Characteristics Of Corona Discharge Research Articles

The current pulses characteristics of the negative corona discharge in SF6/CF4 mixtures

This paper presents the results of numerical investigation of the current pulses characteristics in SF6/CF4 mixtures for the negative point-plane corona discharge. The pressure and the temperature of gas mixtures are 0.4 MPa and 300 K, respectively. The CF4 content varies from 20% to 80%. The 2D axisymmetric geometry with point-plane electrodes is investigated, and the three drift-diffusion equations are solved to predict the characteristics of the negative corona discharge. In addition, Poisson’s equation is coupled with the above three continuity equations to calculate the electric field. In order to calculate the electron impact coefficients, including the Townsend ionization and attachment coefficients, as well as the mobilities and diffusion coefficients for electrons, the two-term Boltzmann equation is solved. The characteristics of three ionic species at five stages of the first current pulse in 60%SF6-40%CF4 and 20%SF6-80%CF4 mixtures are selected to discuss the development mechanism of current pulses. Moreover, the reduced electric field strengths at the corresponding time instants are presented to help understand the discharge process. The current waveform and the total number of three species are compared in all the cases to analyze the effects of the CF4 content on the discharge. The reduced electric field strength is also helpful in understanding the effects of CF4 content. When the CF4 content increases to 80%, the discharge is more intensive and the pulse frequency also increases.

Effect of Temperature on Current Pulse Characteristics of Negative Corona Discharge Based on Numerical Model

Temperature is an important factor affecting the dynamic processes of corona discharge, since the ionization, attachment, and mobility of charged particles are directly related to temperature. Most existing research has investigated the temperature effect on corona discharge through experimental works. However, they are hard to acquire the corona discharge microphysical processes, which are related to the formation of the current pulse and electromagnetic (EM) wave signals. This article proposes a numerical model with temperature-related transport parameters to study the temperature influence on microphysical processes and current pulses for negative corona. By comparing microphysical quantities such as the effective ionization coefficient, density, and velocity of space charges, the effect of temperature on the current pulse parameters including the rise and fall times, amplitude, and pulsewidth is systematically explained. It shows that as the temperature rises, the current pulse amplitude increases, while the other three parameters decrease. The rise time is dependent on the effective ionization coefficient. The fall time is affected by the velocities of negative and positive ions. The experimental results indicate the simulated current pulses are consistent with the measured ones, proving the effectiveness of the proposed numerical model with temperature variation.

New Signal Processing-Based Methodology for Optimal Feature Selection of Corona Discharges Measurement in HVDC Systems

This article presents a new method based on the combination of digital signal processing parameters for the selection of optimal characteristics of corona discharges in HVDC systems, particularly for linearization of the discharge model for applications that require a simplified computational approach. The proposed method implements a new metric from the coefficient of variation, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CV_STFT</i> , based on the short-time Fourier transform (STFT) and the Hinkley criterion to measure the spectral variability and determine the corona discharge profile in different situations. An experimental analysis was performed by applying voltages between ± 30kV and ± 100 kV in a conductor, and electrical current signals proportional to the corona effect were collected through a data acquisition system. The results indicated that the application of the new method was successful in quantifying, in a simple way, the percentage of growth of corona discharges as a function of the voltage applied within the range of 40-80 kHz. Moreover, it showed 90 %, 91 %, 92%, 97%, 89%, 92%, and 93% of reliability in calculating the root-mean-square deviation (RMSD) based on approximation by a linear model. The frequency band resulting from this study proved to be favorable to establishing a threshold for the percentage of corona discharge growth according to its profile or condition of application, indicating this information may be useful in the construction of mobile devices with low consumption and computational performance, meeting the demands of Industry 4.0 and the Internet of Things.

Negative corona discharge and flow characteristics of a two-stage needle-to-ring configuration ionic wind pump for temperature and relative humidity

Ionic wind pumps have the advantages of a compact structure, no moving parts, and low power consumption. The effects of temperature and humidity on the current–voltage and flow characteristics of ionic wind pumps are still unclear. This study experimentally investigates the effects of temperature and humidity on the breakdown voltage, discharge current, and velocity of a two-stage needle-to-ring type ionic wind pump with a negative corona discharge. It is found that the coupling effects of temperature, humidity, and water vapor condensation determine the current–voltage and flow characteristics of ionic wind pumps. The temperature and vapor condensation effects can enhance the discharge current and outlet velocity and weaken the breakdown voltage. However, the humidity effect can weaken the discharge current and outlet velocity, and improve the breakdown voltage. Moreover, there exists a competition between humidity and vapor condensation effects on breakdown voltage, current, and velocity. The increase in temperature intensifies the humidity effect and weakens the condensation effect; thus, the temperature changes the contribution of humidity and condensation effects in the competition. A working spectrum of ionic wind is provided in the temperature and humidity coupling environment, including a vapor condensation-controlled zone, a sensitive humidity zone for breakdown voltage and velocity, and an insensitive humidity zone for breakdown voltage and velocity. The spectrum can provide theoretical guidance for designing ionic wind pumps at different temperatures and humidity.

Influence of AC corona discharge on the hydrophobicity of silicone rubber surface in high-speed airflow environment

Corona discharge is one of the key factors that lead to the hydrophobicity loss of silicone rubber insulators used on the roof of high-speed trains. Based on the artificial experimental wind-tunnel platform, influences of AC corona intensity and airflow velocity on the hydrophobicity distribution of the silicone rubber surface were studied. According to the corona discharge phenomena and measured discharge current, influences of airflow velocity and voltage on the characteristics of corona discharge in a high-speed airflow environment were discussed. Results reveal that the hydrophobicity distribution on the silicone rubber surface shifts along the airflow direction in the high-speed airflow environment when the voltage is relatively high. When ionization zone develops to the needle-plate gap, the discharge path is deflected to the direction of airflow, which is responsible for the change of the hydrophobicity distribution. It is notable that the deflection distance decreases with the increase of airflow velocity. This is attributed to the fact that the electrons with variable horizontal distance from the electron to the plate electrode center are subjected to different electric field forces, resulting in different influences of high-speed airflow on them. These results are of engineering and theoretical significance for insulators used in high-speed railways.

A novel method to predict current–voltage characteristics of positive corona discharges based on a perturbation technique. II. Global analysis and applications to electrohydrodynamic thrusters

Electrohydrodynamic (EHD) thrusters can silently propel small unmanned aerial vehicles without moving parts using corona discharges. Computational fluid dynamics would be a powerful tool to model the EHD thrusters and then optimize them. The drift-diffusion-Poisson equations govern corona discharges; hence, the equations can predict the current–voltage characteristics curves of EHD thrusters. However, the equations are too stiff to analyze EHD thrusters in the time domain. Here, we propose a perturbation technique to efficiently solve the stiff drift-diffusion-Poisson system in global (i.e., full two-dimensional or three-dimensional) and nonlinear (i.e., applied voltages higher than the corona inception voltage) regimes. Furthermore, we validated the method with the experimental results of a previous study.

Influence of Protrusion Tip Size on Current Pulse Characteristics of Negative Corona Discharge Based on Numerical Simulation

The tip size of metal protrusions is an important factor affecting corona discharge, since it influences the electric filed, the ionization range and strength around the protrusion defect. Most existing studies on the influence of protrusion tip size on corona discharge are implemented by experimental methods. However, these studies are difficult to obtain the microphysical process of charged particles, which is related to the generation of current pulses and electromagnetic (EM) waves. In this paper, a hydrodynamic simulation model is proposed to study the effect of protrusion tip size on the microphysical process and current pulses of negative corona discharge. A mapping relationship between microscopic behaviors of charged particles and current pulses is established by this simulation method. Based on the comparison of microphysical quantities, the effect of defect tip size on the detailed parameters of current pulses is clearly explained. It shows that with the increase of tip size under a constant voltage, all the five parameters of current pluses increase. The rising time is related to the effective ionization coefficient, while the falling time is dependent on the velocities of positive and negative ions. The experiment and simulation results coincide in current waveforms and all five parameters.

Numerical Investigation of Negative Corona Discharge From Protrusion on Parallel Plane Electrodes in Air Insulation

Compared to a spherical metal particle motion within gas insulation, a wire-type particle could have a standing position on the ground electrode. In this work, a numerical investigation and validation from the experimental data of corona discharge from a small protrusion in air insulation within a uniform field under a dc voltage are performed. Three drift-diffusion models and Poisson equations are employed and solved using a finite element method to investigate negative corona discharge phenomena. The results show that the current characteristic with different applied voltages is within good agreement with the experimental results. A typical pulse train and the total number of charged species are also presented. Furthermore, the spatial distribution of charged species, the electric field distribution, and the ionization rate are explained. The effect of physical geometries of the particle on negative corona discharge characteristics is also investigated. It is found that the variation of the particle length, diameter, and tip radius is influencing the pulse characteristics.

Research on the Simulation Method for HVDC Continuous Positive Corona Discharge

Corona current is one of the most direct parameters to describe corona discharge. Accurate simulation for corona current is very important for studying the physical process and characteristics of corona discharge. It can provide the theoretical basis for solving electromagnetic environment problems and optimizing transmission lines. A simulation method for high voltage direct current (HVDC) continuous positive corona discharge is presented in this article. First, based on the experiments of continuous positive corona discharge under the different voltages, the regularity of time intervals between adjacent current pulses is obtained. Then, a two-dimensional simulation model of the positive continuous corona discharge process is established with the obtained regularity, which is used to imitate the electron re- emission in the simulation. Finally, the correctness and validity of the method are verified by the experimental results. Since the proposed model is more in line with the actual situation than the existing equal-time interval model, the change and motion process of various ions in the discharge process will also be more realistic. The results are helpful to further understand the corona discharge process and provide a theoretical reference for the design of HVDC transmission lines.

Characteristics and Underlying Physics of Bipolar Corona Discharge of Floating Conductor

Bipolar corona discharge is the fundamental phenomenon that preoccurs in air breakdown for nongrounded objects facing a high-voltage source, which sets important bases for aircraft protection crossing thunderclouds and improvement of high-voltage switches with floating conductors, while this phenomenon has not been fully understood to date. This article proposes a bipolar corona plasma model (BCPM) based on the plasma hydrodynamic process and the chemical reactions of air discharge. The numerical analysis of the charged particle distribution matches the experimental result of the bipolar corona discharge appearance. Furthermore, the characteristics of bipolar corona discharge are described from the perspective of electric field and electron current density at the two opposite ends of the floating conductor. Results show that, at the positive end, the corona discharge has a long columnar shape in a faint light blue. While at the negative end, the corona presents a spherical shape in a stronger luminous light purple. There exists a density extremum at the position 0.03 cm away from the conductor ends in the distribution of electrons, where a low electron density zone with a concentration of 0.42 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{13}\,\,\text{m}^{-3}$ </tex-math></inline-formula> forms at the positive end, while electrons group to a high density of 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{16}\,\,\text{m}^{-3}$ </tex-math></inline-formula> at the negative end. The geometric length of the high-density ions zone is enlarged by 2 times at the positive end compared to the negative end. The peak electric field at the negative end is about 1.5 times stronger than the electric field at the positive end, consistent with the space charge distribution at the positive and negative ends. The unbalance of the emission and entry of electron current results in a slightly positive polarity for the floating conductor. This study can be consulted for shedding light on the underlying physics of bipolar corona discharge of floating conductors.

Research on Wire-to-Two Fin Configuration for Positive Atmospheric Plasma by Electrokinetic Blower

Interest in the development of electro-fluid-dynamic devices (EFDs) based on corona discharge is growing due to their advantages and applicability across different industrial sectors. On the one hand, their performance as forced convection motors, in terms of weight, volume, and absence of noise and moving parts, make them competitive against traditional systems such as fans. On the other hand, the actions of the corona discharge, in terms of elimination of viruses and bacteria, are already known. This paper studies the characteristics of corona discharge in terms of air flow for a new proposed configuration and geometry of electrodes. A systematic study is performed through a parametric study of the distances, power consumption, and size of the corona electrode. The characteristic voltage–current (CVCCs) and flow–pressure curves obtained provide design rules to use the generated corona discharge and the device itself, as a silent air propeller, which may also sterilize the surrounding environment and surfaces.

3D Corona Discharge Model and Its Use in the Presence of Wind During a Thunderstorm

In this study, the authors developed a three-dimensional (3D) numerical model for the diffusion of positive corona charges based on a 2D model with a uniform grid to explore the characteristics of corona discharge at a building tip during a thunderstorm in the presence of wind. The variable-grid meshing method is used to solve the problems of implementing a large simulation domain for thunder clouds (kilometer-scale) and the minute calculations of corona discharge at the tip (centimeter scale) in the 3D numerical simulation. The proposed model has advantages in terms of the acquisition of the parameters of corona charges and the spatial distribution of the electric field (E-field) in the environment. We used positive corona discharge at the tip of a building under a negative thunderstorm, along with three wind fields (horizontal wind, updraft, and downdraft with wind speeds of 10 m/s) as an example. The presence of the wind increased the density of corona charges at the tip, where the horizontal wind was the most beneficial for its occurrence. Moreover, the characteristics of distortion of the electric field around the tip were significantly different, owing to the different directions of the wind. Downdraft led to the maximum enhancement in the E-field above the tip, and updraft prompted the minimum increase in it, by only 1.19 times. However, the opposite results were obtained for the enhancement in the spatial range of the charges: The updraft led to the greatest increase in it, and the downdraft caused the smallest. Corona charges had an apparent shielding effect on the E-field below the tip and can even change the polarity of the E-field in a small area close to it. The strongest shielding effect on the ground E-field occurred in the case of the downdraft, which decreased the E-field to 0.36 times compared with that without the corona charges. On the contrary, corona discharge had the weakest shielding ability on the ground when it met the updraft. The horizontal wind had the largest range of shielding on the ground, of up to 14,699.36 m2, while the updraft had the lowest, at only 6,170.91 m2.

The durability of superhydrophobic and slippery liquid infused porous surface coatings under corona discharge characteristic of the operation of high voltage power transmission lines

Application of polyfunctional water-repelling coatings for high voltage outdoor power lines wires, insulators, and line supports recently gathered large interest due to their ability to substantially boost performance. Such functionalization can mitigate the accumulation of water precipitates and atmospheric pollutions, decrease leakage current, increase flashover and corona ignition voltage. However, harsh conditions concomitant to a high voltage such as high energy ions and electrons, high ozone concentration, UV radiation impose strict requirements on the durability of applied coatings. In this paper, we focus on the analysis of the durability of superhydrophobic coatings (SHC) and slippery liquid infused porous surfaces (SLIPS) under prolonged exposure to industrial grade alternating current corona discharge. Reported results show that in contrast to previously reported low resilience of polymer-based SHC, proper metal-based SHC withstands many hours of exposure without notable degradation. The obtained data on the stability of SLIPS under corona discharge show notable degradation related to the high rate of infused layer depletion. Overall, reported results broaden the understanding of the effect of corona exposure on functional materials and reinforce the optimistic view on the applicability of SHC and SLIPS coatings in the power transmission industry.

Discharge characteristics in soil under positive pulse voltage superimposed DC component

Considerable research efforts have been devoted to the study of the application of atmospheric discharge in soil remediation. Most of them focused on how to improve the degradation efficiency of specific pollutants. In contrast, the generation and development of discharge in soil is less studied, which restricts the widespread application of soil remediation. Pulse voltage is widely used to trigger discharge in soil, but the requirement for the power supply is relatively high. The current paper proposes a new form of discharge voltage, with positive pulse voltage superimposed on DC bias. The results show that the existence of DC component can effectively lower the required pulse voltage and enlarge the active corona volume, in which area most ionization and excitation happens. The characteristics of corona discharge in soil under DC voltage only, pulse voltage only and superimposed voltage with various voltage components are discussed in detail, according to the volt-ampere characteristics and discharge images from a series of experiments. The mechanism behind the experimental phenomenon are also discussed.

Corona Discharge Characteristics in Electrostatic Precipitator Under High Temperature

Harmful substances, such as particulate matter (PM), nitrogen oxides, and sulfur compounds in exhaust gas emitted from marine diesel engines have a great impact on the air environment. Among them, especially black carbon in PM has a negative effect on global warming. The exhaust gas from marine diesel engines using fuels containing heavy fuel oil has a high PM concentration and high temperature. Therefore, a commonly used diesel particulate filter is not suitable for collection because it tends to cause clogging and reduce efficiency. Furthermore, it is often the case that ships are at sea for more than one month, so it is difficult to replace the filter, that is, maintenance is difficult. On the other hand, an electrostatic precipitator (ESP) has the advantages of a simpler structure, lower pressure loss, and higher collection efficiency of high concentration particles. This suggests that the ESP is suitable for collecting harmful substances from the marine diesel exhaust gas. At high temperatures, corona discharge is unstable, and a flashover tends to occur at low applied voltage. Therefore, it is necessary to study the stable corona discharge generation range for the stable operation of the ESP. The purpose of this research is to analyze the optimal electrode structure and its corona discharge characteristics under the simulated exhaust gas of a diesel engine in the range of 100 °C – 400 °C using a negative dc power supply.

Research on Simulation Method of UHVDC Corona Discharge

Ultra high voltage direct current (UHVDC) transmission has took a significant part in power grid. However, the increase of transmission efficiency hindered by electromagnetic environment problems caused by its corona discharge. Therefore, the corona discharge of UHVDC transmission line has been spotlighted. Considering the complex reaction of microscopic particles in the air during the discharge process, this paper integrates each split conductor as a discharge source located on the split centerline, and simplifies the discharge of the transmission line into a one-dimensional model of a coaxial cable. The study can help us to explore the physical process and microscopic particle motion characteristics of corona discharge deeply. Besides, it is an important guideline for studying and preventing electromagnetic environment problems from the root cause.

Study on Corona Aging Characteristics of Silicone Rubber Material under Different Environmental Conditions

In this article, a silicone rubber-based composite material is selected as the test sample, and a 100-h corona aging test is conducted under different environments using multiple pin-plate electrodes to study the corona discharge characteristics of pin-plate under different humidity, salt fog, and haze environments. The corona aging characteristics of silicone rubber material are analyzed by the static contact angle, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). The results show that, with the increase in the relative humidity (RH), the frequency and energy of corona discharge increase. The discharge frequency under a haze environment is small, but the number and amplitude of the positive half-cycle pulse are larger. With the increase in RH and the deterioration of the environment, the oxidation degree and hydrophobicity loss rate of the material surface are accelerated, and the material surface damage is also aggravated. The aging characteristics of silicone rubber have a positive correlation with the content of water molecules in the air, some hydrophilic -OH, and acidic -COOH appear on the material surface, leading to the insulation performance decrease. As the aging of silicone rubber deepens, its equivalent transverse relaxation time drop increases, the number of H atoms that become low bond energy state inside increases, and the resistance to corona aging decreases. The results of this article can provide some reference for the evaluation, diagnosis, and production of composite insulators in different regions.

Numerical Study on the Effect of Electric Field Non-uniformity on the Pulse Characteristics of Positive Corona Discharge in SF6/N2 Gas Mixtures

This paper establishes a two-dimensional axisymmetric needle-to-plane geometry model in SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> /N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas mixtures to simulate the effect of the electric field non-uniformity on the pulse characteristics of positive corona discharge. By changing the needle tip radii from 25 µm to 300 µm, the corona discharge process under different electric field non-uniformity is simulated. Meanwhile, the simulated results are verified by the experiments on a corona discharge experimental setup. The results show that the rising and falling edges of positive corona current pulses correspond to the development and termination of streamers, respectively. The sub-pulse will be generated during the formation of the first current pulse, and this phenomenon is closely related to the applied voltage. The generation of sub-pulse is expected to be a feature of positive corona discharge in SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> /N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas mixtures entering the brush-pulse stage. With increasing the electric field non-uniformity, the onset voltages of two characteristic pulse stages, including the streamer-pulse stage and brush-pulse stage, decrease. Moreover, the first current pulse amplitude increases, and the pulse-repetition rate presents an approximate exponential increasing trend.

Corona Discharge Characteristics under Variable Frequency and Pressure Environments.

More electric aircrafts (MEAs) are paving the path to all electric aircrafts (AEAs), which make a much more intensive use of electrical power than conventional aircrafts. Due to the strict weight requirements, both MEA and AEA systems require to increase the distribution voltage in order to limit the required electrical current. Under this paradigm new issues arise, in part due to the voltage rise and in part because of the harsh environments found in aircrafts systems, especially those related to low pressure and high-electric frequency operation. Increased voltage levels, high-operating frequencies, low-pressure environments and reduced distances between wires pose insulation systems at risk, so partial discharges (PDs) and electrical breakdown are more likely to occur. This paper performs an experimental analysis of the effect of low-pressure environments and high-operating frequencies on the visual corona voltage, since corona discharges occurrence is directly related to arc tracking and insulation degradation in wiring systems. To this end, a rod-to-plane electrode configuration is tested in the 20–100 kPa and 50–1000 Hz ranges, these ranges cover most aircraft applications, so that the corona extinction voltage is experimentally determined by using a low-cost high-resolution CMOS imaging sensor which is sensitive to the visible and near ultraviolet (UV) spectra. The imaging sensor locates the discharge points and the intensity of the discharge, offering simplicity and low-cost measurements with high sensitivity. Moreover, to assess the performance of such sensor, the discharges are also acquired by analyzing the leakage current using an inexpensive resistor and a fast oscilloscope. The experimental data presented in this paper can be useful in designing insulation systems for MEA and AEA applications.

Lightning Surge Analysis for Overhead Lines Considering Corona Effect

Corona discharge characteristics are measured in a corona cage. The difference is found between the q–u curves under double exponential and damped oscillation surges. The behavior of the minor loops is revealed for the q–u curves under positive and negative damped oscillation surges. An extended improvement is made on the traditional approach for modeling of the q–u curves under damped oscillation surges. The extended approach has the capability of describing the complicated trajectory feature of the minor loops. On the basis of the extended approach, an efficient method is proposed for performing lightning surge analysis of overhead lines considering the corona effect. In the proposed method, an overhead line with corona is divided into a certain number of line segments. Each segment is converted into a circuit unit consisting of a non-linear branch and a linear circuit. With these circuit units connected in sequence, a complete equivalent circuit is constructed for the overhead line with corona. The transient responses can be obtained from the solution to the equivalent circuit. Then, the calculated results are compared with the field test results on a test overhead line.