Wind turbine reliability data review and impacts on levelised cost of energy

Reliability is critical to the design, operation, maintenance, and performance assessment and improvement of wind turbines (WTs). This paper systematically reviews publicly available reliability data for both onshore and offshore WTs and investigates the impacts of reliability on the cost of energy. WT failure rates and downtimes, broken down by subassembly, are collated from 18 publicly available databases including over 18 000 WTs, corresponding to over 90 000 turbine‐years. The data are classified based on the types of data collected (failure rate and stop rate) and by onshore and offshore populations. A comprehensive analysis is performed to investigate WT subassembly reliability data variations, identify critical subassemblies, compare onshore and offshore WT reliability, and understand possible sources of uncertainty. Large variations in both failure rates and downtimes are observed, and the skew in failure rate distribution implies that large databases with low failure rates, despite their diverse populations, are less uncertain than more targeted surveys, which are easily skewed by WT type failures. A model is presented to evaluate the levelised cost of energy as a function of WT failure rates and downtimes. A numerical study proves a strong and nonlinear relationship between WT reliability and operation and maintenance expenditure as well as annual energy production. Together with the cost analysis model, the findings can help WT operators identify the optimal degree of reliability improvement to minimise the levelised cost of energy.     

Review of recent offshore wind power developments in china

Rapid wind power development in China has attracted worldwide attention. The huge market potential and fast development of wind turbine manufacturing capacity are making China a world leader in wind power development. In 2010, with the newly installed wind power capacity and the cumulative installed capacity, China was ranked first in the world. In 2009, China also constructed and commissioned its first large offshore wind farm near Shanghai. Following earlier papers reviewing the state of China's onshore wind industry, this paper presents a broader perspective and up‐to‐date survey of China's offshore wind power development, making comparisons between the developments in the rest of the world and China, to draw out similarities and differences and lessons for the China offshore wind industry. The paper highlights six important aspects for China's offshore wind development: economics, location, Grid connection, technological development, environmental adaptation and national policies. The authors make recommendations for mitigating some outstanding issues in these six aspects for the future development of China's offshore wind resource. Copyright © 2012 John Wiley & Sons, Ltd.     

Failure rate,repair time and unscheduled O&M cost analysis of offshore wind turbines

Determining and understanding offshore wind turbine failure rates and resource requirement for repair are vital for modelling and reducing O&M costs and in turn reducing the cost of energy. While few offshore failure rates have been published in the past even less details on resource requirement for repair exist in the public domain. Based on ~350 offshore wind turbines throughout Europe this paper provides failure rates for the overall wind turbine and its sub‐assemblies. It also provides failure rates by year of operation, cost category and failure modes for the components/sub‐assemblies that are the highest contributor to the overall failure rate. Repair times, average repair costs and average number of technicians required for repair are also detailed in this paper. An onshore to offshore failure rate comparison is carried out for generators and converters based on this analysis and an analysis carried out in a past publication. The results of this paper will contribute to offshore wind O&M cost and resource modelling and aid in better decision making for O&M planners and managers. Copyright © 2015 John Wiley & Sons, Ltd.     

Wind turbine SCADA alarm analysis for improving reliability

Previous research for detecting incipient wind turbine failures, using condition monitoring algorithms, concentrated on wind turbine Supervisory Control and Data Acquisition (SCADA) signals, such as power output, wind speed and bearing temperatures, using power‐curve and temperature relationships. However, very little research effort has been made on wind turbine SCADA alarms. When wind turbines are operating in significantly sized wind farms, these alarm triggers are overwhelming for operators or maintainers alike because of large number occurring in a 10 min SCADA period. This paper considers these alarms originating in two large populations of modern onshore wind turbines over a period of 1–2 years. First, an analysis is made on where the alarms originate. Second, a methodology for prioritizing the alarms is adopted from an oil and gas industry standard to show the seriousness of the alarm data volume. Third, two methods of alarm analysis, time‐sequence and probability‐based, are proposed and demonstrated on the data from one of the wind turbine populations, considering pitch and converter systems with known faults. The results of this work show that alarm data require relatively little storage yet provide rich condition monitoring information. Both the time‐sequence and probability‐based analysis methods have the potential to rationalize and reduce alarm data, providing valuable fault detection, diagnosis and prognosis from the conditions under which the alarms are generated. These methods should be developed and integrated into an intelligent alarm handling system for wind farms, aimed at improving wind turbine reliability to reduce downtime, increase availability and leading to a well‐organized maintenance schedule. Copyright © 2011 John Wiley & Sons, Ltd.     

Reliability of onshore wind turbines based on linking power curves to failure and maintenance records: A case study in central Spain

Wind turbine (WT) reliability has come to the forefront of research due to the rapid growth of wind energy in recent years. Reliability information can help understand failure causes and focus maintenance and prevention efforts on the most critical components, reducing costs and increasing profits. This paper offers new insights into WT reliability after analysing the data provided by the Supervisory Control And Data Acquisition (SCADA) system collected from seven onshore WTs located in central Spain from January 2014 to September 2021. To this end, we propose a method to link SCADA data to failure and maintenance records based on checking whether each 10-min average time sample was collected when any failure or maintenance action had been reported. These records have been manually mapped to the WT taxonomy based on the standard Reference Designation System for Power Plants (RDS-PP®) with minor changes. We present three different results: (i) The capacity factor and time-based availability of each WT; (ii) the subsystem failure rate and downtime to identify the most critical ones; and (iii) each WT power curve with the 10-min time samples labelled as healthy, under maintenance, or failure states, along with a ranking of the subsystems causing the most failures in each part of the power curves. It is the first time that time samples are linked to failure and maintenance records to visualise their distribution on the power curves. These results can help research point in the right direction to improve reliability and increase electricity production worldwide.     

Wind turbine fatigue loads as a function of atmospheric conditions offshore

In recent years, there has been a growing interest by the wind energy community to assess the impact of atmospheric stability on wind turbine performance; however, up to now, typically, stability is considered in several distinct arbitrary stability classes. As a consequence, each stability class considered still covers a wide range of conditions. In this paper, wind turbine fatigue loads are studied as a function of atmospheric stability without a classification system, and instead, atmospheric conditions are described by a continuous joint probability distribution of wind speed and stability. Simulated fatigue loads based upon this joint probability distribution have been compared with two distinct different cases, one in which seven stability classes are adopted and one neglecting atmospheric stability by following International Electrotechnical Commission (IEC) standards. It is found that for the offshore site considered in this study, fatigue loads of the blade root, rotor and tower loads significantly increase if one follows the IEC standards (by up to 28% for the tower loads) and decrease if one considers several stability classes (by up to 13% for the tower loads). The substantial decrease found for the specific stability classes can be limited by considering one stability class that coincides with the mean stability of a given hub height wind speed. The difference in simulated fatigue loads by adopting distinct stability classes is primarily caused by neglecting strong unstable conditions for which relatively high fatigue loads occur. Combined, it is found that one has to carefully consider all stability conditions in wind turbine fatigue load simulations. Copyright © 2016 John Wiley & Sons, Ltd.     

顺应新潮流 把握新趋势简

Mean wind force coefficients of nacelles are investigated by a wind tunnel test and are compared with those in current codes, such as the Germanischer Lloyd Guideline 2010 (GL2010) and Eurocode, in order to clarify the effects of the ground, presence of a hub, turbulence in the incident flow and nacelle length on these coefficients. Formulas for the mean wind force coefficients are proposed as a function of yaw angles. It is found that mean wind force coefficients of wind turbine nacelles specified in GL2010 are underestimated in comparison with those obtained by wind tunnel tests. Pressure measurements of a nacelle are also conducted. Notably, the mean pressure coefficients for design load case 6.2 (DLC6.2) are significantly larger than those for design load case 6.1 (DLC6.1) in IEC61400‐1. Maximum and minimum mean pressure coefficients are proposed for the DLC6.1 and DLC6.2 by the wind tunnel test, which are similar to those in Eurocode and are larger than those proposed in GL2010. Copyright © 2012 John Wiley & Sons, Ltd.     

Soil–structure reliability of offshore wind turbine monopile foundations

An overview of offshore wind turbine (OWT) foundations is presented, focusing primarily on the monopile foundation. The uncertainty in offshore soil conditions as well as random wind and wave loading is currently treated with a deterministic design procedure, though some standards allow engineers to use a probability‐based approach. Laterally loaded monopile foundations are typically designed using the American Petroleum Institute p‐y method, which is problematic for large OWT pile diameters. Probabilistic methods are used to examine the reliability of OWT pile foundations under serviceability limit states using Euler–Bernoulli beam elements in a two‐dimensional pile–spring model, non‐linear with respect to the soil springs. The effects of soil property variation, pile design parameters, loading and large diameters on OWT pile reliability are presented. Copyright © 2014 John Wiley & Sons, Ltd.     

两种常用漂浮式风力机平台动态特性分析

分别针对MIT/NREL TLP和Umaine-Hywind Spar两种海上风力机浮式平台主体的水动力特性进行研究,旨在分析两者的系泊稳定性.基于海洋水动力学和结构动力学理论,建立了平台/缆索系统耦合模型,在水深和外界载荷激励相同的情况下,利用有限元分析ANSYS软件中的水动力学计算模块进行时域、频域响应分析,研究了两种平台在海风、海流和随机波联合作用下的动态响应,并分析了两种平台随波浪频率的响应变化.结果表明:MIT/NREL TLP平台的动态响应较大,而Umaine-Hywind Spar平台动态响应较小;两平台均在低频波浪作用下产生响应峰值.     

A new turbulence model for offshore wind turbine standards

Correct turbulence intensity modeling is crucial for fatigue load estimation for wind turbine structural design. It is well known that the International Electrotechnical Commission 61400‐3 Normal Turbulence Model recommended for offshore wind turbine design is not representative of offshore wind conditions. A new model is urgently needed as offshore wind energy is rapidly developing worldwide. After evaluating the suitability of the Normal Turbulence Model at three sites in Asia, Europe and the USA, it is found that wind–wave interaction and stability correction should be taken into account in modeling the offshore turbulence intensity and wind speed relationship. Therefore, a new turbulence intensity model, which models wind–wave interaction with the Charnock equation and adjusts for the influence of atmospheric stability through empirical turbulence scaling functions for the unstable atmospheric boundary layer, was developed. The new model is physically based and is tested against observations from the three sites. It shows better performance than the Normal Turbulence Model and hence is recommended to replace the Normal Turbulence Model. For model application, only two parameters are required, which are defined herein to represent offshore sites with high, medium and low turbulence intensities. Copyright © 2013 John Wiley & Sons, Ltd.     

不同入射角风波流海上漂浮式风力机频域与时域动态特性

采用边界元并结合多体动力学方法分析了张力腿平台(TLP)漂浮式风力机结构,研究了平台结构在不同方向上的频域与时域运动响应变化,并比较了漂浮式平台在海洋环境条件下风波流联合作用时和波浪载荷独立作用时的运动响应,得到了平台结构在时域中的动力响应.研究结果表明:漂浮式平台在频域变化范围内,运动响应主要集中在低频部分,绕射力对漂浮式海上风力机TLP的作用力不能忽略;风波流联合作用时的运动响应标准差大于波浪载荷独立作用时的运动响应标准差,且平台偏离平衡位置的程度更加剧烈;平均运动响应及标准差在入射角分别为0°、22.5°和45°时相差微小.研究结果对海上张力腿平台结构设计与优化具有很高的参考价值.     

Reliability assessment for Chinese domestic wind turbines based on data mining techniques

In this work, based on the field operating data of a Chinese domestic wind farm, which came from the supervisory control and data acquisition system, data mining techniques are applied to analyze the reliability characteristics of wind turbines and their components. The reliability indexes including time among failures, failure rate, and downtime are analyzed. On that basis, the key components that influence the wind turbines' reliability most seriously are determined. The internal relation between the failure rate and the environmental temperature is identified with correlation function, and time series approach is used to analyze the seasonal feature of the wind turbines' failure rate. The results show that compared with the wind turbines mentioned in the literatures, the failure rate of the current sample is higher. Among the components, the failure rates of electrical and control systems are the highest, while the corresponding repair time is relatively short; on the contrary, the failure rates of main shaft, gearbox, and generator are relatively low, while the average time for maintenance is comparably long. Furthermore, there is an obvious dependency between the failure rate and environmental temperature, and the failure rate has a clear seasonal feature.     

Effective turbulence and its implications in wind turbine fatigue assessment

The effective turbulence approximation is widely used in the wind energy industry for site‐specific fatigue assessment of wind turbines with reference to loads. It significantly reduces the amount of aero‐elastic simulations required to document structural integrity by integrating out the directional variation of turbulence. Deriving the effective turbulence involves assumptions related to load effect histories, structural dynamics, and material fatigue strength. These assumptions may lead to low accuracy of fatigue load assessments by the effective turbulence compared with full directional simulations. This paper quantifies the implications of the effective turbulence for a multimegawatt wind turbine during normal operation. Analyses based on wind measurements from almost one hundred international sites document that the effective turbulence provides accurate results compared with full sector‐wise simulations, but only when linear SN ‐curves are assumed. For a more advanced steel tower design approach using a bilinear SN ‐curve, a reduction of the cross‐sectional design parameters by almost 10% is achieved. Additional 10% reduction can be obtained if fatigue damage is estimated utilizing the wind direction information. By applying a probabilistic approach, it is shown that this reduction in the design parameter of the steel tower does not compromise the structural integrity when the current IEC 61400‐1 standard is followed. The results presented may improve decision making in site‐specific fatigue assessments of wind turbines and prevent overconservative design, which results from the use of the effective turbulence, and thereby reduce the cost of wind energy.     

Evaluating the importance of mooring line model fidelity in floating offshore wind turbine simulations

Accurate computer modelling is critical in achieving cost‐effective floating offshore wind turbine designs. Although a range of modelling fidelities are available for all parts of the simulation, a lower‐fidelity quasi‐static approach that neglects inertia and hydrodynamics is often used for the mooring line model. The loss of accuracy from using this approach has not been thoroughly studied across different support structure designs. To test the adequacy of this widely used simplified mooring line modelling approach, the floating wind turbine simulator FAST (National Renewable Energy Laboratory, Golden, Colorado) was modified to allow the use of a high‐fidelity dynamic mooring line model, ProteusDS (Dynamic Systems Analysis Inc. of Victoria, BC, Canada). Three standard floating wind turbine designs were implemented in this new simulator arrangement and tested using a set of steady and stochastic wind and wave conditions. The static equivalence between the built‐in quasi‐static mooring model and the dynamic mooring model is within 0.6% in terms of fairlead tension. Tests of the systems’ responses in still water indicate that the hydrodynamic damping of the mooring lines can constitute anywhere from 1% to 35% of the overall system damping in pitch, depending on the design. Tests in steady and stochastic operating conditions show that for very stable designs with slack moorings, or designs with taut moorings, a quasi‐static mooring model can in many conditions predict the platform motions and turbine loads with reasonable accuracy. For slack‐moored designs with larger platform motions, however, a quasi‐static model can lead to inaccuracies of as much as 30% in the damage‐equivalent and extreme loads on the turbine. An important observation is that even in situations where the platform response is predicted reasonably well by a quasi‐static model, larger inaccuracies can arise in the response of the rotor blades. These inaccuracies are more severe in the time series (with instantaneous discrepancies as high as 50% of the mean load) than in the corresponding damage‐equivalent and extreme loads calculated over multiple stochastic simulations. Consequently, differences in damage‐equivalent and extreme load metrics should be considered a floor to the measure of inaccuracy caused by a quasi‐static mooring model. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Feasibility study of offshore wind turbine substructures for southwest offshore wind farm project in Korea

Korea has huge potential for offshore wind energy and the first Korean offshore wind farm has been initiated off the southwest coast. With increasing water depth, different substructures of the offshore wind turbine, such as the jacket and multipile, are the increasing focus of attention because they appear to be cost-effective. However, these substructures are still in the early stages of development in the offshore wind industry. The aim of the present study was to design a suitable substructure, such as a jacket or multipile, to support a 5 MW wind turbine in 33 m deep water for the Korean Southwest Offshore Wind Farm. This study also aimed to compare the dynamic responses of different substructures including the monopile, jacket and multipile and evaluate their feasibility. We therefore performed an eigenanalysis and a coupled aero-hydro-servo-elastic simulation under deterministic and stochastic conditions in the environmental conditions in Korea. The results showed that the designed jacket and multipile substructures, together with the modified monopile, were well located at soft–stiff intervals, where most modern utility-scale wind turbine support structures are designed. The dynamic responses of the different substructures showed that of the three substructures, the performance of the jacket was very good. In addition, considering the simple configuration of the multipile, which results in lower manufacturing cost, this substructure can provide another possible solution for Korean’s first offshore wind farm. This study provides knowledge that can be applied for the deployment of large-scale offshore wind turbines in intermediate water depths in Korea.     

Wind turbine sensor array for monitoring avian and bat collisions

Assessment of avian and bat collisions with wind turbines is necessary to ensure that the benefits of renewable wind power generation are not outweighed by mortality of protected species. An onboard, integrated multisensor system capable of providing detection of turbine collision events, including taxonomic information, was developed. The conceptual design of a multisensor system including a vibration sensing node, an optics node, and an bioacoustic node with an event‐driven trigger architecture was field‐tested on utility‐scale wind turbines. A pixel density computational model was built to estimate the spatial coverage and target resolution to the optimized configuration for camera placement. Field test results of the vibration node showed that nearly half of the recorded impact events were successfully identified by visual inspection and running short‐time Fourier transform on recorded vibration signals. The remaining undetected impact events were masked under background noise due to low impact energy and high background noise of the operating turbine, which result in subsequent low signal‐to‐noise ratio. Our results demonstrate the feasibility of triggering the system through single impact event sensed by vibration sensors.     

Numerical study of a concept for major repair and replacement of offshore wind turbine blades

Repair and replacement of offshore wind turbine blades are necessary for current and future offshore wind turbines. To date, repair activities are often conducted using huge jack‐up crane vessels and by applying a reverse installation procedure. Because of the high costs associated with installation and removal of offshore wind turbine components and the low profit margin of the offshore wind industry, alternative methods for installation and removal are needed. This paper introduces a novel concept for replacement or installation of offshore wind turbine blades. The concept involves a medium‐sized jack‐up crane vessel and a tower climbing mechanism. This mechanism provides a stable platform for clamping, lowering, and lifting of a blade. A case study of a 5‐MW offshore wind turbine is shown, where common engineering practices were applied and numerical simulations of the marine operations were carried out using finite element and multibody simulation tools. Operational limits for wave and wind actions were established to demonstrate the technical feasibility of the proposed concept.     

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。     

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。