Current analysis of DC negative corona discharge in a wire-cylinder configuration at high ambient temperatures

To study the characteristics of DC negative corona discharge in a wire-cylinder configuration at an ambient temperature range of 350–850 °C, the I–V characteristics and the current composition are analyzed under different conditions. A simple method is proposed to determine the DC corona onset threshold voltage. At high ambient temperatures, in the DC negative corona discharge gap, some electrons are not attached to the electronegative gas molecules and move to the anode tube. Thus, these electrons form an electron current, which may account for most of the total discharging current. The ratio of the electron current to the total discharging current increases with increasing temperature. In a mixture of O₂ and N₂ and a mixture of CO₂ and N₂, the ratio of electron current increases with increasing N₂ content in the mixtures. The cathode material has little influence on the corona discharge characteristics at high ambient temperatures.     

气体介质对多间隙气体开关电晕均压与自击穿特性的影响

快脉冲直线变压器型驱动源(FLTD)是近年来快速发展的新型脉冲功率源技术,多采用多间隙气体开关作为开关器件。电晕均压措施有利于提升开关击穿性能,但不同气体中电晕放电有显著区别。本文首先研究了空气中针电极对单间隙电晕放电特性的影响,确定了电晕针电极的尺寸,之后研究了N2,CO2,SF6/N2混合气体、C4F7N/N2混合气体中的电晕放电特性,研究了电晕均压6间隙气体开关击穿电压及其稳定性随气体种类和气压的变化规律。实验结果表明,N2中电晕电流较大且不稳定,空气中电晕电流比N2中低,且电晕放电较为稳定,微量强电负性气体加入会极大降低电晕放电电流。当采用空气和N2作绝缘介质时,气体开关击穿电压随气压升高线性增加,但存在低值击穿,微量强电负性气体混合N2可显著提升击穿电压的稳定性。1%SF6/99%N2混合气体在0.18 MPa时,击穿电压约为197.33 kV,标准偏差占击穿电压比例为1.50%,1%C4F7N/99%N2混合气体在0.15 MPa时,击穿电压约为190.42 kV,标准偏差为0.55%。这表明,微量环保替代气体C4F7N与N2的混合气体对于提升多间隙气体开关击穿电压稳定性有显著作用。     

发射光谱研究多针对板电晕放电O活性原子特性

利用发射光谱技术在大气压下测量了空气中多针对板负直流电晕放电和正电晕流光放电产生的O(3p5 P→3s 5 S02777.4nm)活性原子发射光谱。在负电晕放电中,研究了放电功率、电极间距、N2含量和相对湿度等因素对O活性原子产生过程的影响;在正电晕流光放电阶段,研究了O活性原子相对密度在放电反应空间的分布特点。结果表明:O活性原子产量随放电功率的增加而增大,随电极间距增大而减少,随相对湿度和氮气含量的增加,其产量先增大后减少;O活性原子相对密度沿针尖轴向呈先增大后减小的趋势。     

A study of cross-gas-flow to stabilize an atmospheric pressure glow plasma in a multi-pin-to-multi-cupped-plane negative corona discharge

In a multi-pin-to-multi-cupped-plane DC negative corona discharge configuration, a stable and diffuse glow discharge controlled by a fast airflow was obtained. This paper investigates the effect of the air gas flow velocity and the electrode structure on the discharge mode transition and the stabilization of the glow discharge by means of electric measurements and emission records. The stabilization mechanism of the glow discharge is discussed. The maximum glow discharge current reached 3.9 mA and the average current density was about 0.7 mA/cm².     

Impulse breakdown characteristics of the plane-to-plane electrode system with a needle-shaped protrusion in SF6

This paper presents the impulse pre-breakdown and breakdown characteristics of the plane-to-plane electrode system with a needle-shaped protrusion in SF₆ gas. The breakdown voltage–time (V–t) characteristics and the breakdown voltage–gas pressure (V–p) characteristics of a highly non-uniform SF₆ gas gap under positive and negative lightning impulse voltages are investigated in the pressure range between 0.1 and 0.5 MPa. The pre-breakdown developments are examined by the corona current and light emission measurements with high time resolution. As a result, the dielectric strengths versus time-to-breakdown of SF₆ gas gap under positive lightning impulse voltages were nearly independent of the gas pressure. The first streamer corona was initiated at the tip of the needle electrode, and the streamer corona pulses developed with a stepwise propagation. The discharge paths were zigzag, and the branches of the discharge channel for positive polarity were created. On the other hand, the leader channel in the negative polarity was thicker and brighter than that in the positive polarity.     

棒-板电极直流负电晕放电特里切尔脉冲的微观过程分析

本文基于流体动力学理论改进出一种新的棒-板电极负电晕放电混合数值模型, 模型中加入了27种主要碰撞反应, 并考虑了光电离和二次电子发射过程. 对棒-板间距3.3 mm, 施加电压-5.0 kV情况下进行数值计算, 得到负电晕放电的特里切尔脉冲. 重点分析了单个特里切尔脉冲持续过程中5个关键时刻的微观特征量发展规律, 丰富并量化描述了特里切尔脉冲的微观过程, 主要结论如下: 随着放电时间的发展, 电场集中分布区域向阳极移动且幅值变小, 这对电子崩的发展非常不利. 大部分放电区域都是电中性的, 只有在阴极鞘和阳极鞘附近有带正电的等离子体特性, 带负电的离子云随着放电时间的发展缓慢向阳极发散式移动. 整个特里切尔脉冲持续过程中, 阴极鞘内电子密度几乎为0; 特里切尔脉冲前期, 阴极鞘附近电子密度迅速增加至最大值并保持基本不变; 随着放电时间的增加, 放电间隙内电子密度整体增加, 并且向阳极发展. 在特里切尔脉冲后期, 电子的产生主要来自于N₂和O₂的碰撞电离, 电子的消失则主要由N₂⁺的复合决定, O₄⁺和O₂^-分别是数量最多的正离子和负离子. 关键词： 负电晕 混合模型 特里切尔脉冲 微观特征量     

An experimental study of relative humidity and air flow effects on positive and negative corona discharges in a corona-needle charger

In this paper, the effects of inlet air RH and air flow rate on positive and negative corona discharges in a corona-needle charger have been experimentally studied and discussed. Its corona discharge characterizations in terms of current-to-voltage relationships of the corona-needle charger on the effects of inlet air RH and air flow rate were evaluated at applied corona voltages between 0 and 3.1 kV, an air flow rates between 5 and 15 L/min, a relative humidity between 20 and 90%, and an operating pressure of about 101.3 kPa. Experimental results were shown that discharge current is strongly affected by the RH level of the inlet air. The positive discharge current was found to be decreased with increasing RH value at RH values below 60% and increased with increasing RH value at RH value above 60% in the same corona voltage. The negative discharge current was found to be stable with increasing RH value at RH values below 40% and increased with increasing RH value at RH value above 40% in the same corona voltage. For the air flow rate effects, the positive discharge current was found to slightly decrease when the air flow rate increased at RH value below 90% and to increase with the air flow rate at RH value of 90%. For the negative corona, the discharge current was also found to monotonically decrease when the air flow rate increased.     

Negative corona discharge from a water droplet under the pulsating DC field

Corona discharge from a fine water droplet always involves deformation of the droplet shape or Taylor-cone formation, emission of fine water jets or disruption of droplet. Therefore, corona discharge from a water droplet always manifests complicated aspects. In addition, disruption of Taylor cone simultaneously affects not only discharge current but also motion of water droplet. To confirm corona discharge phenomena from a water droplet protruded from a tip of a metal capillary tube with a diameter of 1 mm, negative corona discharge was investigated by using a water droplet located at a tip of grounded rod electrode facing a ring electrode with positive dc voltage superimposed by ac one. Since the droplet has inherent resonant vibrating frequency defined by the size or volume, the volume of water droplet was adjusted at 20 nL where the corresponding resonant frequency was 500 Hz. The period of the event of successive corona discharge is exactly consistent with resonant frequency defined by the size of the water droplet. As a result, corona pulse trains with a definite duration appeared intermittently corresponding to its resonant vibration. When dc voltage superimposed by ac voltage with resonant frequency of 500 Hz was applied to the water droplet, corona pulse trains appeared at the period corresponding to the frequency. The maximum value of corona current reasonably increased with the applied voltage. Even when the frequency of ac field superimposed on dc field was varied from the resonant frequency, corona pulse trains occur corresponding to not only the superimposed field frequency but also resonant frequency.     

An approach for unipolar corona discharge in N2/O2 gas mixture by considering townsend conditions

In this study (α/p) = f(E/p) functional relation is derived for the gas mixture of N₂/O₂ by considering Townsend approach, and formation mechanism of corona discharge is investigated for the coaxial electrode system located in this gas medium. The electron energy distribution function (EEDF) which is required for estimation of ionization coefficient, is determined by considering probability distribution function of inelastic electron collisions versus energy. An algorithm for determining ionization coefficient for binary gas mixture is presented. The development and motion of the electron avalanche in inter-electrode gap are studied by considering the effect of positive space charges. It is determined by considering the derived mathematical expressions that the formation of corona discharge is related with the variation of the current characteristics in inter-electrode gaps depending on the change of potential of central electrode.     

A simple model of processes in the drift region of negative corona discharge in a mixture of air with halocarbons

A model for negative glow corona discharge in a coaxial electrode configuration is presented. The main goal of this model is to describe the influence of a more efficiently electron-attaching gas on the distribution of free electron density in the drift region. The calculated distributions of electrons and other ionic components are shown. The model was applied in experiments realized in air + freon mixtures. A qualitative agreement between theoretical and experimental results was achieved.     

Formation Mechanism of the So-Called Corona Figure

A dense radial array of chromium microneedles is formed on a field-emission cathode interacting with a negative corona discharge in ambient Cr(CO)6 of the order of 10-2 torr. The article discusses physical and chemical processes which underlie the formation of this so-called corona figure, based on extensive electron microscope observations. The overall shape of a corona figure is a function of the substrate geometry, indicating that field electrons emitted from the substrate play a vital role in nucleating the figure. A negative electric field curves the growth direction of the needles that compose the figure, and a high magnetic fileld applied externally well aligns them along magnetic-field lines. These facts support strongly the hypothesis that the figure is formed as the electron avalanches, originating at the substrate, propagate outward. The technical term "field-emission corona" is proposed for the present corona discharge, because the discharge is initiated and sustained by field-emitted electrons.     

喷嘴-平板直流电晕放电中的OH(A2S+→X2P, 0-0)光谱研究

 为更深入地认识电晕放电低温等离子体中自由基的生成机理，以发射光谱测量为基础并结合背景气体淬灭率影响，研究了常压下喷嘴-平板电晕自由基簇射过程中放电参数、背景气体、电极气成分等因素对OH(A²S⁺→X²p, 0-0)发光的影响。结果表明：在放电参数影响中，放电电压及放电电流都会影响OH生成量，OH发光随功率增加而大大增强；在加湿氮气直流电晕放电中有明显的OH(A²S⁺→X²p, 0-0)光谱存在，但加湿空气条件下OH生成较少；载气增湿后OH生成量明显增多，而Ar和O­2的存在分别增强和减弱了OH(A²S⁺→X²p, 0-0)发光，可能的原因是这两种物质影响了放电和OH(A²S⁺)的淬灭。     

Influence of the corona-wire diameter and length on corona discharge characteristics of a cylindrical tri-axial charger

In this paper, the corona discharge characterization in terms of current–voltage relationships of a unipolar cylindrical tri-axial charger on the effects of the corona wire diameter and length have been experimentally studied and discussed. A commercial computational fluid dynamics software package, COMSOL Multiphysics™, was used to predict the electric field distribution in the ion generation and charging zones of the charger and the ion penetration through the perforated screen opening on the inner electrode of the charger. It was found from experimental results that both positive and negative charging currents in the charging zone of the charger increased with increasing corona and ion-driving voltages. At the same corona and ion-driving voltages, both positive and negative coronas were decreased with increasing diameter of the corona-wire. Compared with the corona-wire of 22 mm in length, the magnitude of both positive and negative charging currents were markedly higher for corona-wire of 11 mm in length at the same corona voltage. It was found that the charging currents for negative coronas were about 1.2 times higher than those positive coronas at the same corona and ion-driving voltages. Numerical results of the electric field distribution and the ion and charged particles migrations in the discharge and charging zones of the charger is correlated to have the same direction with the experimental results of the current–voltage relationships. Also, this can be used to guidance in describing the electric field distribution and the behavior of ion and charged particle trajectories that cannot be seen from experiments in order to improve the applicably design and refinement of a unipolar cylindrical tri-axial charger.     

Characteristics of DC discharge in a wire-cylinder configuration at high ambient temperatures

In the present work, the characteristics of direct-current (DC) discharge in a wire-cylinder configuration at an ambient temperature range of 350–850 °C were studied by analyzing photographs of the discharging process and the corresponding V–I characteristics, with the aim of facilitating the application of plasma technology in the fields of energy and the environment. The influences of the ambient temperature, the inter-electrode gap, the gas medium and the cathode material on the DC discharge were investigated. The corona-onset threshold voltage (COTV) and the spark-breakdown threshold voltage (SBTV) decrease as the ambient temperature increases, and the SBTV decreases more rapidly. Increasing the inter-electrode gap enlarges the difference between the SBTV and the COTV. After spark breakdown, in an air atmosphere, glow discharge is more likely to take place under conditions of high ambient temperatures or small inter-electrode gaps. The values of the SBTV in different atmospheres have the following relation: air ≈ O₂ > CO₂. At an ambient temperature range of 350–850 °C and in an atmosphere of N₂, glow discharge and arc discharge occur successively as the output voltage of the power supply is increased, while in an atmosphere of O₂ and CO₂, only corona and arc discharge are successively observed. In an air atmosphere, when the inter-electrode gap is 29 mm, corona, glow and arc discharge occur successively with increasing output voltage when the ambient temperature is 850 °C, while only corona and arc discharge appear when the temperature is 350–750 °C. When the inter-electrode gap is 5 mm in an air atmosphere, corona, glow and arc discharge occur successively in an ambient temperature range of 350–850 °C. The cathode material has a minor influence on the COTV and a more significant influence on the SBTV. In a device using a cathode with a low work function, the SBTV is low, and the power to maintain arc discharge is small.     

直流大气压电晕放电电子密度的光谱研究

利用自制针—板式放电装置,在大气中进行电晕放电实验。用发光区域照片光斑的大小,讨论了电晕层厚度与电源电压的关系。在相同针板间距下,电晕层厚度随着电压的升高而增大;在相同电压下,电晕层厚度随着针板间距的增大而减小。由于高能电子密度能够通过氮分子第二正带系337.1 nm的光谱强度大小反映,因此对氮分子第二正带系337.1 nm谱线的强度用发射光谱法进行了测量。实验结果发现在针尖附近高能电子密度最大,并且高能电子密度随电压的升高而增大;电压一定时,高能电子密度随针板间距的增大而减小。在针板间距和电源电压不变的情况下,高能电子密度随针尖曲率半径的减小而增大。     

Corona discharge processes

Applications of corona discharge induced plasmas and unipolar ions are reviewed. Corona process applications emphasize one of two aspects of the discharge: the ions produced or the energetic electrons producing the plasma. The ion identities depend on the polarity of the discharge and the characteristics of the gas mixture, specifically on the electron attaching species. The electron energies depend on the gas characteristics and on the method of generating the corona. In general, in an application using ions, the corona induced plasma zone will occupy a small fraction of the total process volume, while a process using the electrons will fill most of the volume with the plasma. Current state-of-the knowledge of ionized environments and the function of corona discharge processes are discussed in detail     

发射光谱研究多针对板正电晕放电形貌

利用光学发射光谱(OES)法检测N₂发射光谱,研究了常压下多针对板正电晕放电中辉光放电和击穿流光放电的高能电子分布,并与相同电极结构下负电晕放电进行了比较。根据N₂第二正态激发谱峰I_SPB在空间的分布,较精确地确定了辉光放电电离区形貌和击穿流光放电电通道形貌,体积分辉光放电中I_SPB获知I_SPB与放电电流I之间的关系。辉光放电中,电离区范围和I_SPB比负电晕放电小,电子雪崩沿针径向比沿轴向发展范围大;随着U升高,电离区范围只沿针轴向小幅度增大;I_SPB的积分值与I近似成二阶线性关系。击穿流光放电中,针板之间形成放电通道;针尖周围I_SPB较强的区域成“子弹状”,距离针尖较远的放电通道内高能电子密度沿针轴向分布比较均匀,沿针径向先略有增大后减小。     

An analytical method for DC negative corona discharge in a wire-cylinder device at high temperatures

This paper proposes an analytical solution for DC negative corona discharge in a wire-cylinder device based on experimental results in which both the corona and drift regions are considered; this approach aims to provide a theoretical method for analyzing electrostatic precipitation at high temperatures. The inter-electrode space is divided into three zones, namely, the ionization layer, the attachment layer (corona region) and the drift region, to investigate the space charge concentration and the electric field distribution. The boundary of the ionization layer is assumed to be the radius at which the rate of ionization balances that of electron attachment. The radius where the value of E/N equals 110 Td is recommended as the boundary of the attachment layer. It was determined that an increasing temperature leads to a decrease in the largest space charge number density and the largest electric field in the drift region that can be provided by a discharging device. With respect to the device in the present work, when the temperature increases from 350 °C to 850 °C, the largest electric field decreases from ∼9 × 10⁶ V/m to ∼3 × 10⁶ V/m, and the largest charge number density decreases from ∼1.3 × 10¹⁵ m⁻³ to 6.4 × 10¹⁴ m⁻³. The radius of the corona region, the space charge number density and the electric field increase as the applied voltage increases at a given temperature. For example, at a temperature of 550 °C, when the applied voltage increases from 10,500 V to 18,879 V, the radius of the corona region increases from ∼2.9 mm to ∼4.9 mm. It appears to be unreasonable to use a constant value that is calculated from Peek's formula as the electric field at the surface of the cathode under all of the conditions.     

The Use of Corona Discharge for Rubber Crush Drier Exhaust Control

The rubber crush drier exhaust contains mainly styrene, ethylbenzene, cumene, diizopropylbenzene, alkylphenols, monocyclic terpenes and technological additives as stearic acid, oils an colophony. For possible application of d.c. corona discharge to control styrene in exhaust, the reaction of styrene with additives and air in various d.c. corona discharge tubes was studied. The change of styrene content in the gas phase was measured by IR absorption spectrometry. The decrease of styrene concentration was minimum 83% and reached the 98,9% efficiency. No aromatic compounds remain after corona discharge action in gas phase. The structure of solid products was specified with reflection IR absorption spectrometry and compared with a calibration polystyrene foil (300 μm). The main product has been of malein anhydride-styrene copolymer character for a negative corona discharge and of phenol or quinone-styrene copolymer character for a positive corona discharge.     

环形电极单间隙电晕放电伏安特性

基于用于直线变压器型驱动源的多间隙气体开关结构,提出一种环形放电间隙与电晕针并联的气体火花间隙。通过测量间隙耐压过程中电晕放电的伏安特性,研究了气体介质、气压、电晕极性、电晕针长度以及针尖对应电极结构等因素对伏安特性的影响。结果表明:以空气为绝缘气体,负极性电晕可获得较稳定的伏安特性;改变电晕针长度和针尖对应电极结构可方便地实现对电晕放电伏安特性的调节以满足开关要求。