Estimation of lightning current amplitudes incident to wind turbines in exposed locations

This paper proposes a novel and comprehensive methodology for estimation of lightning current amplitudes, which are incident to wind turbines (WT) at lightning‐exposed locations, i.e., hilltops. The proposed methodology takes into the account the following aspects related to WT lightning incidence: (i) site topology and keraunic level, (ii)statistical nature of lightning currents, (iii) WT effective height, (iv) dependence of lightning current amplitudes on the WT effective height, (v) influence of an upward‐initiated connecting streamers interaction with a downward‐propagating step leader on the WT lightning attractiveness, and (vi) both downward and upward lightning strikes and their relative contribution in relation to the WT effective height. This methodology could be perceived as beneficial in providing relevant lightning‐current amplitudes—particularly at lightning‐endangered locations and wind farm sites characterized by high soil resistivity—for wind turbine and wind farm overvoltage protection and backsurge studies, as well as the WT grounding systems transient analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Protection of wind energy systems against the indirect effects of lightning

This paper is concerned with the protection of wind energy systems against the indirect effects of lightning. As wind energy is gaining increasing importance throughout the world, lightning damages involving wind energy systems have come to be regarded with more attention. Nevertheless, there are still very few studies in Portugal regarding lightning protection of wind energy systems using models of the Electro-Magnetic Transients Program (EMTP). Hence, a new case study is presented in this paper, based on a wind turbine with an interconnecting transformer, considering that lightning strikes the soil near the tower at a distance such that galvanic coupling occurs through the grounding electrode. Computer simulations obtained by using EMTP-RV are presented and conclusions are duly drawn.     

Assessment of lightning current parameters suitable for wind turbine overvoltage protection analysis

A selection procedure for determining the lightning current parameters, suitable for wind turbine overvoltage protection analysis, will be presented in this paper. It will be based on the mathematical model that accounts for the wind turbine geometry, keraunic level, statistical distribution of lightning current parameters and correlation between statistical variables defining lightning current waveshape. Theoretical analysis will be backed up by the most recent propositions of parameters that define statistical distributions and thereafter applied on the concrete wind turbine example. Subsequently, obtained results would provide insight into the selection procedure for the lightning current parameters (i.e., amplitude, front duration, wave duration and polarity), associated with lightning stroke incidence to wind turbines. Emphases will be given to the modern new‐generation wind turbines. This selection procedure could be subsequently applied in the analysis (and design) of the wind turbine and wind farm overvoltage protection, with emphasis on the so‐called back‐surge phenomenon. Copyright © 2011 John Wiley & Sons, Ltd.     

Wind farm grounding system design for transient currents

Wind turbines are often very high structures that are usually installed in high keraunic level areas. The keraunic level is the number of storm days per year. Therefore, wind farms are very vulnerable to lightning discharge. The damage due to a lightning strike can be reduced if the high current is quickly conducted to the ground.To date, wind turbine grounding system designs have been based on prior experience, without accurately studying transient grounding system behavior.In this work, typical wind farm grounding system geometries are analyzed in the context of lightning strikes.     

风电场防雷接地系统的施工工艺分析

雷击事故在风电场中时有发生,为避免雷击事故中冲击电流对风力机的损害,风力机的防雷接地系统至关重要。文中结合大唐长清风电场一期工程采取的防雷接地系统方法,对风电场降防雷接地系统的施工工艺进行阐述,通过对施工工艺的分析及接地电阻阻值的测量,得出风场中各风机的接地电阻介于2．95—3．69Ω之间,说明采用多种降阻措施相结合的方法能有效的起到降低电阻的作用,同时也证明该风电场的防雷接地系统施工工艺是满足设计要求的。     

500 kV海底电缆雷电过电压研究

依托南方主网与海南电网联网工程,运用ATP-EMTP电磁暂态分析软件,建立了500 kV架空线路与海底电缆线路的雷电侵入波仿真计算模型,采用修正后的电气几何模型法来计算最大绕击雷电流,采用先导发展法作为绝缘子串和空气间隙放电闪络判据,计算架空线路遭受绕击和反击时,无避雷器和有避雷器2种情况下海底电缆主绝缘上所承受的雷电过电压,据此校核海底电缆雷电冲击绝缘水平及避雷器配置的合理性。研究结果表明,合理配置避雷器大大降低了雷电过电压对海缆的影响,在架空线路遭受绕击和-250 kA雷电流反击时,海底电缆最大雷电过电压分别为-916 kV和-923 kV,海底电缆绝缘裕度和避雷器配置满足防雷要求。     

Reliable and lightning‐safe monitoring of wind turbine rotor blades using optically powered sensors

Blade condition monitoring systems with fiber‐optic sensors attract much attention because they are resistant to lightning strikes, a major issue with increasing blade lengths. However, fiber‐optic sensor systems are more complex and more expensive than their electronic counterparts. We describe a new blade condition monitoring system, which combines the lightning safety of optical fibers with the reliability and cost‐effectiveness of electronic sensors. The optical fibers transport data from the blades to the hub, and in addition, they provide the electrical power for operating the sensor units in the blades. To achieve full protection against lightning‐induced electromagnetic fields, an appropriate shielding of the sensor units is required. We present results on the reliability of a newly developed prototype based on optically powered sensors. In a field trial, the unit monitored successfully the blade vibrations of a 1.5 MW wind turbine for a period of 23 months. Copyright © 2016 John Wiley & Sons, Ltd.     

海上风电场海底高压电缆电磁暂态过程的仿真分析

为了能更好地确定海上风电场海底高压电缆的选型要求,使用PSCAD／EMTDC软件建立相应的海上风电场仿真计算模型。针对海上风电场工频过电压、操作过电压和雷电过电压这3种电磁暂态过程的不同特点,进行仿真,并且考虑了不同的系统条件下上述3种过电压对电缆绝缘的影响。在操作过电压中,重点研究了合闸电阻对过电压的影响;而在雷电过电压中重点研究的是架空线路受雷电侵入波的过电压。仿真结果表明,海底电缆各层的结构参数对海底电缆的电磁暂态有着不同程度的影响,其中导体层、绝缘层、HDPE层对海底电缆的电磁暂态影响尤为明显。另外,海底高压电缆的护套层材料和主绝缘层材料也对电磁暂态有影响。     

A new method for spatial allocation of turbines in a wind farm based on lightning protection efficiency

Existing studies of the spatial allocation of wind farms are typically based on turbine power generation efficiency and rarely consider the damage caused by lightning strikes. However, lightning damage seriously affects the economic performance of wind farms because of the high cost of repairing or replacing damaged blades. This paper proposes a method for the spatial optimization of multiple turbines based on lightning protection dependability. Firstly, the lightning protection efficiency of turbine blade protection systems is analyzed by combining the physical mechanisms of lightning leader progression with a conventional electro‐geometric model to develop an electro‐geometric model of turbine blades (EGMTB). Then, the optimized spatial allocation of multiple turbines in a wind farm is investigated using the EGMTB. The results are illustrated from an example wind farm with 1.5 MW turbines, which shows that the optimal spacing between two turbines perpendicular to the prevailing wind direction L_⊥ is 4R‐6R, where R is the length of a turbine blade. This spacing is shown to effectively shield turbine blades from lightning damage over a wide range of lightning currents (>26‐60 kA). Note that, the suggested L_⊥ will be smaller considering the influence of lightning polarity as it takes more difficulty developing upward leader (UL) in the condition of positive lightning striking. Experiments verify the effectiveness and correctness of this method.     

Calculation of electromagnetic induction inside a wind turbine tower struck by lightning

An efficient algorithm is described in this paper for calculating the magnetic transient effects in a wind turbine tower struck by lightning. An electrical network model of the tower is established to compute the transient responses on its surface, and the electrical parameters of the network are determined considering the effect of ground. Based on the transient current responses along the tower conductors, the evaluation of magnetic field distribution is presented directly in time domain, and the transient overvoltage induced in a loop is also calculated according to the law of electromagnetic induction. The results are helpful in determining possible hazards and designing lightning protection systems. © 2009 John Wiley & Sons, Ltd.     

A CFD study into the influence of unsteady aerodynamic interference on wind turbine surge motion

To improve knowledge of the unsteady aerodynamic characteristics and interference effects of a floating offshore wind turbine (FOWT), this article focuses on the platform surge motion of a full configuration wind turbine with the rotating blades, hub, nacelle, and tower shapes. Unsteady aerodynamic analyses considering the moving motion of an entire configuration wind turbine have been conducted using an advanced computational fluid dynamics (CFD) and a conventional blade element momentum (BEM) analyses. The present CFD simulation is based on an advanced overset moving grid method to accurately consider the local and global motion of a three-dimensional wind turbine. The effects of various oscillation frequencies and amplitudes of the platform surge motion have been widely investigated herein. Three-dimensional unsteady flow fields around the moving wind turbine with rotating blades are graphically presented in detail. Complex flow interactions among blade tip vortices, tower shedding vortices, and turbulent wakes are physically observed. Comparisons of different aerodynamic analyses under the periodic surge motions are summarized to show the potential distinction among applied numerical methods. The present result indicates that the unsteady aerodynamic thrust and power tend to vary considerably depending on the oscillation frequency and amplitude of the surge motion.     

220kV海上风电场混合输电线路工频过电压研究

工频过电压是影响220kV海上风电场混合海缆输电线路安全的重要因素。以我国东部某典型的220kV近海风电场输电系统为例,基于ATP-EMTP对海上风电场系统及其送出的混合海缆输电线路进行建模,对混合线路的空载长线电容效应工频过电压进行了理论分析,分别仿真计算了不同海缆类型、海缆长度、海缆架空线比例下空载容升及单相接地三相断开的工频过电压。结果表明,同等截面下,三芯海缆时工频过电压整体较单芯海缆严重;随着海缆占比增大,混合海缆输电线路由于容升效应导致的工频过电压先增大后减小;对于装机容量为200MW的海上风电场,当海缆长度超过27km时,工频过电压将超过规定的1.3p.u.。     

基于EMTP的同塔并架多回线路防雷计算

通过对110 kV和220 kV单条输电线和同杆并架双回输电线路的防雷性能的仿真和计算,分析研究在多种雷击方式下输电线路的耐雷水平。采用国际通用的电力系统电磁暂态分析的仿真软件Elector-Magnetic Transient Program（EMTP）,对雷电侵入波在输电线路上所产生的过电压进行分析计算,得出过电压分布和变化的规律,进而从技术上和经济上限制雷电侵入波过电压。     

Lightning attachment characteristic of wind turbine generator: Experimental investigation and prediction method based on simulations

As the height of wind turbine increases, the lightning strike accident has become a non-negligible issue. In this paper, the lightning attachment characteristic of a 2-MW wind turbine generator (WTG) is investigated using a model with a reduced scale of 100. The WTG model is equipped with receptors on the blades and a lightning rod on the nacelle, both serving as its external lightning protection system (LPS). The high-voltage electrode, which delivers a lightning impulse voltage from a Marx generator, is used to simulate the final stage of downward negative lightning strikes from 29 coming-leader positions. The experimental results indicate that lightning leaders from either front directions or side directions could be intercepted effectively by LPS, whereas the back-direction lightning could not. Moreover, with the increase of striking distance, the capture ratio for the insulation part of blade decreases. Electric field intensity distribution simulations for the full-scale WTG model, using conditions similar to their experimental counterparts, are conducted and compared with the lightning attachment distribution. Based on classical electro-geometrical model, a simulative method is proposed to predict the lightning attachment distribution of WTG. Our results indicate that it is feasible with this method to produce a satisfactory approximation to the experimentally obtained lightning attachment distribution.     

基于流固耦合的风力机塔筒动态特性分析

塔筒动态特性分析对风力发电机的振动设计起着关键作用。文章以1.5 MW风力发电机塔筒为研究对象,将叶片旋转和随机风载荷作为载荷输入条件,建立风力机塔筒叶片旋转载荷模型、流固耦合风载荷模型、结构动力学方程,分析计算得到随机载荷下叶片旋转和风载共同作用时,风力机塔筒动态特性评估方法。     

线路杆塔接地装置雷电冲击特性仿真计算与模拟试验

杆塔接地装置的冲击接地电阻值直接影响输电线路的防雷效果,降低杆塔冲击接地电阻是降低线路雷击跳闸率的有效措施。采用ATP EMTP仿真计算和模拟雷电冲击试验的方法,对杆塔接地装置的雷电冲击特性进行了研究,设计了一种改进型接地装置。经仿真分析验证,在不改变接地装置覆盖面积的情况下,该装〖JP2〗置比普遍使用的接地装置型式具有更好的雷电冲击特性,可作为高土壤电阻率地区改善线路防雷的有效途径。     

特高压输电线路雷电绕击影响因素及防护措施

针对雷电绕击对特高压输电线路运行可靠性的影响,在总结分析特高压交直流输电线路雷电绕击影响因素的基础上,结合现场运行数据及雷击观测对绕击防护措施的适用性及研究重点进行分析。结果表明,对交直流特高压线路绕击产生影响的因素有运行电压、保护角、地面倾角、杆塔塔型、线路弧垂等;根据地形选取合适的保护角可以将线路整体绕击跳闸率控制在较低水平,但个别塔位仍存在绕击风险;线路避雷器可大幅提升绕击耐雷水平,但大绕击电流、多次回击下避雷器能否承受雷电能量尚需进一步研究;杆塔侧针能大幅减小杆塔附近的绕击概率,但其保护范围能否覆盖线路绕击危险区域是确定其适用性的关键,亦需进一步研究。     

Lightning protection for wind turbine blades and bearings

The protection of wind turbines from lightning damage is increasingly important as they increase in size and are placed in locations where access to carry out repairs may be difficult. As blades are the most common attachment point of lightning, they must be adequately protected. In addition, the passage of lightning current through wind turbine bearings introduces a risk of lightning damage to these vital components. Investigations relating to the improvement of blade lightning protection systems have been carried out, including experiments designed to address the difficult problems involved in the protection of hydraulic cylinders used for tip brake control. Work has also focused on the ability of lightning current to cause damage to wind turbine bearings. The work has been a mixture of computer simulations and experimental testing using high‐voltage and high‐current facilities. Copyright © 2001 John Wiley & Sons, Ltd.     

Influence of blade rotation on the lightning stroke characteristic of a wind turbine

The blades of a wind turbine rotate during normal operation. To investigate the influence of blade rotation on the lightning‐attracting ability of a wind turbine, a discharge test platform is designed for scaled wind turbines. The 50% impulse voltages and flash probabilities of the scaled wind turbines with gap distances of 1 to 8 m in the static and rotary conditions are determined by using the discharge test and selective discharge test. The discharge test for a single wind turbine with a gap of 1 to 2 m indicates that the breakdown voltages of the gap between the scaled turbine and electrodes increases with an increase in the blade rotation speed. However, the discharge test with a gap distance of 4 to 8 m indicates that the breakdown voltage of the fan decreases with an increase in the blade rotation speed. The test results of the scaled dual wind turbines experiment have the same rules. To explain this phenomenon, the influence of wind speed on the space‐charge distribution and electrical field intensity of corona discharge is simulated in the background of a target thundercloud. The rotation of the fan reduces the space‐charge density near the area of the blade tip, which leads to an increase in the field strength near the blade tip of the wind turbine and a decrease in the field strength away from the blade tip. This influence varies in short and long air gap, resulting in opposite relationships between discharge voltage and distance from the tip of the turbine. The results can provide a reference for the lightning protection of wind turbines.     

风剪切下塔影效应对水平轴风力机叶片及风轮气动载荷的影响

采用CFD方法,以NH1500三叶片大型水平轴风力机为研究对象,研究额定风速剪切来流下的塔影效应对水平轴风力机叶片和风轮非定常气动载荷的影响。结果表明：剪切来流下,叶片和风轮的气动载荷均呈余弦变化规律,塔影效应的主要影响叶片方位角范围为160°~210°,且该范围不随风剪切指数的变化而变化。相同风剪切指数下,塔影效应对叶片和风轮气动载荷的均方根影响较小,对其波动影响较大。当风剪切指数从0.12增至0.30时,塔影效应下,叶片气动载荷的均方根减小,推力和转矩的波动幅度增大,偏航力矩和倾覆力矩的波动幅度减小;风轮推力和转矩的均方根减小,波动幅度变化较小,而倾覆力矩和偏航力矩的均方根增大,且波动幅度也增大。