【作者】 谢施君；

【导师】 何俊佳；

【作者基本信息】 华中科技大学 ， 高电压与绝缘技术， 2013， 博士

【摘要】 雷电是一种常见的自然灾害,其巨大的破坏力每年造成大量的人身伤亡事故和财产损失。雷电防护是能源、交通、航天航空、建筑等诸多领域关注的热点问题。采用负极性地闪模型模拟雷击过程是指导防雷保护装置设计和改造的重要手段。然而,由于现有的负极性地闪模型仍然存在缺陷,部分按照其计算结果设计的防雷保护装置未起到应有的雷电防护效果,亟待提出一种更为合理的雷击过程仿真模型。针对现有模型存在的问题,本文拟提出一种可以反映下行先导曲折、分叉特性、地表电场时空变化以及迎面先导起始和发展物理过程的负极性地闪模型。并围绕负极性梯级先导形成机制、下行先导通道电荷分布、负极性下行先导随机发展模型、正极性迎面先导特性及仿真模型、负极性地闪发展过程三维仿真模型几个方面开展工作。根据负极性流注的能量平衡方程,结合基于电位畸变的空间电荷计算方法,推导了描述负极性流注-先导转化过程的转化区温度计算公式,提出转化区的背景电场是决定负极性梯级先导形成的关键物理参数；通过开展4～10m间隙尺度的负极性长空气间隙放电,获取了负极性梯级尺度、发展速度等放电参数,并通过与自然雷电相关参数进行对比,论证了负极性长间隙放电与自然雷电的相似性；采用外推的方法,提出了雷电梯级先导形成所需的临界背景电场。基于模拟电荷法,根据回击电流积分电荷总量与回击电流峰值的关系,研究了下行先导通道的电荷总量和电荷分布。提出了下行先导通道电荷总量与回击电流峰值的关系；获得了下行先导通道内的电荷分布规律；研究了分支通道对下行先导通道电荷分布的影响,通过引入电荷系数,提出了考虑分支的下行先导通道电荷分布计算方法。采用背景电场作为选择下行先导发展方向的放电参数,建立了负极性下行先导三维随机发展模型；通过对雷电通道的三维几何特征进行分析,建立了分形维数、分支系数以及电荷系数的关系,并根据自然雷电的分形维数,确定了电荷系数和发展概率指数；采用雷电观测结果在分形维数、电荷总量以及地表电场变化三个方面验证了下行先导发展模型的正确性。通过分析雷电下的地表电场时空分布特性,提出了基于电场时空分布等效的正极性迎面先导特性模拟试验方法；设计并开展了避雷针的迎面先导特性模拟试验,获得了初始电晕电荷、电晕起始电压、先导起始电压等放电特征参数；提出了新的流注茎-先导转化临界电荷判据；论证了空间电荷对二次电晕起始的抑制作用；获得了先导初始发展阶段的单位长度电荷量,及单位长度电荷随先导电流的变化趋势。考虑暗区内初始先导的生长和空间电荷对电场的影响,提出了包括流注茎-先导转化热过程和二次电晕起始过程的正极性迎面先导起始模型；结合先导电流计算方法和根据人工引雷试验、迎面先导模拟试验和理论推导提出的先导速度与先导电流的关系,建立了迎面先导发展模型；采用正极性迎面先导模拟试验结果以及自然雷电的迎面先导观测结果对模型进行了验证。结合下行先导三维随机模型和正极性迎面先导起始和发展模型,建立了负极性地闪发展过程三维仿真模型。采用该模型对避雷针的击距、保护半径、引雷范围等防雷性能进行了研究。探讨了电气几何模型对于某个回击电流峰值采用固定击距进行计算可能存在的问题；提出折线法会过于乐观地估计较高避雷针的保护半径；发现了下行先导在近地区域内的侧向发展是导致较高避雷针地表屏蔽失效的主要原因。更多还原

【Abstract】 Lightning flash is a frequent natural disaster, and it causes massive casualties and property losses every year. Therefore, lightning protection is the focus in fields of energy, traffic, aerospace, construction, and et al. Model of negative cloud-to-ground lightning (CG) is the major tool to assist to design and improve lightning protection devices. However, defects in previous CG models lead to incorrect assessment of the performance of lightning protection devices. Therefore, it is extremely urgent to improve the previous CG models.In order to propose a novel improved CG model, which can simulate the tortuous and branched development of downward leader and the physical process of upward leader, a series of studies on the physics mechanism of negative stepped leaders, the charge distributions in downward leaders, the stochastic development model of downward leader, the characteristics and model of positive upward leader were carried out.Base on the energy balance equation in negative streamers and the potential distortion method for calculating the space charge, an equation describing the temperature variation in the streamer-leader transition zone during transformation processes was present. The background electric field in the transition zone was proposed to be the major influencing factor for the development of stepped leader. And the critical background electric field for the development of the stepped leader in natural lightning was proposed by extrapolation method according to the experiment results of negative long air gap discharges.The total charge and charge distribution in downward leader were studies by employing the charge simulation method. A relationship between the total charge and the return stroke current was established, and the distribution law of the charge was obtained. The influence of branched leader on the total charge and charge distribution in downward leader was studied. By introducing a charge factor, a novel calculation method of the charge distribution in branched downward leader was raised.Taking the background electric field as the core parameter for deciding the development direction of stepped leaders, a three-dimensional stochastic model of downward leader was then present. After analyzing the geometric features of simulated lightning channel, the relationships among the fractal dimension, the branched factor, and the charge factor were established. And according to the observational fractal dimension of natural lightning channels, the reasonable values of branched factor and charge factor were chosen. The three-dimensional stochastic model of downward leader was verified by observational results of natural lightning in the aspects of the fractal dimension, the total charge, and the ground electric field.Base on the equivalence of electric field in temporal and spatial (T-S) distribution, a novel simulation test method of positive upward leaders was proposed. After investigating the T-S distribution of electric field in natural lightning, it was found that designing a suitable electrode and choosing a reasonable applied voltage can ensure the equivalence of the simulation test. A series of simulation test on the positive upward leader was carried out, and the critical charge of the stem-leader transition, the shielding effect of space charge on the inception of the second corona, and the charge density of leader were investigated.Considering the initial leader’s propagation and the influence of space charges on electric field, a novel inception model of upward leader including the stem-leader transition and the inception of second corona was proposed. Combining the calculation method of leader current and the relationship between leader velocity and leader current obtained from the artificial triggering lightning experiments, upward leader simulation tests, and physical mechanism, a development model of upward leader was established. This model was verified by simulation tests and observations of natural lightning.Combining the stochastic model of negative downward stepped leaders and the model of positive upward leader by taking the electric field as an intermediary, a simulation model of negative CG flash was established. Using the model, the performances of lightning rods, including the lightning drawing range, the striking distance, and the protection radius on the ground, were investigated and compared with those in the electro-geometrical model (EGM) and the polygon method. And the striking distance in the EGM was found to just reflect the general case. Therefore, objects protected by lightning rods designed using EGM is still possible to be struck. The polygon method is only suitable to assess the performance of lightning rod with a low height, and the assessment for a high lightning rod will be over optimistic. The phenomenon of side striking often happens with a lower lightning current and higher lightning rod. The side development of downward leader is the major reason for the shielding failure of high lightning rods.更多还原