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1、1.1 气体放电的基本物理过程 1.1 The physical process of the gas discharge,高压电气设备中的绝缘介质有气体、液体、固体以及其它复合介质。由于气体绝缘介质不存在老化问题，击穿后自愈能力强，且其成本廉价，因此气体成为了在实际应用中最常见的绝缘介质。 The insulation used in a high voltage electrical apparatus can be gas, solid, liquid, or other composite dielectric. As the gaseous insulation doesnt hav
2、e the aging problem, coupled with complete insulating self-recovery characteristic after breakdown and also low cost, it has become the most common dielectric in the practical applications.,气体击穿过程的理论研究虽然还不完善，但是相对于其他几种绝缘材料来说最为完整。因此，高电压绝缘的论述一般都由气体绝缘开始。 Although the theoretical study on the gas breakdo
3、wn is still not perfect, compared with the other kinds of insulating materials, it is the most complete. Therefore, we put the gas insulation at the very beginning.,本节内容 Contents in this section,1.1.1 带电质点的产生 1. 1. 1 The generation of charged particles 1.1.2 带电质点的消失 1. 1. 2 The disappearance of char
4、ged particles 1.1.3 电子崩与汤逊理论 1. 1. 3 The electron avalanche and Townsend Theory 1.1.4 巴申定律与适用范围 1. 1. 4 Paschens law and scope of application 1.1.5 气体放电的流注理论 1. 1. 5 Streamer theory of gas discharge 1.1.6 不均匀电场中的气体放电 1. 1. 6 The gaseous discharge in non-uniform fields,1.1.1 带电质点的产生 1. 1. 1 The gener
5、ation of charged particles,气体放电是对气体中流通电流的各种形式统称。 Gas discharge is the generic terms of various forms of flowing current in gas.,由于空气中存在来自空间的辐射，气体会发生微弱的电离而产生少量的带电质点。 Due to any external radiation (such as ultra-violet illumination), the gas will ionize weakly and produce a small mount of charged part
6、icles.,正常状态下气体的电导很小，空气还是性能优良的绝缘体； Gas in normal state with small conductance is almost a perfect insulator; 在出现大量带电质点的情况下，气体才会丧失绝缘性能。 Gas will not lose insulating property until a large number of charged particles produced.,1、气体中电子与正离子的产生 Production of electrons and positive ions in gas,电离是指电子脱离原子核的
7、束缚而形成自由电子和正离子的过程。电离可一次完成，也可以是先激励再电离的分级电离方式。 Ionization refers to the process that the electron divorced from the shackles of nucleus generating free electrons and positive ions. Ionization can be completed at one time or be motivated firstly then ionized (ionization by step),电子在电场中的运动轨迹 Electron-tra
8、jectory in the electric field,视频链接,（1）热电离 Thermoionization,常温下，气体分子发生热电离的概率极小。 At normal temperature, the probability of gas thermoionization is very low.,气体中发生电离的分子数与总分子数的比值m称为该气体的电离度。 The ratio m of the number of ionized molecules and the total number of molecules is called ionization degree of th
9、e gas.,图1-1 不同温度下空气和气体的热电离程度 Figure 1-1 Thermal ionization degree of air and SF6 at different temperatures,下图为不同温度下空气和SF6气体的热电离程度。 The following picture shows the thermal ionization degree of air and SF6 at different temperatures.,（2）光电离 Photoionization,（3）碰撞电离 Collision ionization,(1-3),电子或离子在电场作用下
10、加速所获得的动能( )与质点电荷量(e)、电场强度( )以及碰撞前的行程( )有关即: The kinetic energy ( ) obtained by electron or ion with the acceleration of the electric field depends on the particle quantity (e), electric field strength ( ) and the distance ( ) of electron moved before collision. That is:,高速运动的质点与中性的原子或分子碰撞时，如原子或分子获得的
11、能量等于或大于其电离能，则会发生电离。 High-speed particles make inelastic collisions with atoms (or molecules), if the energy being gained is greater than or equal to ionization energy, then collision ionization occurs.,(1-4),因此，电离条件为 So, the condition below defines the onset of ionization,式中where： ：电子的电荷量； Quantity
12、of electric charge ：外电场强度； External electric field strength ：电子移动的距离 Distance of the electron moved,（4）分级电离 Hierarchical ionization,电子在外界因素的作用下可跃迁到能级较高的外层轨道，称之为激励，其所需能量称为激励能。 Electrons due to the influence of external factors can jump to outer orbits of higher energy level , called the excitation, a
13、nd the energy needed is called exciting energy .,原子或分子在激励态再获得能量而发生电离称为分级电离，此时所需能量为 。 Atoms or molecules in excited state gain more energy and result in ionization, which is called grading ionization, and the energy needed is .,为使碰撞能导致电离，质点在碰撞前必须经过的距离为： The minimum distance electron must move to caus
14、e collision ionization is:,式中 为气体的电离电位，在数值上与以eV为单位的 相等 Where, is the ionization voltage, which is equal to with the unit eV numerically.,的大小取决于场强E，增大气体中的场强将使 值减少。可见提高外加电压将使碰撞电离的概率和强度增大。 depends on the electric field intensity E, that is to say increasing field strength makes the value of decreasing.
15、 Obviously, both the probability and intensity of collision ionization will be enhanced with the increase of the applied voltage.,2、电极表面的电子逸出 Electronic escape form the electrode surface,逸出功使电子从金属表面逸出需要的能量。 Work function: the energy to make the electron escape from the surface of the metal.,不同金属的逸出功
16、不同，如表1-2所示。 Work function varies in different metal, as shown in Table 1-2.,电子从电极表面逸出所需的能量可通过下述途径获得 ： Escape of electrons from the electrode surface, the energy required can be obtained in the following ways：,（1）正离子撞击阴极 Positive ion strikes on the surface of negative pole （2）光电子发射 Photoelectric emission （3）强场发射 Strong field emission （4）热电子发射 Thermoionic emission,3、气体中负离子的形成 Formation of negative ions in gas,附着：电子与气体分子碰撞时，不但有可能引起碰撞电离而产生出正离子和电子，也
