正极性电晕放电脉冲特性仿真研究

Simulation Study on Pulse of Positive Corona Discharge

正极性电晕放电脉冲由于其幅值较大,持续时间较长,在特高压交直流输电线路无线电干扰产生中占主导地位。为了深入研究正极性电晕脉冲发展的微观物理过程及其重复机制,文中基于流体动力学模型,用背景电离来代替光电离为正极性流注的发展提供种电子,对间距为1 cm,施加电压为17.5 k V的同轴电极进行了正极性电晕放电特性仿真,得到了一组较为规则的正极性电晕电流脉冲,脉冲幅值为15～25 mA。而后对初始脉冲不同发展阶段的空间电场分布特性和3种带电粒子(正离子、电子和负离子)空间浓度分布特性进行了分析讨论,对死区时间内的电场和正离子空间演化特性进行了描述,并给出了新的脉冲发展时空间电场分布。通过仿真发现,正流注在向前发展时,等离子体通道内的场强非常小,而流注头部场强较大。流注停止发展,逐渐消散时,通道内和流注头部的正离子在电场力的作用下向外迁移,导线表面电场逐渐恢复,当恢复至可以引发初始电子崩的起晕场强时,新的电晕脉冲发生。

Due to the large amplitude and long duration,the positive corona discharge pulses play a dominant role in radio interference performance of UHV AC or DC transmission lines.In order to study the micro physical process and repetitive mechanism of positive pulses more deeply,the positive corona discharge pulses in air are numerically simulated in this paper based on the hydrodynamic drift-diffusion model,where the seed electrons are supplied by background ionization instead of the photoionization process.The simulation is performed in a coaxial wire-cylinder electrode with an inter-electrode gap of 1cm and a voltage of 17.5 kV,and the amplitude of positive pulse between 15 mA and 30 m A.Then the distributions of electric field(E-field)and three ionic species densities(positive ions,negative ions and electrons)along the gap at different stages of the first current pulse are discussed.Further the influence of positive ion movement on E-field distribution in dead time is analyzed in details.Moreover,the distribution of E-field around the second positive current pulse is also presented.It is observed that the positive streamer propagation velocity has fallen when the streamer head are moving away from anode.After the streamer terminated,the streamer channel begins to decay.Due to the E-field force,the positive ions diffuse away from anode while the conductor surface E-field strength recovers gradually.Until the strength reach the threshold value for avalanche ionization the next new pulse occurs.