甲烷/空气混合气体在针板电极下的微间隙放电特性

doi:10.19595/j.cnki.1000-6753.tces.220560

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摘要

研究爆炸性环境下微间隙放电过程及特性对本质安全电路的研究具有指导性意义,但目前爆炸性环境下的微间隙放电特性尚不明晰,且大多从宏观角度进行研究,缺少微观层面的理论分析,该文根据程控微间隙放电实验装置的电极结构,基于流体动力学理论模拟研究了甲烷—空气混合气体在低电压微间隙放电动态过程。通过改变极距、甲烷空气混合气体浓度的变化来分析对电子密度、各正离子数密度、电场强度和平均电子能量的影响,从微观层面分析了微间隙放电机理,并通过试验验证了仿真结果的真实性和可靠性。经研究发现：阴极板附近的正离子鞘层区使得阴极板场强发射发生畸变,畸变为原来的3~5 倍,电场强度大于场致发射所需临界电场强度,放电过程中存在场致发射;甲烷体积分数在3.5%~13.5%范围变化时,体积分数每增加5%,CH₄⁺数密度增加约2×101 5 m^-3;当针板距离小于10 μm 时,电场畸变较大,满足场致发射条件,汤森放电和场致发射共同存在,平均电子能量上升两次;大于或等于10 μm 时,电场强度畸变程度变弱,低于场致发射电场强度临界值,放电机制为汤森放电,平均电子能量只上升一次。

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	王党树
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关键词 ：爆炸性环境, 针板电极, 流体动力学理论, 微间隙放电

Abstract：

Electrical equipment working in explosive environment should meet the requirements of intrinsic safety. Domestic and foreign scholars evaluate the intrinsic safety based on the voltage and current characteristic curves of the discharge measured by IEC-SSTA spark test device. However, the discharge mechanism and particle change law in case of equipment failure are not clear. In the design of intrinsically safe electrical equipment, there will be transition explosion-proof, which limits the improvement of intrinsically safe output power, resulting in that the output power of intrinsically safe equipment can only reach about 20 W.Therefore, based on the electrode structure of the program-controlled micro-nano discharge test device, the discharge physical model is established in the methane-air mixture environment. The discharge parameters such as axial electron density, various positive ion density and so on are obtained by two-dimensional modeling and simulation of the discharge through hydrodynamics, thus clarifying the discharge mechanism of plasma micro-gap.
Firstly, a two-dimensional discharge model is established based on the electrode structure, and the boundary conditions are set. Secondly, add the chemical reaction equation and set the conditions such as the cross section data involved in the reaction. Then, set the initial gas concentration and particle density. Finally, the simulation is carried out to obtain the data by changing the electrode distance and the concentration of methane-air mixture. According to the simulation, the influence of the change on the electron density, the number density of positive ions, the electric field strength and the average electron energy is analyzed, and the micro-gap discharge mechanism is analyzed from the microscopic level.
At the initial stage of discharge, the degree of electron collision ionization reaction between the electrons in the electrode gap and other gas molecules is relatively low, and the electron density is in a slow rising stage. As the energy gained by the electrons in the electric field increases, the collision ionization becomes more and more intense, and the electron density increases rapidly. With the development of motion, the probability of recombination of electrons and positive ions also increases, which slows the growth of electron density. In general, the electron density first increased to the peak and then decreased, and the discharge continued to develop and gradually entered a stable stage. Then change the pole spacing to get the conclusion that the pin-plate spacing not only affects the particle impact ionization degree, but also affects the discharge mechanism. When the needle plate spacing is greater than or equal to 10 μm, there is no field emission in the discharge process. After changing the concentration of methane, it can be concluded that the contribution rate of O2 and CH4 to the discharge is greater than that of N2, and the discharge is mainly the collision ionization of O2 and CH4. Finally, experimental verification is carried out. The experimental results are consistent with the simulation results, which verify the correctness of the theoretical analysis.
The following conclusions can be drawn from the simulation analysis: (1)During micro-gap discharge, sheath area will be formed at about 2 μm of the positive electrode and about 0.5 μm of the negative electrode. The positive ion sheath area near the cathode plate distorts the field intensity emission of the cathode plate. (2)When the methane concentration changes from 3.5% to 13.5%, the number density of N₂ ⁺ is relatively stable about 4×10¹⁵ m^{- 3}, the number density of O₂ ⁺increases with increasing methane concentration when methane concentration is less than 8.5%. When the methane concentration is greater than or equal to 8.5%, the O₂ collision ionization in the mixed gas reaches saturation and does not increase with the increase of methane concentration. (3) The change of electrode distance affects the electric field intensity between electrodes and the discharge mechanism.

Key words： Explosive environment needle plate electrode hydrodynamic method micro gap discharge

收稿日期: 2022-04-08

PACS:

O461

基金资助:

国家自然科学基金面上项目（51776177）和国家自然基金科学青年项目（51604217）资助

通讯作者: 王党树男,1976 年生,副教授,研究方向为电力电子技术。E-mail：wangdangshu@126.com

作者简介: 邓翾女,1997 年生,硕士研究生,研究方向为电力电子技术。E-mail：1030390582@qq.com

引用本文:

王党树, 邓翾, 刘树林, 仪家安, 王新霞. 甲烷/空气混合气体在针板电极下的微间隙放电特性[J]. 电工技术学报, 0, (): 230642-230642. Wang Dangshu, Deng Xuan, Liu Shulin, Yi Jia'an, Wang Xinxia. Microgap Discharge Characteristics of Methane/Air under the Needle Plate Electrode. Transactions of China Electrotechnical Society, 0, (): 230642-230642.

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https://dgjsxb.ces-transaction.com/CN/10.19595/j.cnki.1000-6753.tces.220560 https://dgjsxb.ces-transaction.com/CN/Y0/V/I/230642

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