交直流电场共同作用下电极起晕特性及气压影响的机理研究

The corona inception field of the electrode is one of the key limiting parameters that restricts the design and operation of the transmission line, shielding electrode of the DC converter valve. In plain and high altitude areas, ac and dc electric field may appear simultaneously on the surface of the electrodes in the case of AC and DC transmission lines constructed in the same tower or the shielding electrode of the DC converter valves. Under the joint effects of the time-varying electric field and air pressure, the corona inception characteristics of the electrode are obviously different from those in the past. Therefore, it is necessary to investigate and reveal the influencing mechanism. The proposed project mainly studies: (1) the space-time distribution of space charge and the space charge field under the combined action of AC and DC electric field; (2) the corona inception characteristics of the very uneven field- electrodes and slightly uneven field- electrodes, the modeling method will also be investigated; (3) the influencing mechanism of air pressure on the corona inception characteristics of the electrodes under the action of combined AC and DC electric fields, the modeling method will also be investigated. Through the research, the corona inception mechanism of the electrodes under the action of combined AC and DC electric fields together with the air pressure effects will be revealed. The electric inception threshold of the high-voltage electrodes and the influencing parameters will be acquired. This research project will make a breakthrough in the mechanism of the corona inception mechanism of the electrodes under the action of combined AC and DC electric fields together with the air pressure effects. It will also provide a significant theoretical support for the design, construction, and operation of super, ultra high voltage transmission and transformation projects.

电极的起晕场强是制约输电线路、直流换流阀屏蔽电极设计和运行的关键限制参数之一。在平原和高海拔地区，同塔架设的交直流输电线路、直流换流阀屏蔽电极表面均有可能出现交直流电场的共同作用。在时变的电场和气压的共同影响下，电极的电晕起始特性和以往的情况有明显区别，亟需探究并揭示其影响机理。本项目主要研究：（1）交直流电场共同作用下，空间电荷的时、空分布和空间电荷场的规律；（2）交直流电场共同作用下，极不均匀场、稍不均匀场电极的起晕特性及建模计算方法；（3）气压对交直流电场共同作用下电极起晕特性的影响规律及建模计算方法。通过研究，可以揭示电极在交直流电场共同作用下的电晕起始机理及气压影响的科学规律，获得高压电极起晕场强的阈值及参数的影响规律。课题将在交直流电场共同作用下电极起晕特性及气压影响的机理上有所突破，为超、特高压输变电工程的设计、建设、运行提供重要理论支撑。

在平原和高海拔地区，同塔架设的交直流输电线路、直流换流阀屏蔽电极表面均有可能出现交直流电场的共同作用。在时变的电场和气压的共同影响下，电极的电晕起始特性和以往的情况有明显区别，亟需探究并揭示其影响机理。本项目开展的研究工作和成果如下： .1）设计了低电位条件下用于检测交直流电场作用下高压电极电晕起始电压、电晕起始电流脉冲的四通道同步采集系统，可以安全、准确地获得电极电晕起始的时域特性。.2）建立了交直流电场共同作用下电极电晕放电的流体模型，包括电子、正离子、负离子的连续性方程和电位的泊松方程；采用了流线扩散算法，添加各向异性流线人工扩散项，解决了对流项占主导的流体动力学方程求解时数值震荡的难题，获得了电晕起始时空间电荷的时空分布特性。.3）获得了交直流电场共同作用下棒—板、线—板、小曲率电极的电晕起始特性。在相同固定电压分量下，电极起晕所需要的变化电压分量从大到小依次为直流侧正极性，直流侧负极性，交流侧正半周，交流侧负半周。对于棒—板和线—板电极，直流分量占比一定时，由于空间正离子的作用，可以表现出不同程度的电晕抑制效应。对于小曲率电极，随着交流分量的增大，增大电极间距对抑制电晕起始的效果减弱；当顶端倒角处存在粗糙结构缺陷时，增大电极之间的间距对抑制电晕起始的效果比增大倒角半径更加明显。.4）获得了交直流电场共同作用下，气压对电晕起始特性的影响规律。电晕起始电压随气压的降低和外加直流分量的增加而减小。低气压条件下，直流分量越小，对空间电荷积聚的影响越小；交流分量的存在对空间电荷产生不可忽视的影响，即使是很小的交流分量，与只有一种直流分量的情况相比，电晕起始特性也会出现明显的差异。.通过本项目的研究研究，揭示了电极在交直流电场共同作用下的电晕起始机理及气压影响的科学规律，为超、特高压输变电工程的设计、建设、运行提供重要理论支撑。