先导放电是长空气间隙击穿过程的主要阶段，也是雷电放电最常见的形式之一。先导放电尤其是流注-先导转换过程的特性与机理，对高压输电工程空气间隙绝缘设计、防雷绕击分析与雷电物理研究均具有重要意义。论文以空气间隙先导放电为主要研究对象，提出了先导放电热特性的定量测试方法，试验获取了先导形成与发展过程中热特性的时空演化规律，同时建立了先导放电的一维热力学自洽模型，对先导放电的热-动力学现象进行解释，并为长间隙放电击穿特性的计算提供了理论依据与参数支持。首先，论文提出了对先导放电热特性进行定量测试的激光干涉方法，通过采用连续激光器为干涉仪光源、CMOS高速摄像仪为干涉图像接收装置，实现了对先导放电热特性的时间分辨观测。以Mach-Zehnder激光干涉平台为主体，建立了先导放电多物理参数同步观测系统，实现了对放电电压、电流、光学形态、先导通道热特性的同步观测。其次， 开展了1 m棒-板间隙在冲击电压下的放电试验，重点对先导起始过程与发展扩张过程的气体动力学现象与热参数演化规律进行了试验观测与定量分析。由时间分辨干涉条纹图像观测到了先导起始过程中的波传播现象、负极性先导通道形成过程的空间预先导及其双向发展现象，同时获得了先导通道热直径扩张规律、先导通道内（包括负极性放电中的空间先导）气体密度与气体温度的时空演化规律等定量参数。第三， 在经典的0维流注-先导转换模型的基础上，考虑放电通道参数的径向分布，融合气体动力学过程与热传导过程、粒子输运过程、细化的能力转换与弛豫过程，建立了先导放电一维热力学自洽模型，可对先导放电过程中的气压、气体密度、气体温度、流速、粒子组分、电场参数等多种物理量的演化规律进行仿真分析，深入阐释流注-先导转换的具体过程与物理机理。最后，利用先导放电一维热力学自洽模型，对先导发展参数与先导热参数进行仿真分析，仿真分析获取的先导通道发展速度、先导通道单位长度电荷量均与试验一致，同时仿真结果可定量解释先导放电过程中的热参数演化规律与先导起始时的波传播现象。
Leader discharge is one of the main phases in long air gap breakdown. Meanwhile, leader is one of the most common processes in lightning phenomena. The investigation on characteristics and mechanisms of leader discharge, especially the streamer-leader transition process, has significant importance on air gap insulation design in high voltage transmission systems, lightning strike analysis and lightning physics illustration. The main purpose of this thesis is to investigate the leader discharge. A quantitative optical mesurements has been put forward to determine the thermal parameterof leader discharge, and the temporal-spatital variation of gas density and gas temperature inside the discharge channel has been obtained. Besides, a one-dimensional (1D) thermo-hydrodynamic model has been established to describe the leader inception and expansion, which is self-consistent. The simulation results provide theoretical references and useful parameters in the evaluation of long air gap breakdown voltages.Firstly, a Mach-Zehnder interferometer has been set up to achieve the quantitative measurements of thermal parameters (thermal diameter, gas density distribution, gas temperature distribution) inside leader channels. The time-resolved interferometry measurements have been realized by using a continuous wave laser as the light source and a CMOS high speed video camera to record the interference images. Based on the Mach-Zehnder interferometer, a synchronized observation platform has been established, which can record the applied voltage, discharge current waveform, luminous morphology of discharge and interference images simultaneously.Secondly, experiements on 1 m rod-palne air gas discharges under impulse voltages have been carried out in laboratory and the heating process of leader channel and related gas dynamic phenomena have been observed. The propagating shockwaves (or sonic waves) accompanying leader formation has been recognized in the time-resolved interference images, and the space leaders (or space stems) and their bi-directional propagation have also been observed. Moreover, quantitative results have been obtained. The thermal diameters and the expansion velocities of leader channels have been measured. The temporal-spatial variations of the gas density and gas temperature distribution (1D and 2D) have also been derived from the interference images by calculating the Abel integral.Thirdly, a 1D thermo-hydrodynamic model has been established based on the classic 0D two-temperature streamer-leader transition model. The 1D leader model is self-consistent when the current injected to the transition zone or leader channel is given. The radial distribution of discharge channel, gas dynamics (including heat conduction), kinetics, detailed energy transfer and transition processes have all been considered. The simulation results of this model can give a relatively full illustration of streamer-leader transition and leader expansion, which will help reveal the physics of leader discharge.Finally, the leader propagating parameters (leader propagation velocity, injected charge needed for leader propagation per length) have been estimated based on the calculation results of the 1D leader model. The calculation results show satisfied agreements with the experimental data obtained both from real-size tower gap discharge tests and 1 m rod-plane discharge tests. Besides, the thermal parameters variations obtained by the simulation also agree with the experimental data derived from the interference images, and the simulation results illustrated the formation of propagation of shockwaves accompanying the leader inception.
