由于风力发电机组独特的结构、外形、及野外安装的客观条件，造成机组经常受到雷击。

　　雷电不仅对叶片及轮毂造成严重损坏，还会导致其它电气事故，如造成低压电气故障及控制系统故障等，虽然在相关标准中，如IECTR61400-24和NRELSR500-31115等文件已经指出如何避免和减少雷击事故的方法，但还应不断地寻找的解决方案。

　　本文的作者专注研究于机组的电气和低压控制系统，在机组的直击雷防护上提出了一种新型的基于环形间隙放电器的防雷系统。

　　这种系统由分别安装在轮毂和塔筒上的环形电极组成，轮毂的环形电极于叶片内部的导雷电缆连接，塔筒的环形电极与塔筒形成可靠的电气连接，并安装在水平于轮毂的机舱底部。两个环形电极的间距保持在1m以内，这样可以避免轮毂在运动过程中与塔筒上的环形电极造成撞击而影响机组偏航。当雷电击中叶片时，雷电流沿叶尖接闪器及导雷电缆将雷电流传送到轮毂上的环形电极，由于两个环形电极间存在电位差，所以可以使两个电极触发形成雷电通道，最后雷电流通过他同上的环形电极泄放入地。

　　在本文描述的试验中，实验者采用了比例尺为1:100的风机模型进行了基本的实验，同事对风电防雷的前瞻技术进行了讨论，这个实验为这种避雷系统的有效性进行了验证，相关资料由日本电气工程师协会及JohnWiley&Sons公司在2006年对外发布。

　　1.Introduction

The installation of wind turbine has grown explosively worldwide; however, problems regarding interconnectivity to grids have arisen. It has also been pointed out that wind power generation facilities are exposed to lightning damage owing to their configurations, and so protective measures different from those needed for conventional generators are necessary. This problem has recently surfaced as an important issue [1–7].Japan, especially suffers from frequent and heavy lightning strikes, an example being the notorious ‘winter lightning’ found in coastal areas of the Sea of Japan[8]. Indeed, many turbines in Japan have been hit by lightning, and winter lightning poses a specific threat due to its intense power and electric current which are much higher than the world average [7,9]. Although some of the above-mentioned reports describe these incidents and methods of protection, there appear to have been few investigations into insulation schemes, lightning protection design and transient analysis for the latest generation of apparatus. While blade protection has been relatively well discussed [7], the behavior of the wind turbine experiencing surge propagation during a lightning stroke has yet to be clarified.
There is room for more work to be done in this area. In general, lightning protection for wind power generation includes a lightning pole on a nacelle, an independent lightning pole tower and a receptor on the top end of a blade. But the lightning pole on the nacelle cannot obtain enough height owing to weight and wind pressure, and an independent lightning tower greatly increases the construction costs.
Though the third solution, the receptor on a blade, recommended in IEC61400-24 [5], appears the best solution for lightning protection, it is not a complete solution. Despite the existence of such receptors, dielectric accidents still occur on wind power turbines including blades, the generator, the transformer and lowvoltage circuits [7].
According to an IEC report [5], the most frequent accident is dielectric breakdown on low-voltage circuits including electric and telecommunication equipment. In general, electrical and electronic equipment for wind power generation are set up close to or inside a wind tower. Once lightning strikes the wind turbine, assuming that it hits a receptor of one of the blades, a lightning current surge propagates through a down-conductor in the blade, a carbon brush or arc horn near the bearings,and the grounding conductor inside a wind tower (or,in another case, the current may flow through the conductive tower itself). The low-voltage circuit in the wind turbine is easily broken by electromagnetic induction in such a situation. Considering the above, the author proposes a novel lightning protection system that has two ring-shaped electrodes. The principal concern of the proposed system is to prevent the lightning surge from affecting the wind turbine as well as the nacelle and the tower.
This paper discusses an impulse experiment utilizing the proposed system in a downsized wind tower accurately simulating an actual 2 MW wind turbine on a 1/100 scale. Attaching the proposed ring-shaped electrodes to the downsized wind turbine, the author demonstrates that the system provides effective lightning protection.

　　1.前言

　　随着风电产业的迅猛发展，全球装机量的激增，机组的并网问题和雷电的防护问题逐步得到了业界的重视，由于机组所处的安装条件都比较恶劣，并且其自身的结构特点，也是也在环境中较易遭到雷击。因此，发明一种新型的直击雷防护措施，已经成了一种必须的措施。

　　雷电对机组的影响已经暴露出来，日本经常会受到严重的雷击侵袭。而最有名的的应该是日本沿海地区独有的冬季雷暴。实际上，在日本的沿海的风力发电场每年都受到严重的雷电影响，同时由于日本冬季雷的电流强度高于世界平均雷电流强度，所以其威力和破坏力也是巨大的。

　　尽管按照相关的标准采取了一定的防护措施，但在对于叶片而言仍没有更好的防护手段，当雷电击中机组后雷电流的传导还存在很多不确定性。

　　所以说在风力发电雷电防护领域还有很多的工作需要进一步完善，一般来讲，机组的防雷系统包括：机舱接闪器（测风支架）、叶片接闪器、由于机舱上接闪器的高度和角度不能满足防护需要，单独设计避雷塔的费用也较高；尽管叶片上配置有接闪器，也被IEC61400-24这一技术属性文件明确提出，并作为一种通用方案，但是这并不是最完整有效的防护方法。无论叶片上是否有设计接闪器，对于机组的变桨、主控、发电机、变压器等低压电控设备的雷击事故依然发生。IEC的一篇技术性文章指出：雷电对机组的影响主要集中在低压电控系统和通信系统，一般来说只要机组中存在低压电子类装置，在雷电发生时，低压电控设备都是受到雷电电磁脉冲的影响及直接在线路上产生的浪涌的侵袭。

　　考虑到机组的特殊情况，作者提出了一种利用两个环形电极构成的间隙放电器组成的直击雷防护系统，这种系统最担心的问题是如何保证雷电流不进入轮毂及机舱，这部分在文中将作为重点讨论。通过一个比例尺为1:100参照实际的2MW风力发电机组制作一个模型，并采用这种防雷系统，通过雷击实验的方式验证这套系统的有效性和优势。

　　2.ProposaloftheNovelLightningProtectionSystem

Figure 1 is a conceptual illustration of a conventional system and the proposed system of lightning protection for wind turbines. Generally, in the conventional system,the lightning current flows from one of the receptors installed on the top end of a blade to the ground via a down-conductor in the blade, brush or arc-horn near the bearing, and a grounding-wire (or sometimes the body of the tower itself).
The surge current flow inside the tower may create a large inductive current in low-voltage circuits such as control, measurement and communication devices. Thus, the conventional grounding system is potentially weak for the protection of low-voltage circuits inside the wind turbine. By contrast, the proposed system has two ring-shaped electrodes of several meters diameter, one of which is vertically attached to the nose cone and the other laterally placed on top of the wind tower lying just below the nacelle.
 The pair of rings is arranged with a narrow gap of no more than 1 m to avoid mechanical friction during rotation of the blades and the nacelle’s circling. When lightning (here, suppose the current is positive)strikes a blade, the lightning current reaches the upper ring from a receptor through a conductive wire installed on the blade.
Then, the electric field between the two rings becomes high and finally sparks over and the lightning current flows downwards. The current propagates along the lower ring and grounding wire,which is arranged outside the wind tower rather than inside, and is safely led to a grounding electrode sited far enough away from the grounding for the tower.

　　2.新型雷电防护系统的提出

　　图1是常规机组防雷接地系统与概念性防雷系统的说明。通常雷电流是从叶片接闪器通过叶片内部的导雷电缆到达变浆轴承，并且通过变浆轴承向轮毂、主轴在经过偏航轴承通过电缆传导至接地网。强大的雷电流在塔筒内会产生巨大的雷电电磁脉冲，如果接地线靠近动力和低压控制电缆，则会产生巨大的影响。

　　因此，常规的接地系统可能加剧雷电对机组低压控制系统的影响。相反，这种系统利用安装在轮毂上的环形电极，并且与叶片内部的电缆连接形成导雷通道；另一个环形电极安装在靠近机舱底部的塔筒上，两个环形电极分别处于不同的水平轴和垂直轴上，两个电极间保持一个不到1m的放电间间隙，保持这个间隙的目的在于避免有轮毂和塔筒发生偏转时可能造成的摩擦以及防止环形电极碰撞造成损坏而影响机舱偏航。当有较大雷电流通过叶片到达环形电极时，由于间隙间存在较高的电场形成两个电极间的触发，使雷电流通过两个环形电极进行放电，这个放电的过程会形成可见的电流通道，由于电流时通过塔筒的外表面而不是内部的导线，所以也会减小雷电电磁脉冲的强度，雷电流会通过塔筒直接入地。

　　3.DownsizedModelofWindTurbine

To verify the effectiveness of the proposed lightning protection system, the author conducted a trial test using a 1/100 downsized model that on a 1/100 scale accurately simulated an actual 2 MWwind turbine with a hub height of 60 m and a blade radius of 39 m (therefore, the hub height of the model is 60 cm and the blade radius 39 cm, as shown in Figs 2 and 3). The blades of the model are made from nonflammable ABS resin and the nacelle and  tower from PC iron.

The ring-shaped electrodes of the model are of 4 mm φ copper wires, and the diameter of the upper and lower electrodes are 5.4 and 7.7 cm, respectively. On the surface of the blades, 2 mm φenamel wires are strained to simulate receptors and down conductors. Also, as the outer down conductor, 2 mm φenamel wires drop down from the backside of the lower ring to the ground plate which is 20 cm distant from the base of the wind tower. The gap between two rings, g,and the distance between the upper ring and the nacelle,d, are design variables in the model. A detailed structure is shown in Fig. 4 in a CAD drawing and a photo of a prototype. Simulated lightning impulses with a wavefront of 1.3 μs, wavetail 49 μs, altitude 664 kV were generated using a 800 kV and 5 kJ impulse generator, as shown as Fig. 5.

   3.按比例缩小的试验用风机模型

　　为了验证这种防雷系统的有效性，作者做了一个试验性的测试。用1:100的比例模型，精准的建立一个机组高度为60m，叶轮半径为39m的风力发电机组模型（模型的机舱高度为60cm,叶轮半径为39cm，如图2、3所示），模型叶片采用阻燃的ABS树脂材料制成，机舱和塔筒采用铁皮制作。两个电极采用4mm的铜线制作，轮毂和塔筒上的环形电极直径分别为5.4cm和7.7cm。在叶片表面采用2mm的搪瓷线模拟叶片接闪器和引下线（导雷电缆），同样，塔筒上的环形电极采用搪瓷线连接到接地板上，长度约20cm，两个电极间的距离经过精确地计算，保证间隙不会阻碍叶轮的旋转。通过CAD制图工具制作出如图4所示的实际结构，采用800kV和5Kj脉冲发生器模拟雷电流脉冲，采用1.3/49μs冲击波形，脉冲电压为664Kv,如图5所示。

　　4.ImpulseTestinaDownsizedModel

Figure 6 presents an example of the results of an impulse test using the 1/100 downsized wind turbine model with the proposed ring-shaped electrodes. As shown in the figure, spark-over successfully occurred between the two electrodes, showing that the lightning current was safely led to a grounding electrode through the outer down conductor.In another case shown in Fig. 7, the lightning struck backward of the wind turbine.

Thus, the result of the impulse test demonstrated that the proposed two ring-shaped electrode system is effective for lightning protection for electrical and electronic devices in a wind turbine.On the other hand, the result shown in Fig. 8 is an example of an unsuccessful case. In this case, where the gap between two rings, g, is less than the distance between the upper ring and the nacelle d, spark-over often tends to occur between the upper ring and the nacelle and the lightning current unexpectedly rushes to the inside or surface of the nacelle and the tower.

This may cause the breakdown or burnout of low-voltage and control circuits installed in a wind turbine. Moreover,Fig. 9 shows another type of an unsuccessful result,where the lightning directly struck backward of the nacelle in spite of the receptor on the blade.The graphs shown in Fig. 10 summarize the aboveresults. Graphs of positive and negative lightning currents clarify that the gap for the two rings should be designed to be lower than the distance between the upper ring and the nacelle.

Although the result shows that a lower gap may make for a safer operation, the best solution needs to be considered from standpoints including the method of fixation, the weight of materials, installation costs and the effect of flexural oscillation of the rings during rotation of the blades.

　　4.对模型进行雷击测试

　　图6中展示了模型进行雷电冲击的结果。实验表明，在轮毂的环形电极于塔筒的环形电极之间产生了点火花，表明雷电流通过间隙放电器进行放电。在图7中展示了雷电击中叶片的后缘，而两个环形电极做组成的间隙放电器同样触发并导通，由此证明，这种环形电极组成的间隙放电器是有效的。但图8、9中也出现了不成功的个案，图8中由于两个环形电极之间的距离问题导致雷电流通过轮毂的环形电极于机舱发生闪络，并没有通过塔筒上的环形电极；此外，在调整角度后雷电还是击中了机舱尾部，并没有击中机舱上的接闪器和叶片接闪器，虽然击中了机舱但可以看出两个环形电极间依然形成了电流通道，在这种条件下可能会导致机组测风系统和低压控制系统的损坏。图10中汇总了以上的实验结果，表明两个环形电极间隙的距离都应设计成小于轮毂与机舱之间的距离。

　　虽然实验取得了成功，并且表明调整间隙距离可以达到防雷保护的目的，但最好的解决方案仍需要进一步优化，包括固定的方式，电极的材料、安装方式，两个环形电极在动态旋转中的倾角摆动及误差率产生的影响。

　　5.Conclusions

In this paper the author has proposed a novel method that utilizes two ring-shaped electrodes for lightning protection of wind turbines. The most important and innovative point of the proposed system is a pair of ringshaped electrodes arranged with a narrow gap, where the air discharges to flow the surge current when a lightning strikes the wind turbine.1/100 downsized model of a wind turbine with ring electrodes was manufactured. The results of impulse experiments clearly showed that the proposed model can operate safely.
Especially, when the gap between the two rings is larger than the distance between the upper ring and the nacelle, it is clear that a spark-over certainly occurs and the lightning protection system functions satisfactorily.The author is also investigating FDTD electromagnetic calculations for the present model [10,11].It was confirmed that the results of the calculations also agree well with the experimental results.
 problems remain for the proposed method. For example, the method of fixation and installation costs need resolving from a civil engineering viewpoint. Also, any adverse impact on power generation capacity should be discussed from the viewpoint of fluid dynamics. However, in respect of lightning protection, i.e. utilized capacity and generating cost, the proposed system can be expected to maintain the reliability and safety of operations for wind power generation.
Acknowledgements
The author thanks Dr. Matsubara Ichiro, former lecturer of Osaka University, for his help in the operation of impulse testing and for a fruitful discussion on the methodology of lightning protection. The author also thanks Mr. Yoshioka Takuma, Mr. Fujii Toshiaki and Mr. Yamashita Shogo, graduate and undergraduate students of Kansai University, for their help in the impulse tests.

　　5.结论

　　在这篇文章中作者提出了新型的利用环形电极间隙放电器作为风力发电机组直击雷防护的一种方法，其中最重要和具有创新性的点在于如何控制两个环形放电器的间距，使雷电通过间隙时不受风速对电流弧的影响，通过1:100的风机模型及模拟雷击实验的结果清楚的表明这种方式是可行的、安全的。虽然在环形电极间隙距离大于轮毂环形电极于机舱间距时会造成轮毂环形电极与机舱的放电，但并不影响该套方案的有效性，通过后续的优化方案这种防雷系统的效果也是能够令人满意的。同时作者还在运用FDTD时差法计算，间隙通过雷电流时的电磁抵消情况，但可以肯定的是电磁能量的抵消情况应该与实验结果相吻合。

　　当然这套防雷系统仍存在一些问题，例如这个系统的定位和安装需要从工程安装角度来解决，并且安装后可能对机组的整体气动性能方面会存在怎样的影响，还需要进一步讨论。无论如何，这种方案的提出对于机组的雷电防护、实际有效性、安全性能和可实施性都被寄予了很大希望。

　　特别感谢

　　作者感谢大阪大学前讲师MatsubaraIchiro博士，在雷电脉冲测试实验的执行中以及机组的防护方法上提出富有成效的建议以及帮。同时还要感谢YoshiokaTakuma先生、FujiiToshiaki先生和YamashitaShogo先生这些関西大学毕业和没有毕业学生在雷击实验中给予的帮助。