Understanding the mechanism of positive leader discharge is important in lightning protection engineering and the external insulation design in high voltage power transmission systems. During the propagation of a positive leader, some processes without light-emitting, for example, the insulation recovery process after the breakdown, cannot be observed by optical photography techniques. With the combination of the digital high-speed imaging system, the conventional Schlieren techniques offer new vistas in the long air gap discharge observation. The important features of high spatial resolution, high sensitivity, and easy arrangement make Schlieren techniques powerful and effective tools for characterising the discharge processes without light-emitting. This work presents a brief review of current Schlieren techniques and discusses the design of the Schlieren optics system for long spark observations. Several interesting phenomena discovered at different phases of long sparks with high-speed Schlieren techniques are also presented.

中文翻译：

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观察长正火花的纹影技术：回顾与应用

了解正先导放电的机理对于防雷工程和高压输电系统的外绝缘设计具有重要意义。在正极引线的传播过程中，一些不发光的过程，例如击穿后的绝缘恢复过程，是无法通过光学摄影技术观察到的。结合数字高速成像系统，传统纹影技术为长气隙放电观察提供了新的视角。高空间分辨率、高灵敏度和易于排列的重要特征使纹影技术成为表征不发光放电过程的强大而有效的工具。这项工作简要回顾了当前的纹影技术，并讨论了用于长火花观测的纹影光学系统的设计。还介绍了使用高速纹影技术在长火花的不同阶段发现的几种有趣现象。