中频真空电弧边缘击穿现象及仿真研究

Experiment and Simulation for Edge Breakdown in Intermediate Frequency Vacuum Arc

为深入掌握航空变频(360~800 Hz)电力系统中真空电器电弧特性,该文围绕中频灭弧室弧后发生的边缘击穿现象,以双温磁流体动力学仿真结合实验的研究方法,得到了以下结论:中频真空电弧离子数密度的最大值为2.6×10^(19)m^(-3),离子温度的范围为0.30~0.91eV,电子温度的范围为1.50~2.43 eV;电子与离子之间存在能量交换,电子温度的变化会引起离子温度的变化;最高离子温度出现在阳极触头边缘处,与实验发现的边缘击穿位置重合,证明了此处确实存在能量集中;中频真空电弧是超声速流体,速度在边界处减慢,根据动能热能互换原理,中频真空电弧的质量流运动规律是边缘击穿的本质原因。

The C919 aircraft is a typical more-electric aircraft equipped with an aviation variable frequency AC power system(intermediate frequency 360~800 Hz),which is also the latest development direction of power supply technology for large aircraft.In the process of localization of core components of more-electric aircraft,the current technical bottleneck is the extinguishing of intermediate frequency and high current arc of small volume aviation electrical apparatus.The application of vacuum switch is expected to solve the problem of arc extinguishing at intermediate frequency.At present,the main research methods of intermedia frequency vacuum arc include experimental observation and modeling simulation,among which modeling is an effective method to reveal the physical nature of arc discharge process.Firstly,in order to facilitate the acquisition of arc images,a short circuit experiment was carried out in the vacuum arc chamber with the shield removed.The experiment spacing was 3 mm,the diameter of the contact was 41 mm and 20 mm,and the gas pressure in the arc extinguishing chamber was 5×10^(-4) Pa.Short-circuit current forming intermediate frequency vacuum arc was generated by energy storage capacitor and inductor,with adjustable frequency of 360~800 Hz and maximum peak value of 20 kA.The intermediate frequency vacuum arc generating circuit consists of two branches:oscillation and arc initiation.Secondly,the dual-temperature magneto hydro-dynamic(MHD)model of intermediate frequency vacuum arc was established,which is based on the following assumptions:(1)The arc column region was completely ion-ized,containing only ions and electrons,without the effect of neutral particles.(2)The order of magnitude for Debye length was 10-8 m,and the order of magnitude for electron mean free path was 10^(-4) m,and the gap of contact was 3 mm.Thus,the region was quasi neutral,and the intermediate frequency vacuum arc can be equaled to MHD fluid.(3)the order of magnitude average collision time for electron and ion was 10-11 s and 10-9 s respectively.The order of magnitude of travel time for electron and ion was of 10-7 s and 10-6 s respectively.The half wave time of IF vacuum arc was 0.62~1.38 ms,thus,the solving process can be considered a steady state problem.(4)The electron was an ideal gas,so the mass flow,inertial component and viscous component are all ignored.(5)The intermediate frequency vacuum arc plasma was not in local thermodynamic equilibrium state,so the ion temperature and electron temperature need to be calculated separately.(6)The arc column region was taken as supersonic fluid,and both the anode sheath and cathode spots are taken as the boundary.The following conclusions can be drawn from the experiment and simulation analysis:(1)According to the experiment,the edge breakdown phenomenon of the intermediate frequency vacuum arc is found,and serious ablation is observed at the edge of the contact of the vacuum arc chamber,which reflected the local weak point in the insulation strength at the post-arc stage.(2)According to the simulation results of dual-temperature MHD model,the maximum ion number density of intermediate frequency vacuum arc is 2.6×10^(19)m^(-3),and the ion temperature range is 0.30~0.91 eV,and the electron temperature range is 1.50~2.43 eV.The above data is consistent with the order of magnitude of vacuum arc microscopic parameters obtained by other scholars,indicating that the calculation results of the model in this paper are correct.(3)According to the simulation results,the reason for the increase of electron temperature is Joule heat.Because of the energy exchange between electrons and ions,the change of electron temperature will cause the change of ion temperature.The highest ion temperature is found at the edge of the anode contact,which coincided with the experimental edge breakdown position,indicating that energy concentration exists here.(4)According to the simulation results,the intermediate frequency vacuum arc is supersonic flow,the velocity changes little in the arc column area,and the velocity slows down at the boundary.According to the fluid energy conversion theory,the heat energy in low-speed region is high,which indicates that the mass flow of the intermediate frequency vacuum arc plasma is the essential cause of the edge breakdown.