DC corona discharge from a wire particle floated with a microgap in parallel plate electrodes

Conductive particles existing in a high-voltage system could deteriorate the system performance owing to an electric discharge via the particles. In case when the particles exist in a dc high-voltage electrode system, the location of the particle would inevitably affect the discharge aspect. A corona-onset and breakdown voltage from a metallic wire particle were measured in detail. The wire particle has a length ranging from 6 to 12 mm, and a diameter of 0.25 mm. It was fixed between a parallel plate electrode with a spacing of 20 or 30 mm. When the particle was close to the negative electrode, a corona discharge occurred stably, and the corona-onset voltage was increased as the gap length between the negative electrode, and the positive end of the particle increased up to 0.8 mm. In contrast, when the particle was close to the positive electrode, the breakdown always occurred without preceding the corona discharge. At the middle region between the electrodes, the corona onset occurred at almost constant voltage.     

Bipolar DC corona discharge from a floating filamentary metalparticle

The motion of a filamentary particle and also the discharge from a particle have been extensively investigated for the development of a prevention and protection method against breakdown in gas-insulated switchgear. The particle showed several different patterns of motion, e.g., "standing," precession motion, oscillating up and down, etc. Each of these types of motion depends on corona discharge from the particle itself. Since this motion cannot be explained only by monopolar discharge from one end of a particle, bipolar discharge from both ends of a particle occurring simultaneously has been investigated by applying the floating particle method. The particle length and the gap between the particle and electrode were chosen as parameters. From experimental results, several interesting features were obtained. The curve of bipolar corona. current lies between negative and positive corona currents of monopolar curves. There is a sudden current increase at the threshold voltage that seems to be a new feature of the corona current from a filamentary particle. So far, the experimental results indicate that this threshold voltage is not a function of particle length, but it could depend slightly on length. Flashover voltage is a function of particle length and the gap. It decreases with length and increases with the gap     

Triangle-shaped DC corona discharge device for moleculardecomposition

An earlier point-to-plane geometry corona device with a rectangular cross section demonstrated low decomposition efficiencies. The numerical simulation of this device suggested that three were zones of low electron density and electric field significant decrease in resulting in electrical sneakage which caused a significant decrease in the kinetic rate coefficients in the chemical reaction process. A triangle-shaped DC corona discharge device was developed to improve the electrical sneakage problem, and a semiempirical mathematical model was developed to describe the detailed electrical characteristics and to refine estimates on the optimum shape of the device. The preliminary experimental results indicated that the decomposition efficiency was much improved     

Effect of a DC corona electrical discharge on the airflow along a flat plate

Ability of a DC electrical discharge to control low-velocity airflow along a flat plate is analyzed. Specifically, the electrodes are flush mounted on the insulating surface of the plate creating a tangential corona discharge at close vicinity of the wall. In this paper, visualizations of the low-velocity airflow (up to 1.4 m/s corresponding to Re=16 000) along the flat plate are presented. They show that the ionic wind induced by the corona discharge modifies the original airflow considerably, resulting in the airflow reattachment to the wall and reduction of the wake size. Velocity measurements by particle imaging velocimetry and by Pitot tube are conducted in a wind-tunnel loop for higher airflow velocities (up to 11 m/s corresponding to Re=117 800). Results show that the corona discharge at such high airflow velocities does affect significantly the velocity profile within the viscous boundary layer.     

Modeling of DC corona discharge along an electrically conductiveflat plate with gas flow

The development of a corona discharge was evaluated numerically over a finite region of a semi-infinite flat plate having small (ohmic) surface conductivity with flowing gas. The model simulates a positive ion corona discharge (ionic wind) in the direction of gas flow generated by two parallel wires mounted flush with the surface of the plate. The deposition and removal of ions at the surface are permitted. Five coupled partial differential equations govern the gas phase model together with empirical equations for electrical discharge (Φ-I characteristic). Two voltage bias case studies were considered: first, the two electrodes have the same potential but are of opposite sign; and second, the positive electrode carries the full potential with the remaining electrode grounded. Several interesting effects are noted relating to the voltage and current distribution, surface potential, and free-stream velocity. Boundary layer development and surface shear are also discussed     

紫外电晕检测仪在电晕放电检测中的应用

首先阐述一种新型紫外电晕检测仪的原理,介绍该仪器目前在国外的应用情况,然后分析该类仪器在系统应用中技术特点和存在的一些问题,最后结合电力系统快速发展的展望了应用的前景。     

Multiple-needle corona electrodes for electrostatic processesapplication

Corona from high-voltage electrodes is employed in various electrostatic installations, such as ozonizers, air filters, powder sprayers and separators. Multiple-needle electrode designs are preferred whenever low corona onset voltage and good resistance to mechanical shocks are required. This paper aims at identifying a simple solution to overcome the main drawback of this type of electrode, the nonuniformity of the generated space charge. Experiments were carried out with various models of electrodes, having one or several rows of stainless steel needles. A current probe, consisting of an enameled copper wire (0.4 mm diameter), was embedded in the center of a plane collecting electrode. For a given interelectrode distance (5-50 mm) and a fixed position of the multiple-needle electrode, the collecting plate was translated along two orthogonal directions, so that the current probe could scan a 75 mm×75 mm square. The results depended on the interelectrode distance and on the high-voltage level. An explanation is given to some observations made on a roll-type electrostatic separator provided with two models of multiple-needle corona electrodes. An improved electrode design was proposed for the industrial installations     

A measurement method for atmospheric ion mobilities based on cylindrical electrodes in direct current corona discharge

Ion mobility is one of fundamental parameters to describe the motion of ions in an electric field and a significant quantity to calculate the ionized field and ion current density of ultrahigh‐voltage direct current (UHVDC) power lines. This paper presents a measurement method for atmospheric ion mobilities in a DC corona discharge. An apparatus with coaxial cylindrical electrodes is designed and utilized. A vibrating electric field meter is employed to measure the ionized field of the electrode. Experimental results show that under atmospheric conditions, the average positive and negative ion mobilities are 1.76 × 10⁻⁴ and 1.88 × 10⁻⁴m²·V⁻¹·s⁻¹, respectively. The proposed method is compared with previous works of others. The impact of fluctuations of the measured ionized field and ion current density on the results of ion mobilities is also analyzed. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Negative DC corona discharge effects on the ultraviolet photon count in rod to plane air gaps

In order to investigate the effects of negative DC corona discharge on ultraviolet (UV) photon count, a corona discharge measurement system based on rod to plane air gaps was established. The variations of positive ion, negative ion, and electron densities were calculated with a fluid model, and the generation process of photons during negative corona discharge was investigated. The differences of photon count and the variation of charged particles between negative and positive corona were also compared. The corona current, Trichel pulses, and corona‐generated photons were measured with increasing applied voltage. An approximate parabolic relationship found to exist between the photon count and the corona current, and also an ideal quadratic function was found to exist between the photon count and the frequency of Trichel pulses. These results provide a solid foundation in the application of UV imaging detection of negative DC corona discharge in power equipment. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Agglomeration of particles by ac corona discharge

Improving the collection efficiency for particles smaller than 1 μm on every precipitator is important. We sought to improve the collection of these particles on an ESP due to particle agglomeration. Particles are charged by ac corona discharge in a precharger and agglomerated by a dc electric field in an agglomerator downstream of the precharger. Diesel exhaust particles were used as particulate matter for the experiments. The distribution of particle size was measured using a particle counter and a scanning electron microscope. By these methods, particles as small as 0.01 μm could be counted. Results showed the agglomeration between particles at ac corona discharge operating mode. The concentration of particles smaller than approximately 0.35 μm decreases, and that of particles larger than approximately 0.35 μm increases in the agglomerator. The agglomeration rate increases with increasing applied voltage, then saturates. These results may be due to the size distribution and to decrease of concentration by agglomeration. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 30–37, 2000     

Control and performance of a pulse-density-modulatedseries-resonant inverter for corona discharge processes

This paper presents the control and performance of a pulse-density-modulated (PDM) series-resonant voltage-source inverter developed for corona discharge processes. The PDM inverter produces either a square-wave AC-voltage state or a zero-voltage state at its AC terminals to control the average output voltage under constant DC voltage and operating frequency. This results in a wide range of power control from 0.5% to 100%, even in the corona discharge load with a strong nonlinear characteristic. A 30 kHz 6 kW surface treatment system consisting of a voltage-source PDM inverter, a step-up transformer, and a corona discharge treater shows the establishment of a stable corona discharge in an extremely wide range of power control and, therefore, succeeds in performing both strong and weak surface treatment processes for film     

Pulsed corona discharge for hydrogen sulfide decomposition

The results of the use of a wire-in-tube corona reactor, energized by short voltage spikes, to decompose small concentrations of hydrogen sulfide contained in hydrogen are presented. Parameters investigated include the reactor geometry, hydrogen sulfide concentration, corona power, and the nature of the product. Electronic-molecular interactions are considered, and a mathematical model is formulated that accurately predicts experimental results     

Simulation of corona discharge. Negative corona in SF6

Negative coronas in SF₆ under three voltage levels are investigated by Monte Carlo simulation. For the purpose of simulation, the gap between a hyperboloidal needle and a plane is divided into two regions: region I where the electric field is very steep and most electrons and ions are accumulated, and region II the rest of the gap. In region I electron motion is simulated by dividing the region into a number of cells and a small cell size improves the accuracy. The magnitude of current pulse increases with increasing voltage and there appears to be more than one peak in each pulse as observed by experiment. The development of electron avalanches is due to ionization and photoionization in the high field region, while the quenching of the avalanches is due to the space charge field suppression. Also the accumulation of positive and negative ions are displayed in detail. The space charge field distortion is studied and found to increase with increasing applied voltage     

Simulation of corona discharge. Positive corona in SF6

Positive coronas in SF₆ under three voltage levels, 3.0, 3.5 and 4.0 kV, are studied for a 0.5 cm gap between a hyperboloid needle and a plane electrode at a gas number density N=2.12×10¹⁸ cm³. The current in the form of a burst of pulses is found to increase with increasing voltage. The initiation and development of successive avalanches are traced as function of time after voltage increases. The development of electron avalanches and streamers are due to ionization and photoionization and quenching of avalanches is due to space charge. The simulation provides a detailed structure of avalanches from which essential differences between positive and negative corona with regard to total field distribution, propagation of successive avalanches and ion distribution can be discerned     

Nonlinear boundary-value problem for cylindrical corona discharge

Contents Closed-form (one-dimensional) solutions are derived for the electric fieldE(r) and potentialV(r) in a positive ion discharge between a stressed wire anode atr=a and a coaxial cylinder cathode atr=b. It is shown that this system sustains two different corona discharge modes, namely with radially (i) decreasing (k<1) and (ii) increasing (k>1) electric field strengthE(r), wherek=E _I /E _a is the crucial discharge number. E_I = (I/2₀)^1/2 [V/m] is given in terms of the discharge currentI [A/m], whereas the electric fieldE _a [V/m] at the anode depends on currentI and ion temperatureT _i at the cathode. The physical properties of these discharge modes are discussed analytically.

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Nichtlineares Randwertproblem der zylindrischen Korona-Entladung

Übersicht Geschlossene (eindimensionale) Lösungen werden abgeleitet für das elektrische FeldE(r) und PotentialV(r) in einer positiven Ionen-Entladung zwischen einer Hochspannungsanode mit Radiusr=a und einer koaxialen Zylinderkathode mit Radiusr=b. Es wird gezeigt, daß in diesem System zwei verschiedene Typen von Korona-Entladungen existieren können, nämlich mit radial (i) abnehmender (k<1) und (ii) zunehmender (k>1) elektrischer Feldstärke, wobeik=E _I /E _a der kritische Entladungsparameter ist. E_I = (I/2₀)^1/2 [V/m] ist durch den EntladungsstromI [A/m], während das elektrische FeldE _a [V/m] an der Anode durch StromI und IonentemperaturT _i an der Kathode bestimmt ist. Die physikalischen Eigenschaften dieser Entladungstypen werden analytisch diskutiert.

     

高压外部电晕放电及其检测

从电晕放电现象出发,简单介绍了电晕放电的形成机制,分析了高压输变电系统中高压外部电晕放电的基本特征及危害;介绍了传统电晕放电检测方法(红外成像和超声波测量)及其不足,详细阐述了紫外成像检测新技术的原理、技术特点、应用领域,展望了紫外成像检测技术在高压输变电系统中的应用前景。     

The electric corona discharge in the triode system

In this paper, the charge density, electric field and corona current distributions in the corona triode are calculated using a hybrid technique; the finite-element method and the boundary-element method are combined with the method of characteristics. The characteristic lines are traced backward from points of the analyzed domain to the corona wire. The current density, electric field and space-charge density distributions can be controlled by changing the configuration of the system. The voltage applied to the grid plays an important role in controlling the corona current. Results of calculations in a number of different cases show the influence of different parameters on the characteristics of the corona triode     

空气局部放电衍生物气体生成规律的研究

分解气体分析法通过检测故障产生的气体组分诊断设备故障,是检测电力设备故障的重要方法,在一些应用场合具有不可替代的作用。然而目前该方法只在绝缘油、SF6等绝缘介质的场合有应用,对于空气这一最重要的绝缘介质少有应用。本文搭建空气局部放电过程模拟实验平台及气体产物检测系统,研究放电衍生物气体生成规律。分别采用两种检测方式对气体产物进行检测,结果显示O_3、NO、NO_2为空气放电的主要产物;在放电强度较低时,空气放电主要分解产物为O_3,放电强度进一步增大可以检测到氮氧化物NO和NO_2的产生,且臭氧O_3浓度远大于氮氧化物气体浓度;对于封闭空间,随着放电时间增长分解产物浓度增加,但趋向饱和,且随着施加电压增大,气体产物浓度增加;而在相同放电电压下,空气相对湿度变化对气体产物含量有明显影响,O_3、NO_2的浓度在相对湿度为18%时高于相对湿度为25%和44%时的值;而NO的浓度在相对湿度为44%时高于相对湿度为18%和25%时的值,同时差异较小。     

Monte Carlo simulation of electrical corona discharge in air

Electrical discharges play a key role in technologies; there are many industrial applications where the corona discharge is used. Air as insulator is probably the best compromise solution for many applications. All of this reflects on the great importance of the evaluation of the corona performance characteristics. Numerical simulation of the corona discharge helps to better understand the involved phenomena and optimize the corona devices. This paper is aimed at calculating the corona discharge in negative point-plane air gaps. To describe the non-equilibrium behavior of the electronic avalanches and to simulate the development of corona discharge the method of Monte Carlo has been used. This model provides the spatial-temporal local field and particles charged densities variations as well as the ionization front velocity.