平板电容器是电磁脉冲（EMP）模拟装置中常用的脉冲压缩器件，在平行板电极的SF6沿面闪络实验中发现，原本前沿光滑的纳秒脉冲电压加载在平行板电极上，会在脉冲电压前沿上测得一尖峰，使加载的脉冲电压出现“双峰”现象。为探索该现象的原因，首先通过理论分析，认为该现象可能是由于平行板电极边缘发生了滑闪放电，增大了电极等效正对面积，使平行板电极的等效容值发生突变所致，容值变化越大，尖峰越明显。之后开展了不同气压下平行板电极的沿面闪络实验，并对放电过程的图像进行了拍摄，结果表明：平行板电极边缘产生的树枝状放电在低气压时主干明亮粗大，分枝较多，气压升高后，主干亮度和直径逐渐变小，分枝也越来越少；随着气压的增加，由于平行板电极边缘的滑闪放电受到抑制，平行板的等效面积变化率越来越小，尖峰出现时对应的电压幅值越来越高，且尖峰越来越不明显，与理论分析一致。

During the flashover experiments of parallel-plate electrodes in SF6, a double-peak phenomenon is discovered that a small peak occurs in the front-edge of the applied nanosecond pulse voltage which is originally smooth. In order to explore the cause of this phenomenon, the phenomenon is analyzed theoretically and ascribed to the discharge on the edge of the electrodes. The discharge enlarges the area of the parallel-plate electrodes, thus the equivalent capacitance of the electrodes is increased. The greater the change of the equivalent capacitance is, the more obvious the peak shows. Flashover experiments under different pressures are developed to validate the analysis. The results show that as the pressure increases, the peak is less and less obvious, and the amplitude of the small peak is higher and higher due to the suppression of the discharge in high pressure SF6, which is confirmed by the integrating images of the whole discharge process. Dendritic discharges occur on the edge of the electrodes during the flashover process. In low SF6 pressure, the stems are thick and bright, and generate many branches, but when the pressure is high, the number of stems and branches is reduced and the discharge channel also darkens.