounting for the degradation, inspection and maintenance processes. The model was developed based on the Petri net method that effectively captures the stochastic nature of the dynamic processes through the use of appropriate statistical distributions. The versatility of the method allows the details of the degradation and maintenance operations to be incorporated in the model. In particular, there are dependent deterioration processes between wind turbine subsystems, complex maintenance rules and the incorporation of condition monitoring systems for early failure indication to enable replacement prior to failure. The purposes of the model are to predict the future condition of wind turbine components and to investigate the effect of a specified maintenance strategy. The model outputs are statistics indicating the performance of the wind turbine components; these include the probability of being in different condition states, the expected number of maintenance actions and the average number and duration of system downtime under any maintenance strategy. Copyright © 2015 John Wiley & Sons, Ltd.     

Offshore wind turbine fault alarm prediction

Offshore wind operations and maintenance (O&M) costs could reach up to one third of the overall project costs. In order to accelerate the deployment of offshore wind farms, costs need to come down. A key contributor to the O&M costs is the component failures and the downtime caused by them. Thus, an understanding is needed on the root cause of these failures. Previous research has indicated the relationship between wind turbine failures and environmental conditions. These studies are using work‐order data from onshore and offshore assets. A limitation of using work orders is that the time of the failure is not known and consequently, the exact environmental conditions cannot be identified. However, if turbine alarms are used to make this correlation, more accurate results can be derived. This paper quantifies this relationship and proposes a novel tool for predicting wind turbine fault alarms for a range of subassemblies, using wind speed statistics. A large variation of the failures between the different subassemblies against the wind speed are shown. The tool uses 5 years of operational data from an offshore wind farm to create a data‐driven predictive model. It is tested under low and high wind conditions, showing very promising results of more than 86% accuracy on seven different scenarios. This study is of interest to wind farm operators seeking to utilize the operational data of their assets to predict future faults, which will allow them to better plan their maintenance activities and have a more efficient spare part management system.     

Application and validation of incrementally complex models for wind turbine aerodynamics,isolated wind turbine in uniform inflow conditions

A comparison of several incrementally complex methods for predicting wind turbine performance, aeroelastic behavior, and wakes is provided. Depending on a wind farm's design, wake interference can cause large power losses and increased turbulence levels within the farm. The goal is to employ modeling methods to reach an improved understanding of wake effects and to use this information to better optimize the layout of new wind farms. A critical decision faced by modelers is the fidelity of the model that is selected to perform simulations. The choice of model fidelity can affect the accuracy, but will also greatly impact the computational time and resource requirements for simulations. To help address this critical question, three modeling methods of varying fidelity have been developed side by side and are compared in this article. The models from low to high complexity are as follows: a blade element‐based method with a free‐vortex wake, an actuator disc‐based method, and a full rotor‐based method. Fluid/structure interfaces are developed for the aerodynamic modeling approaches that allow modeling of discrete blades and are then coupled with a multibody structural dynamics solver in order to perform an aeroelastic analysis. Similar methods have individually been tested by researchers, but we suggest that by developing a suite of models, they can be cross‐compared to grasp the subtleties of each method. The modeling methods are applied to the National Renewable Energy Laboratory Phase VI rotor to predict the turbine aerodynamic and structural loads and then also the wind velocities in the wake. The full rotor method provides the most accurate predictions at the turbine and the use of adaptive mesh refinement to capture the wake to 20 radii downstream is proven particularly successful. Though the full rotor method is unmatched by the lower fidelity methods in stalled conditions and detailed prediction of the downstream wake, there are other less complex conditions where these methods perform as accurately as the full rotor method. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of preventive maintenance intervals on reliability and maintenance costs of wind turbine gearboxes

As many of the installed wind turbines (WTs) get older or approach their design life, there will be a drive to keep extending the lives of the main components especially the gearbox. The challenge of operations and maintenance will potentially be even more as there will be a need to keep the cost to a minimum. Similarly, as years of experience of operating WTs accumulate, knowledge about the behaviour and failure of subsystems is gained as well. Also with good documentation and repository of historical operational, performance and failure data, future decisions of operations and maintenance can be taken on the basis of insights from past experience. This paper presents an approach for implementing preventive maintenance (PM) by using historical failure data to determine the optimal PM interval required to maintain desired reliability of a typical module or subassembly. This paper builds upon previous research in the area of WT gearbox reliability analysis and prediction, taking it further by examining the relationships between the frequency of a PM task and the reliability, availability and maintenance costs. The approach presented demonstrates how historical in‐service failure data can be used in PM task selection based on the minimum maintenance cost and maximum availability. Available historical field failure data of the high speed module of a Vestas 2MW WT gearbox is used to validate the approach and show its practicality. The results of this study are then presented—indicating that choosing the right PM interval based on the minimum unit maintenance cost and maximum availability also improves WT gearbox reliability. Copyright © 2014 John Wiley & Sons, Ltd.     

Adjustment of wind farm power output through flexible turbine operation using wind farm control

When the installed capacity of wind power becomes high, the power generated by wind farms can no longer simply be that dictated by the wind speed. With sufficiently high penetration, it will be necessary for wind farms to provide assistance with supply‐demand matching. The work presented here introduces a wind farm controller that regulates the power generated by the wind farm to match the grid requirements by causing the power generated by each turbine to be adjusted. Further, benefits include fast response to reach the wind farm power demanded, flexibility, little fluctuation in the wind farm power output and provision of synthetic inertia. Copyright © 2015 John Wiley & Sons, Ltd.     

Modelling the aerodynamics of vertical‐axis wind turbines in unsteady wind conditions

Most numerical and experimental studies of the performance of vertical‐axis wind turbines have been conducted with the rotors in steady, and thus somewhat artificial, wind conditions—with the result that turbine aerodynamics, under varying wind conditions, are still poorly understood. The vorticity transport model has been used to investigate the aerodynamic performance and wake dynamics, both in steady and unsteady wind conditions, of three different vertical‐axis wind turbines: one with a straight‐bladed configuration, another with a curved‐bladed configuration and another with a helically twisted configuration. The turbines with non‐twisted blades are shown to be somewhat less efficient than the turbine with helically twisted blades when the rotors are operated at constant rotational speed in unsteady wind conditions. In steady wind conditions, the power coefficients that are produced by both the straight‐bladed and curved‐bladed turbines vary considerably within one rotor revolution because of the continuously varying angle of attack on the blades and, thus, the inherent unsteadiness in the blade aerodynamic loading. These variations are much larger, and thus far more significant, than those that are induced by the unsteadiness in the wind conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

离网型风力发电机的大风限速保护研究

如果解决不好离网型风力发电机的大风限速保护问题,就会大大地降低其可靠性和安全性.文章从风轮与发电机的匹配人手,一改传统离网型风力发电机最佳功率匹配运行为峰前匹配运行,使风力发电机在大风时保持较低的风能利用系数,具有大风时的限速保护作用.     

Dependence of optimal wind turbine spacing on wind farm length

Recent large eddy simulations have led to improved parameterizations of the effective roughness height of wind farms. This effective roughness height can be used to predict the wind velocity at hub‐height as function of the geometric mean of the spanwise and streamwise turbine spacings and the turbine loading factors. Recently, Meyers and Meneveau used these parameterizations to make predictions for the optimal wind turbine spacing in infinitely large wind farms. They found that for a realistic cost ratio between the turbines and the used land surface, the optimal turbine spacing may be considerably larger than that used in conventional wind farms. Here, we extend this analysis by taking the length of the wind farm, i.e. the number of rows in the downstream direction into account and show that the optimal turbine spacing strongly depends on the wind farm length. For small to moderately sized wind farms, the model predictions are consistent with spacings found in operational wind farms. For much larger wind farms, the extended optimal spacing found for infinite wind farms is confirmed. Copyright © 2015 John Wiley & Sons, Ltd.     

兆瓦风力发电机系统可靠性设计理论研究

在分析兆瓦风力发电机系统的基础上,提出了兆瓦风力发电机发电系统可靠度的基本概念及计算方法,建立了可靠度最优分配的数学模型及最优兆瓦风机发电系统可靠性设计的数学模型。     

Reliability comparison of direct‐drive and geared‐drive wind turbine concepts

This paper proposes for wind turbines (WTs) an analytical reliability method, used on other engineering systems, to compare the reliability of different turbine concepts. The main focus of the paper is to compare the reliability of geared generator and direct‐drive concept WTs. Modification methods are also recommended for improving the availability of WTs and geared generator concept incorporating doubly fed induction generator. Copyright © 2009 John Wiley & Sons, Ltd.     

风力机叶片动态气弹变形及其对整机性能的影响

基于风力机整机刚柔耦合模型,文章提出了一种叶片动态气弹扭转变形分析的新方法。该方法采用SIMPACK和AeroDyn软件联合数值仿真对风力机在几种恶劣风况下进行动力学分析,通过对分析结果的变换处理,进而得到叶片在复杂工况下的动态气弹变形数据。采用该方法,重点分析了叶片气弹扭转变形对风力机气动功率及气弹稳定性的影响。该方法为大型风电叶片的气弹特性评价以及气弹剪裁设计提供了一种新的技术手段。     

风特性对风力发电机组输出功率的影响

为了准确研究不同类型的风速对并网风电机组输出功率的影响,建立了并网风力发电机模型和不同类型风速的模型。在不同类型风速的扰动下,对异步风电机输出功率的波动进行了仿真分析;针对引起功率振荡最严重的阵风,进行了不同频率的阵风扰动下风电机组功率振荡的比较,对阵风扰动下风电机组间的相互影响进行了仿真分析。结果表明,在相同幅值的扰动下,阵风引起的风电机组功率振荡最严重,机组功率振荡情况与阵风扰动的频率有关,单台机组在阵风扰动下产生的振荡对其他机组也会产生一定的影响。     

风电场风电机组的接地设计

较系统地介绍了风电场风电机组对接地电阻的要求、接地设计思路及方法,并提供实际工程中接地网布置图实例作为参考。     

Collapse analysis of wind turbine tower under the coupled effects of wind and near‐field earthquake

In this paper, the pattern of wind turbine tower collapse as a result of the coupled effects of wind and an intense, near‐field earthquake is investigated. The constitutive relation of the tower cylinder steel is simulated via a nonlinear kinematic hardening model, and the specific value of each parameter in the constitutive model is provided. A precise model of the tower structure coupled with the blade is created using a nonlinear, finite element method. This method is compared with the results from a static pushover test of a small cylindrical tower to validate the finite element modeling method in this research. Two earthquake wave sets are selected as inputs. One contains 20 near‐field velocity pulse‐like ground motion waves with various pulse periods; the other contains 20 ordinary far‐field ground motion waves. A wind turbine tower with a hub height of 60 m is selected as an example for analysis. The dynamic response of this tower as a result of the coupled effects of the two ground motion wave sets and a transient wind load is calculated using nonlinear time‐history analysis. The calculation results shows that the average horizontal displacement of the tower top as a result of the near‐field velocity pulse‐like ground motion is 33% larger than the case with far‐field ground motion. Finally, the seismic collapse vulnerability curve of this wind turbine tower is calculated. The seismic collapse capacity of the tower is evaluated, and the seismic collapse pattern of the tower is analyzed.     

特种风力发电机组塔筒防腐方案研究

高原和海洋的风能资源丰富,更能发挥大容量风力发电机组的优势,利用前景广阔。但高原和海上的自然环境恶劣,对风机承载部件——塔筒的防腐要求更为严格。针对在高原和海上运行的特种风机,分析了塔筒的腐蚀环境,研究了塔筒的防腐原理,提出了塔筒的具体防腐措施和防腐方案,为特种风机塔筒的防腐提供了参考。     

Modelling and analysis of floating spar‐type wind turbine drivetrain

This paper studies the drivetrain dynamics of a 750 kW spar‐type floating wind turbine (FWT). The drivetrain studied is a high‐speed generator, one‐stage planetary, two‐stage parallel and three‐point support type. The response analysis is carried out in two steps. First, global aero‐hydro‐elastic‐servo time‐domain analyses are performed using HAWC2. The main shaft loads, which include the axial forces, shear forces and bending moments, are obtained in this integrated wind–wave response analysis. These loads are then used as inputs for the multi‐body drivetrain time‐domain analyses in SIMPACK. The investigations are largely based on comparisons of the main shaft loads and internal drivetrain responses from 1 h simulations. The tooth contact forces, bearing loads and gear deflections are the internal drivetrain response variables studied. The comparisons are based on the mean values, standard deviations and maximum values extrapolated using a 10 ^{? 5} up‐crossing rate. Both operational and parked conditions are considered. The investigation consists of three parts. First, the responses are compared between the FWT and its equivalent land‐based version. Second, the contributions from the main shaft loads (shear forces, axial forces and bending moments) and nacelle motions are investigated individually. Third, an improved four‐point support (4PT) system is studied and compared against the original three‐point support system for the FWT. The results show that there are general increases in the standard deviations of the main shaft loads and internal drivetrain responses in the FWT. In addition, these increases are a result of the increased main shaft loads in the FWT, especially the non‐torque loads. Last, the 4PT system, when applied to a FWT drivetrain, significantly reduces the tooth contact forces and bearing loads in the low‐speed stage, but this result comes at the expense of increased main bearing radial loads. Copyright © 2013 John Wiley & Sons, Ltd.     

Impact of low‐level wind maxima below hub height on wind turbine sound propagation

An analysis of the effect of low‐level wind maxima (LLWM) below hub height on sound propagating from wind turbines has been performed at a site in northern Sweden. The stably stratified boundary layer, which is typical for cold climates, commonly features LLWM. The simplified concept for the effects of refraction, based on the logarithmic wind profile or other approaches where the wind speed is continuously increasing with height, is often not applicable there. Long‐term meteorological measurements in the vicinity of a wind farm were therefore used to identify LLWM. Sound measurements were conducted simultaneously to the meteorological measurements. LLWM below hub height decrease the sound level close to the surface downwind of the wind farm. This effect increases with increasing strength of the LLWM. The occurrence of LLWM as well as strength and height of the LLWM are dependent on the wind direction.     

Characterizing the response of a wind turbine model under complex inflow conditions

A horizontal axis wind turbine model was tested in a closed‐circuit wind tunnel under various inflow conditions. Separate experiments placed the test turbine (i) in the wake of a three‐dimensional, sinusoidal hill, (ii) in the wake of another turbine and (iii) in the turbulent boundary layer, as a reference case. Simultaneous high‐frequency measurements of the turbine output voltage, rotor angular velocity along with streamwise and wall normal velocity components were collected at various locations through the turbine's miniature direct‐current (DC) generator, a high‐resolution laser tachometer and cross‐wire anemometer, respectively. Validation trials were conducted first in order to characterize the test turbine's output and response to the baseline turbulent boundary layer. Analysis was performed by comparing the cross‐wire anemometry measurements of the incoming flow with the turbine voltage output to investigate the unsteady rotor kinematics under different flow perturbations. Using spectral, auto‐correlation and cross‐correlation methods, it was found that the flow structures developing downwind of the hill leave a stronger signature on the fluctuations and spectrum of the rotor angular velocity, as compared with those flow structures filtered or deflected by placing a turbine upwind. In summary, we show that the effects on downwind turbines of complex terrain and multi‐turbine arrangements are consistent with the induced modifications by the hill or turbine on the large scale structures in the incoming flow. Copyright © 2014 John Wiley & Sons, Ltd.