由于風力發電機組獨特的結構、外形、及野外安裝的客觀條件，造成機組經常受到雷擊。

　　雷電不僅對葉片及輪轂造成嚴重損壞，還會導致其它電氣事故，如造成低壓電氣故障及控制系統故障等，雖然在相關標準中，如IECTR61400-24和NRELSR500-31115等文件已經指出如何避免和減少雷擊事故的方法，但還應不斷地尋找的解決方案。

　　本文的作者專注研究于機組的電氣和低壓控制系統，在機組的直擊雷防護上提出了一種新型的基于環形間隙放電器的防雷系統。

　　這種系統由分別安裝在輪轂和塔筒上的環形電極組成，輪轂的環形電極于葉片內部的導雷電纜連接，塔筒的環形電極與塔筒形成可靠的電氣連接，并安裝在水平于輪轂的機艙底部。兩個環形電極的間距保持在1m以內，這樣可以避免輪轂在運動過程中與塔筒上的環形電極造成撞擊而影響機組偏航。當雷電擊中葉片時，雷電流沿葉尖接閃器及導雷電纜將雷電流傳送到輪轂上的環形電極，由于兩個環形電極間存在電位差，所以可以使兩個電極觸發形成雷電通道，最后雷電流通過他同上的環形電極泄放入地。

　　在本文描述的試驗中，實驗者采用了比例尺為1:100的風機模型進行了基本的實驗，同事對風電防雷的前瞻技術進行了討論，這個實驗為這種避雷系統的有效性進行了驗證，相關資料由日本電氣工程師協會及JohnWiley&Sons公司在2006年對外發布。

　　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

　　隨著風電產業的迅猛發展，全球裝機量的激增，機組的并網問題和雷電的防護問題逐步得到了業界的重視，由于機組所處的安裝條件都比較惡劣，并且其自身的結構特點，也是也在環境中較易遭到雷擊。因此，發明一種新型的直擊雷防護措施，已經成了一種必須的措施。

　　雷電對機組的影響已經暴露出來，日本經常會受到嚴重的雷擊侵襲。而最有名的的應該是日本沿海地區獨有的冬季雷暴。實際上，在日本的沿海的風力發電場每年都受到嚴重的雷電影響，同時由于日本冬季雷的電流強度高于世界平均雷電流強度，所以其威力和破壞力也是巨大的。

　　盡管按照相關的標準采取了一定的防護措施，但在對于葉片而言仍沒有更好的防護手段，當雷電擊中機組后雷電流的傳導還存在很多不確定性。

　　所以說在風力發電雷電防護領域還有很多的工作需要進一步完善，一般來講，機組的防雷系統包括：機艙接閃器（測風支架）、葉片接閃器、由于機艙上接閃器的高度和角度不能滿足防護需要，單獨設計避雷塔的費用也較高；盡管葉片上配置有接閃器，也被IEC61400-24這一技術屬性文件明確提出，并作為一種通用方案，但是這并不是最完整有效的防護方法。無論葉片上是否有設計接閃器，對于機組的變槳、主控、發電機、變壓器等低壓電控設備的雷擊事故依然發生。IEC的一篇技術性文章指出：雷電對機組的影響主要集中在低壓電控系統和通信系統，一般來說只要機組中存在低壓電子類裝置，在雷電發生時，低壓電控設備都是受到雷電電磁脈沖的影響及直接在線路上產生的浪涌的侵襲。

　　考慮到機組的特殊情況，作者提出了一種利用兩個環形電極構成的間隙放電器組成的直擊雷防護系統，這種系統最擔心的問題是如何保證雷電流不進入輪轂及機艙，這部分在文中將作為重點討論。通過一個比例尺為1:100參照實際的2MW風力發電機組制作一個模型，并采用這種防雷系統，通過雷擊實驗的方式驗證這套系統的有效性和優勢。

　　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.新型雷電防護系統的提出

　　圖1是常規機組防雷接地系統與概念性防雷系統的說明。通常雷電流是從葉片接閃器通過葉片內部的導雷電纜到達變漿軸承，并且通過變漿軸承向輪轂、主軸在經過偏航軸承通過電纜傳導至接地網。強大的雷電流在塔筒內會產生巨大的雷電電磁脈沖，如果接地線靠近動力和低壓控制電纜，則會產生巨大的影響。

　　因此，常規的接地系統可能加劇雷電對機組低壓控制系統的影響。相反，這種系統利用安裝在輪轂上的環形電極，并且與葉片內部的電纜連接形成導雷通道；另一個環形電極安裝在靠近機艙底部的塔筒上，兩個環形電極分別處于不同的水平軸和垂直軸上，兩個電極間保持一個不到1m的放電間間隙，保持這個間隙的目的在于避免有輪轂和塔筒發生偏轉時可能造成的摩擦以及防止環形電極碰撞造成損壞而影響機艙偏航。當有較大雷電流通過葉片到達環形電極時，由于間隙間存在較高的電場形成兩個電極間的觸發，使雷電流通過兩個環形電極進行放電，這個放電的過程會形成可見的電流通道，由于電流時通過塔筒的外表面而不是內部的導線，所以也會減小雷電電磁脈沖的強度，雷電流會通過塔筒直接入地。

　　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.按比例縮小的試驗用風機模型

　　為了驗證這種防雷系統的有效性，作者做了一個試驗性的測試。用1:100的比例模型，精準的建立一個機組高度為60m，葉輪半徑為39m的風力發電機組模型（模型的機艙高度為60cm,葉輪半徑為39cm，如圖2、3所示），模型葉片采用阻燃的ABS樹脂材料制成，機艙和塔筒采用鐵皮制作。兩個電極采用4mm的銅線制作，輪轂和塔筒上的環形電極直徑分別為5.4cm和7.7cm。在葉片表面采用2mm的搪瓷線模擬葉片接閃器和引下線（導雷電纜），同樣，塔筒上的環形電極采用搪瓷線連接到接地板上，長度約20cm，兩個電極間的距離經過精確地計算，保證間隙不會阻礙葉輪的旋轉。通過CAD制圖工具制作出如圖4所示的實際結構，采用800kV和5Kj脈沖發生器模擬雷電流脈沖，采用1.3/49μs沖擊波形，脈沖電壓為664Kv,如圖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.對模型進行雷擊測試

　　圖6中展示了模型進行雷電沖擊的結果。實驗表明，在輪轂的環形電極于塔筒的環形電極之間產生了點火花，表明雷電流通過間隙放電器進行放電。在圖7中展示了雷電擊中葉片的后緣，而兩個環形電極做組成的間隙放電器同樣觸發并導通，由此證明，這種環形電極組成的間隙放電器是有效的。但圖8、9中也出現了不成功的個案，圖8中由于兩個環形電極之間的距離問題導致雷電流通過輪轂的環形電極于機艙發生閃絡，并沒有通過塔筒上的環形電極；此外，在調整角度后雷電還是擊中了機艙尾部，并沒有擊中機艙上的接閃器和葉片接閃器，雖然擊中了機艙但可以看出兩個環形電極間依然形成了電流通道，在這種條件下可能會導致機組測風系統和低壓控制系統的損壞。圖10中匯總了以上的實驗結果，表明兩個環形電極間隙的距離都應設計成小于輪轂與機艙之間的距離。

　　雖然實驗取得了成功，并且表明調整間隙距離可以達到防雷保護的目的，但最好的解決方案仍需要進一步優化，包括固定的方式，電極的材料、安裝方式，兩個環形電極在動態旋轉中的傾角擺動及誤差率產生的影響。

　　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.結論

　　在這篇文章中作者提出了新型的利用環形電極間隙放電器作為風力發電機組直擊雷防護的一種方法，其中最重要和具有創新性的點在于如何控制兩個環形放電器的間距，使雷電通過間隙時不受風速對電流弧的影響，通過1:100的風機模型及模擬雷擊實驗的結果清楚的表明這種方式是可行的、安全的。雖然在環形電極間隙距離大于輪轂環形電極于機艙間距時會造成輪轂環形電極與機艙的放電，但并不影響該套方案的有效性，通過后續的優化方案這種防雷系統的效果也是能夠令人滿意的。同時作者還在運用FDTD時差法計算，間隙通過雷電流時的電磁抵消情況，但可以肯定的是電磁能量的抵消情況應該與實驗結果相吻合。

　　當然這套防雷系統仍存在一些問題，例如這個系統的定位和安裝需要從工程安裝角度來解決，并且安裝后可能對機組的整體氣動性能方面會存在怎樣的影響，還需要進一步討論。無論如何，這種方案的提出對于機組的雷電防護、實際有效性、安全性能和可實施性都被寄予了很大希望。

　　特別感謝

　　作者感謝大阪大學前講師MatsubaraIchiro博士，在雷電脈沖測試實驗的執行中以及機組的防護方法上提出富有成效的建議以及幫。同時還要感謝YoshiokaTakuma先生、FujiiToshiaki先生和YamashitaShogo先生這些関西大學畢業和沒有畢業學生在雷擊實驗中給予的幫助。