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. Proposal of the Novel Lightning Protection System
　　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).