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     

Verification of positive streamer mechanism for negative corona Trichel pulses in O2/H2 mixtures

Current waveforms of the first negative corona pulses have been measured in O₂ + H₂ mixtures at a pressure range from 27 kPa to 50 kPa. It was observed that the hydrogen admixtures less than 4% do not change significantly the pulse current waveforms. Effects of changing cathode secondary electron emission were studied using a copper cathode coated by CuI and graphite. The results obtained support the theory of the cathode-directed streamer formation during the negative corona pulse rise.     

Frequency response characteristics of trichel pulses and the behavior of the cathode spot in a negative corona discharge

A negative corona discharge in the regime of Trichel pulses has been investigated in air at atmospheric pressure. Correlation between the behavior of the cathode spot and oscillograms of the discharge current has been revealed. The frequency response characteristics of the negative corona current have been measured as functions of voltage, tip curvature, interelectrode distance, and cathode material. It has been determined that the curvature of the tip surface in the cathode-spot localization region decisively affects the amplitude of pulses.     

The first Trichel pulse of negative corona discharge in N2 with a small admixture of SF6

Current growth waveforms of transient negative point-to-plane discharge in N₂ and in N₂ with 0·025-0·1% admixture of SF₆ at a pressure of 40 kPa have been measured and compared. The transient glow discharge regime in pure N₂ was found to be preceded by a peaked current signal of conspicuous similarity to the first Trichel pulse rise and its initial decay in N₂+SF₆ mixture. The results are in a basic agreement with a hypothesis on streamer mechanism for Trichel pulse and indicate occurrence of field emission during the rise of Trichel pulse current.     

Experimental study of pulsed corona discharge in air

We report on the results of experimental investigation of a pulsed corona discharge in electric fields with different degrees of nonuniformity under the action of a standard thunderstorm pulse in a wide range of voltages from the origination threshold to the breakdown. A high-sensitivity video camera makes it possible to record microdischarge and streamer processes in air long before the spark breakdown. It is known that the size of the corona discharge sheath increases with the supplied voltage, and the shape of the corona sheath depends on the polarity of the active electrode [1, 2]. It was demonstrated for the first time by Peek [3] that the range of voltages from the initiation of a corona discharge to the spark breakdown increases with the degree of nonuniformity of the electric field. We show that an analogous pattern is observed for a pulsed corona also. Our results show that the form of a pulsed corona discharge considerably depends on the pulse polarity, and a spark breakdown becomes possible when most branches in the streamer corona cover the electrode gap.     

Total Variation Diminishing technique in numerical simulation of Trichel corona in air

This paper deals with the numerical simulation of the Trichel pulse corona discharge in air under the room temperature and atmospheric pressure in the pin-plane configuration. A simplified drift-diffusion model of the discharge is considered with three species: electrons, positive and negative ions. The Total Variation Diminishing algorithm is used to stabilize the charge transport equations. The effect of the voltage level and the external circuit parameters on the average corona current, pulse frequency and pulse parameters are presented. The results of numerical predictions are compared with the experimental data.     

Dependence of negative ion formation on inhomogeneous electric field strength in atmospheric pressure negative corona discharge

The dependence of negative ion formation on the inhomogeneous electric field strength in atmospheric pressure negative corona discharge with point-to-plane electrodes has been described. The distribution of negative ions HO^-, NO_x ^- and CO_x ^- and their abundances on the plane electrode was obtained with a mass spectrometer. The ion distribution on the plane was divided into two regions, the center region on the needle axis and peripheral region occurring the dominant NO_x ^- and CO_x ^- ions and HO^- ion, respectively. The calculated electric field strength in inhomogeneous electric field established on the needle tip surface suggested that the abundant formation of NO_x ^- and CO_x ^- ions and HO^- ion is attributed to the high field strength at the tip apex region over 10⁸ Vm^-1 and the low field strength at the tip peripheral region of the order of 10⁷ Vm^-1, respectively. The formation of HO^-, NO_x ^- and CO_x ^- has been discussed from the standpoint of negative ion evolution based on the thermochemical reaction and the kinetic energy of electron emitted from the needle tip.     

Peculiarities of the corona discharge in air

The results of a comprehensive experimental study of the positive and negative corona discharges and their accompanying processes are reported. It is shown that specific features of the corona in air under atmospheric pressure are related to the electric wind.     

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.     

Laboratory ignition of hydrogen and carbon disulphide in the atmospheric air by positive corona discharge

Experimental attempts of ignition of sensitive explosive atmospheres by continuous positive corona discharges in coaxial electrode system were conducted in laboratory conditions. Sixty five explosions of hydrogen (H₂) and forty of carbon disulphide (CS₂) were forced. Both atmospheres were ignited by the minimum power 1–2 W, the minimum ignition current 100–130 μA at the ignition voltages 12–30 kV (for CS₂) and 16.5–25 kV (H₂). To prevent the energetic sparks, the high voltage resistor 1 MΩ was introduced in series with corona wire.     

Parametric study of radiofrequency helium discharge under atmospheric pressure

The parameters of radiofrequency helium discharge under atmospheric pressure were studied by electrical and optical measurements using high voltage probe, current probe and optical emission spectroscopy. Two discharge modes α and γ were observed within certain limits. During α to γ mode transition, a decrease in voltage (280–168 V), current (2.05–1.61 A) and phase angle (76^°–56^°) occurred. The discharge parameters such as resistance, reactance, sheath thickness, electron density, excitation temperature and gas temperature were assessed by electrical measurements using equivalent circuit model and optical emission spectroscopy. In α mode, the discharge current increased from 1.17 to 2.05 A, electron density increased from 0.19 × 10¹² to 0.47 × 10¹² cm^?3 while sheath thickness decreased from 0.40 to 0.25 mm. The excitation temperatures in the α and γ modes were 3266 and 4500 K respectively, evaluated by Boltzmann’s plot method. The estimated gas temperature increased from 335 K in the α mode to 485 K in the γ mode, suggesting that the radiofrequency atmospheric pressure helium discharge can be used for surface treatment applications.     

Surface analysis of traces stained with discharge on plane electrode in atmospheric pressure negative corona

The surface deposits of the traces stained with discharges on the brass plate electrode in atmospheric pressure DC negative corona have been analyzed. The surface analysis showed that the major deposits on the traces originate from nitrogen oxide ions NO_x^? and neutrals NO_x, or carbon clusters C_n. The relationship between the plane positions and resulting deposits obtained with the point-to-plane electrodes with arbitrary needle angle to the plane provided the information about the general behavior of negative ions NO_x^? and neutral species NO_x occurring in stationary inhomogeneous electric fields.     

Numerical simulation and experimental validation of direct current air corona discharge under atmospheric pressure

Air corona discharge is one of the critical problems associated with high-voltage equipment. Investigating the corona mechanism plays a key role in enhancing the electrical insulation performance. An improved self-consistent multi-component two-dimensional plasma hybrid model is presented for the simulation of a direct current atmospheric pressure corona discharge in air. The model is based on plasma hydrodynamic and chemical models, and includes 12 species and 26 reactions. In addition, the photoionization effect is introduced into the model. The simulation on a bar-plate electrode configuration with an inter-electrode gap of 5.0 mm is carried out. The discharge voltage– current characteristics and the current density distribution predicted by the hybrid model agree with the experimental measurements. In addition, the dynamics of volume charged species generation, discharge current waveform, current density distribution at an electrode, charge density, electron temperature, and electric field variations are investigated in detail based on the model. The results indicate that the model can contribute valuable insights into the physics of an air plasma discharge.     

Stepped form of negative corona current pulses in hydrogen

Current wave forms of initial stages of discharge formation in a short negative point-to-plane gap have been measured with a nanosecond time resolution in hydrogen at pressures (12.5–76) kPa and for various overvoltages and cathode point radii. The measurements revealed the existence of a stepped form of negative corona current pulses in hydrogen. To test existing models for negative corona pulse formation, effects of changing cathode secondary electron emission were studied using copper and brass cathodes coated by CuI and graphite. It is concluded that a negative corona pulse is associated with the ignition of a cathode-directed streamer in the vicinity of the cathode. We report what we believe are the first experimental observations of non-Trichel oscillations of negative corona current with a frequency of (1–10) MHz. This work was supported by the Scientific Grant Agency of the Ministry of Education and Academy of Sciences of Slovak Republic (Project No. 1/5190/98).     

Electrical characterization of dielectric barrier discharge driven by repetitive nanosecond pulses in atmospheric air

Dielectric barrier discharge (DBD) is an important method to produce non-thermal plasma, which has been widely used in many fields. In the paper, a repetitive nanosecond-pulse generator is used for the excitation of DBD. Output positive pulse of the generator has a rise time of about 15 ns and a full width at half maximum of 30–40 ns, and pulse repetition frequency varies from single shot to 2 kHz. The purpose of this paper is to experiment the electrical characteristics of DBD driven by repetitive nanosecond pulses. The variables affecting discharge conditions, including air gap spacing, dielectric thickness, barrier fashion, and applied pulse repetition frequency, are investigated. The relationship between electric field, discharge current, instantaneous discharge power across air gap, and estimated electron density with the length of air gap, dielectric thickness, barrier fashion, and pulse repetition frequency is obtained respectively, and the experimental results are also discussed. In addition, two typical images exhibiting homogeneous and filamentary discharges are given with different experimental conditions.     

Numerical simulation and experimental validation of a direct current air corona discharge under atmospheric pressure

Air corona discharge is one of the critical problems associated with high-voltage equipment. Investigating the corona mechanism plays a key role in enhancing the electrical insulation performance. An improved self-consistent multi-component two-dimensional plasma hybrid model is presented for the simulation of a direct current atmospheric pressure corona discharge in air. The model is based on plasma hydrodynamic and chemical models, and includes 12 species and 26 reactions. In addition, the photoionization effect is introduced into the model. The simulation on a bar-plate electrode configuration with an inter-electrode gap of 5.0 mm is carried out. The discharge voltage-current characteristics and the current density distribution predicted by the hybrid model agree with the experimental measurements. In addition, the dynamics of volume charged species generation, discharge current waveform, current density distribution at an electrode, charge density, electron temperature, and electric field variations are investigated in detail based on the model. The results indicate that the model can contribute valuable insights into the physics of an air plasma discharge.     

Theoretical investigation of ozone production in negative corona discharge

The purpose of this work is to highlight the chemical kinetics in plasma of pure oxygen. A comprehensive model of ozone generation in wire-to-cylinder negative corona discharge is presented. The model combines the physical processes in the discharge with the chemistry of ozone formation. It is based on an extensive reaction scheme including the major electronic and ionic processes. The importance of excited atomic and molecular states is demonstrated. The obtained results show clearly that the surface material affect quite well the ozone decomposition.     

Numerical simulation of stationary negative corona in air

A negative corona in air is numerically simulated for the coaxial cylindrical geometry of electrodes. The goal of the investigation is to gain insight into physical processes and physical conditions in the gap that favor the corona-arc transition. An experiment aimed at contrasting calculated and real characteristics is described.