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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。
