近年来，超特高压直流输电技术得到快速发展，在跨区域电网间的互联与大容量远距离输电等场景获得广泛应用。接地极线路是超/特高压直流输电系统的重要组成部分，是直流系统不平衡电流和大地回流的入地通道，具有承载电流大、线路电压低的特点，其外绝缘配置较低，易遭受雷电和操作过电压的影响。招弧角包括一对并联安装于绝缘子串两端的电极，电极形成的间隙长度略小于绝缘子串长度，当接地极线路遭受过电压冲击时，先于绝缘子串击穿，从而起到保护绝缘子串进而保护接地极线路的作用，对保证超/特高压直流输电系统安全可靠运行具有重要意义。招弧角击穿引发的接地极线路直流电弧具有电流幅值大、燃烧时间长、难以熄灭的特点，我国已多次发生直流电弧导致的接地极线路掉串、断线事故，甚至引发直流系统闭锁停运，造成国民经济重大损失。处于户外开放空间下的接地极线路直流电弧受电极型式、环境等因素影响，其燃弧过程极为复杂。如能在招弧角间隙击穿产生电弧时，及时将其转移至电极端部，从而避免对绝缘子的破坏，并创造有利条件，使其快速熄弧，不但可以减少接地极线路因无法及时有效熄弧导致的故障或停运，保证电力的持续输送，而且可有效保障直流系统的稳定运行，防止发生更大电力系统事故。因此，有必要深入理解接地极线路直流电弧电气特性、运动特性，掌握其内在物理机制，为进一步研究可靠性高、经济性好的直流电弧熄弧方法提供理论依据。为研究直流电弧热、电、磁、力等物理场分布特性，本文建立了电弧磁流体动力学模型，实现了直流电弧各物理场和运动状态的耦合。进一步建立了百千瓦容量接地极线路直流电弧模拟试验平台，可以清晰捕获电弧形态，也可以获取直流电弧电流、电压等电气参数，为研究直流电弧电气特性和运动特性奠定了基础。仿真结果与试验结果典型特征相符，从而验证了该仿真模型的有效性。为研究直流电弧的电气特性，设计了一系列试验测得接地极线路直流电弧全过程电压和电流，深入研究电极结构、外部风场和磁场对电弧电气特性的影响规律，研究了直流电弧运动过程中的电气特性及其影响因素。通过试验发现电弧初始和熄灭阶段，电流产生激烈振荡。电弧运动过程中，频繁发生的弧柱短接和弧根跳跃，造成电压跌落和电流脉冲，其幅度随风速增大而减小。研究发现，增大间隙距离，电弧电压曲线整体向上平移，燃弧时间也随之减小。当电极扩张角度增大时，电压增长越快。通过试验对比，发现双羊角形招弧角电弧电压的增长率比单羊角形更高，表明双羊角形电极对电弧的拉伸作用优于单羊角形电极。通过分析，得到了直流电弧伏安特性曲线，并拟合得到电弧电位梯度，发现电弧电位梯度随电流的增大而减小。电弧电压是维持电弧的关键因素，电弧电压最大值大于电源电压，当电压达到最大值后电弧开始熄灭。为研究直流电弧运动特性，通过高速摄像机记录电弧运动轨迹，研究不同风速、磁场强度、电极扩张角度等因素对电弧的影响。发现电弧受热浮力作用整体向上偏移，弧柱更靠近招弧角上电极，导致弧根跳跃多发生于上电极。上弧根运动速度大于下弧根，通过仿真发现下弧根前进方向区域形成的气旋阻碍了下弧根的运动。由于弧根运动至招弧角电极端部后停留时间较长，导致该处的烧蚀作用更为强烈。通过改变电极的扩张角度，发现电极对电弧的纵向拉伸作用随扩张角增大而增大，对电弧的横向疏导作用则随之减小。研究还发现随着扩张角增大，弧根跳跃的频次增大，同时弧柱也更靠近电极，使间隙出现残留高温，不利于熄弧。由于扩张角增大，热浮力垂直分量增大，使得上弧根体积力增大，弧根运动也更为迅速。对比分析发现招弧角电极扩张角存在一个角度可以兼顾对电弧的拉伸性能和疏导性能。研究了风场对电弧的作用，发现风对弧柱的作用大于对弧根的作用，风加强了对电弧的扩散和冷却作用，促进电弧更快熄灭，弧根跳跃和弧柱短接发生的次数随风速的增大而减少。研究了磁场对电弧的影响，发现磁场对弧根的作用大于对弧柱的作用，磁场越大弧根与电极的夹角越小。弧柱在电磁力的驱动下产生螺旋运动，磁场越大，螺旋运动的空间尺寸也更大。为解决接地极线路直流电弧熄弧难的问题，本文提出了基于金属氧化物阀片的直流电弧自熄弧方法，设计了带熄弧单元的招弧角。首先建立直流接地极系统的电磁暂态仿真模型，该模型包括直流电流源、架空导地线、杆塔和接地电阻、接地极电阻、雷电流、招弧角和熄弧单元等模块。通过仿真计算，发现当超/特高压直流输电系统在单极大地运行模式下，接地极线路遭受雷击导致招弧角击穿时，电弧电流和电压沿接地极线路从换流站到接地极极址方向逐渐减小，雷击点越靠近换流站，导致的后果将比靠近接地极侧更加严重。提出熄弧单元的吸收能量决定了招弧角的熄弧能力，熄弧单元需满足的最小吸收能量由招弧角遭受雷击时的电气特性决定。研究发现接地极线路运行电流大小对熄弧单元吸收能量的影响较小，因为熄弧单元可以迅速切断电弧，其吸收的能量以雷电能量为主。最后，根据仿真计算结果，设计了氧化锌阀片参数，试制了带自熄弧功能的新型招弧角，试验表明该新型招弧角性能符合要求，满足接地极线路实际需要。本文探明了接地极线路直流电弧特性，为今后更深入研究直流电弧提供理论依据，提出了直流电弧熄弧方法，对于解决超特高压直流输电接地极线路熄弧问题有重要的指导意义。

Recently, extra-high voltage (EHV) and ultra-high voltage (UHV) direct current (DC) transmission technology has been rapidly developed and widely applied in cross-regional grids interconnection and large-capacity long-distance power transmission. The grounding electrode line is an important part of the EHV/UHV DC transmission system, which provides a grounding channel for both unbalanced current and ground return current. It has the characteristics of large current and low voltage. Due to its low external insulation level, it is vulnerable to lightning and switching overvoltage. The arcing horn consists of a pair of electrodes installed in parallel at both ends of the insulator string. The air gap between the electrodes is slightly smaller than the length of the insulator string, so that the lightning impulse flashover voltage is smaller than that of the insulator string. Therefore, the arcing horn will break down before the insulator string when an overvoltage fault occurs, protecting the insulators and the grounding electrode line, therefore ensures the safety and reliability of the EHV/UHV DC transmission system. The DC arc on arcing horn is characterized of large current amplitude, long burning time and difficulty to extinguish. In recent years, there have been many accidents caused by the DC arc on arcing horn, such as conductor fracture and string falling apart, and eventually lead to EHV/UHV DC transmission system closedown with great cost of the national economy.The DC arc of grounding electrode line under outdoor open space is influenced by the electrode type, environment and other factors, and its ignition process is extremely complex. If the DC arc can be transferred to the end of the electrode in time to avoid damage to the insulators and create favorable conditions for rapid arc extinction, it can reduce the fault or outage of the grounding electrode line to ensure the stable operation and reliable power supply of the EHV/UHV DC transmission system, and prevent the large power grid accidents. Therefore, it is necessary to characterize the electrical and motion properties of the DC arc of grounding electrode line with a deep understanding of its underlying physical mechanism. A fundamental theory underlying the DC arc extinguishing would facilitate its potential improvement in reliability and cost-effectiveness.In order to study the characteristics of thermal, electrical, magnetic and force of the DC arc, a magnetohydrodynamic model (MHD) of the arc considering thermal buoyancy was established, which realized the coupling of physical fields and motion state of the DC arc. We also built a 10² kW experimental platform for the DC arc of grounding electrode line to capture the arc shape and measure the electrical parameters such as current and voltage. It provides a basis for studying the electrical characteristics and motion characteristics of the DC arc. The simulation results were consistent with the experimental results, which verified the effectiveness of the model.In order to study the electrical characteristics of the DC arc, we measured the voltage and the current of the whole DC arc process, the influence of the electrode, wind speed and magnetic field on the electric characteristics of the arc was studied, and the influence of the DC arc motion on electrical characteristics was studied too. From these experiments, it is found that the arc current oscillates violently during the initial and extinguishing stages. During the arc movement, the frequent short-circuit of the arc column and the jump of the arc root cause the voltage drop and the current pulse, the amplitude of which decreases with the increase of the wind speed. It is found that as the gap distance increases, the arc voltage curve shifts upward as a whole, and the arcing time also decreases. The voltage increases faster when the expansion angle of the electrode increases. Through experimental comparison, the growth rate of the arc voltage of the double arcing horn is higher than that of the single arcing horn, indicating that the double arcing horn has a better stretching effect. The DC arc volt-ampere characteristic curve is obtained, and the arc potential gradient is fitted. It is found that the arc potential gradient decreases with the increase of the current. Voltage is the key factor to maintain the arc. The maximum value of the arc voltage is greater than the power supply voltage. The arc begins to extinguish when the voltage reaches the maximum value.In order to study the motion characteristics of the DC arc, the arc trajectory was recorded by a high-speed camera, and the effects of different wind speed, magnetic fields, and the expansion angle of the electrodes on the arc were studied. It is found that the arc shift upward due to thermal buoyancy, and the arc column is closer to the upper electrode of the arcing horn, resulting in the arc root jump mostly occurring at the upper electrode. The upper arc root moves faster than the lower arc root, and the simulation results show that the cyclone formed in front of the lower arc root hinders the movement of the lower arc root. The ablation at the end of the upper electrode is more serious, because the upper arc root moves to the end of the electrode and stays for a long time. By changing the expansion angle of the electrode, it is obtained that with the increase of the expansion angle, the longitudinal stretching effect on the arc increases, and the lateral transfer effect decreases. Besides, it is also found that with the increase of the expansion angle, the arc root jumps more frequently, and the arc column is closer to the electrode, leaving high temperature in the gap, which is not conducive to arc extinguishing. As the expansion angle increases, the thermal buoyancy effect increases, which increases the volume force of the upper arc root and makes the arc root move more rapidly. It is found that there is an expansion angle of the electrode which can give consideration to both the extension and transfer of the arc. The effect of the wind speed on the arc was studied. It is found that the effect of the wind on the arc column is greater than that on the arc root. The wind strengthens the diffusion and cooling of the arc and promotes the arc extinction. The number of the arc root jump and the arc column short circuiting decreases with the increase of the wind speed. The influence of magnetic field on arc was studied. It is found that the effect of magnetic field on arc root is greater than that on arc column. The angle between the arc root and the electrode decreases with the increase of the magnetic field. The arc column is driven by the electromagnetic force to produce a spiral, and the space size of the spiral motion increases with the increase of the magnetic field.To solve the difficulty of extinguishing the DC arc, an active arc extinguishing method based on variable resistance for grounding electrode line was proposed here, and the arcing horn with active arc-extinguishing function was designed. The electromagnetic transient simulation model of the HVDC grounding electrode line was established, which included the modules of DC current source, overhead conductor, tower, earth electrode, lightning, arcing horn and the arc extinguishing unit. It is found through simulation calculations that when struck by lightning, the voltage and current of the arcing horn decrease along the electrode line from the converter station to the earth electrode. The impact of the lightning strikes close to the converter station is more serious than those close to the earth electrode. The absorbing energy of the arc extinguishing unit determines the arc extinguishing ability of the arcing horn, and the minimum absorbing energy that the arc extinguishing unit needs to meet is determined by the electrical characteristics of the arcing horn when struck by lightning. The grounding current has little effect on the absorbed energy of the zinc oxide valve. The valves can quickly extinguish the arc of the arcing horn. The absorbed energy is mainly the energy of the lightning. According to the simulation calculation results, the parameters of the zinc oxide valves were designed, and a new type arcing horn with active arc extinguishing function was developed. The tests showed that the preformance of the developed arcing horn meet the requirements and it can be applied to practical engineering.This work unveils the electrical and motion characteristics of the DC arc of grounding electrode line, which provide a theoretical basis for further research on DC arc. The DC arc extinguishing method proposed in this work would provide important guidance for solving the important arc extinction problem of the EHV/UHV DC grounding electrode lines.