基于多重分形的SF6替代气体击穿特性研究

Research on Breakdown Characteristics of SF6 Substitution Gas Base on Multi-fractal

为探究干燥空气作为SF6替代气体的可能性并深入理解短间隙气体放电流注的放电特性,搭建冲击电压放电试验平台,施加雷电冲击电压和快速暂态过电压,在极不均匀电场下探究干燥空气和SF6气体的绝缘水平。为进一步研究流注形态特性受气体种类、电压极性等外界条件的影响,利用ICCD相机捕获二维流注图像分析了流注发展速度和流注通道长度的关系,并基于多重分形理论对流注整体形态的复杂性进行了解释。结果表明,在0.4MPa的气压下,干燥空气的脉冲击穿电压(V50%)满足24kV C-GIS的基本脉冲绝缘水平;在负极性下分形谱最大值相对较大,流注发展速度更快;与SF6气体下的流注形态相比,空气下的流注形态的分形谱最大值较大,流注发展速度更快;多重分形谱谱宽不随外界条件变化而变化,说明流注光电离在二维图像空间分布上具有一定的相似性。

To explore the possibility of dry-air as a substitute gas for SF6and to understand the discharge characteristics of short gap gas discharge streamer,we set up an experimental platform of impulse voltage discharge and applied the lightning impulse voltage and the fast transient overvoltage to analyze the insulation level of dry-air and SF6gas under the extremely inhomogeneous electric field.To further study the contributions of external conditions such as gas type and voltage polarity to morphological characteristics of the streamer,ICCD camera was used to capture the two-dimensional streamer images,and the relationship between the speed of streamer development and the length of streamer channel was analyzed.And then the complexity of the overall shape of the stream was explained based on the multi-fractal theory.The results were given as follows.The impulse breakdown voltage(V50%)of dry air met the basic impulse insulation level of 24kV C-GIS at 0.4MPa;The maximum value of the fractal spectrum was relatively larger under the negative polarity,and the development speed of the streamer was faster;Compared the changes of the streamer morphological under the SF6,the maximum value of the fractal spectrum was larger,and the development speed of the streamer was faster;The spectral width of the multi-fractal spectrum din not changed with external conditions,which indicated that the streamer photoionization had a certain similarity in the spatial distribution of the two-dimensional image.