Positive Glow Corona Research Articles

Effects of trace oxygen on the self-oscillation of positive glow corona in nitrogen near atmospheric pressure

Effects of trace oxygen on the self-oscillation of positive glow corona in nitrogen near atmospheric pressure

Revisiting the theory of positive glow corona with a comprehensive kinetic scheme

The theory of positive glow corona is revisited by performing a detailed simulation based on the fluid model with a comprehensive kinetic scheme (CKS). The kinetic scheme includes 28 species, 127 chemical reactions for N2/O2 mixture. The simulation results are compared with that from an averaged kinetic scheme (AKS) which considers only five species and seven reactions. The two models give similar predictions in terms of discharge current. However, several differences in details of the results bring new physical insights to the theory of positive glow corona. It is shown that, the model with the AKS underestimates the detachment effect that plays an important role in positive glow corona discharge. Moreover, the wave-front of the current pulse calculated by the model with the CKS has a smaller steepness, a lower peak-to-peak value, and a longer rise time. These results are in better agreement with the experimental measurement reported in the literature. It is also found that the positive space charge of glow corona is dominated by O2 + in the ionization layer and by O4 + in the drift region far away from the anode. Negative ions are produced in the ionization layer close to the anode and the main species are O− and O3 −.

Electric field dependence of SF6 nonlinear discharge characteristics: N-curve estimations

The N-curve of SF6 describes the relationship between the AC breakdown voltage in an extremely inhomogeneous electric field and pressurized SF6 gas. It is directly dependent on the electric field distribution, which is determined by the gas gap, curvature radius, and background electric field. An increase in gap distance, a decrease in curvature radius, and relatively weak background electric field are all conducive to corona stabilization. The electrode curvature radius is the determining factor in the positive glow corona (PGC) discharge quenching pressure. The breakdown voltage dominated by the streamer mechanism can be estimated accurately by calculating the electric field based on the Deutsch assumption and combining it with the SF6 static field breakdown criterion. The proposed method is applicable to the estimation of N-curves in gaps with varying field distributions. The work presented in this paper may support further quantitative research on the discharge mechanism of strongly electronegative gas dielectrics.

Neglected culprit of nonlinear discharge characteristics in SF6: shielding effect induced by positive glow corona discharge

The discharge characteristics of SF6 dependent on gas pressure under extremely inhomogeneous electric fields are strongly nonlinear and must be carefully considered when optimizing gas-insulated equipment insulation design and defect detection. The main aim of this study was to determine the relationship between nonlinear breakdown characteristics and the pre-breakdown discharge mode transition. The breakdown model established by Niemeyer, as adapted under impulse voltage, was expanded. The images and the phase-resolved patterns of the pre-breakdown discharge as a function of gas pressure and applied voltage were analyzed to observe the relationship between them as per the spatial distribution of the spark paths. A universal model of the nonlinear breakdown phenomenon under steady-state voltage was established accordingly. Experimental results demonstrate the existence of a positive glow corona (PGC) discharge in the interval with the discontinuous breakdown voltage as well as significant interactions between the PGC discharge and leader discharge. The nonlinear characteristics can be attributed to the inception and quenching of the PGC discharge. The shielding effect induced by the PGC discharge is the neglected culprit of the strong nonlinear discharge characteristics under steady-state voltage. The nonmonotonic U–p curve in electronegative gases was also assessed in an effort to build a theoretical basis for the manufacture and condition monitoring of the gas-insulated equipment.

Simulation on the development progress of positive glow corona discharge from ground wire of AC/DC transmission lines under thunderstorm condition

In thunderstorm weather, lightning induction appears on the surface of ground objects, and then the positive glow corona is initiated, which influences the selection of lighting targets by lighting leader. So, it has great research value for lightning protection of AC/DC transmission lines. Here, a two-dimensional model of positive glow corona is established in COMSOL Multiphysics. From the simulation results of its development progress, corona current, ion distribution, and migration are revealed. The positive ions are in a round symmetric distribution at the initial stage of migration, but when the ions move farther away, ions become an elongated oval distribution. Also, most of the ions move to the thundercloud in the end. The positive ions accumulate above the transmission line and form a positive background, which has confinement and attenuation to electronic beam. Therefore, the probability of the electron avalanche converted into flowing is reduced. Meanwhile, the positive background promotes the compound of ions and electrons. As a result, the initiation of upward leader is suppressed and so the selection of lighting targets by lighting leader is influenced.

On the transition from stable positive glow corona to streamers

A 2D numerical simulation of the transition from stable positive glow corona to streamers in coaxial cylindrical configuration is presented. The hydrodynamic model with several convection-dominated continuity equations together with Poisson equation are solved with consideration of the ionization layer. The transition from a stable positive glow corona produced under a DC voltage to streamers is investigated under a sudden change of the applied voltage. The critical rate of rise of voltage required for the transition from positive glow to streamer corona is evaluated with a voltage ramp. By introducing either physical or numerical instabilities into the model, streamers with filamentary structures are observed, which produce a sudden increase of the discharge current by more than two orders of magnitude. It is also found that the surface electric field of the corona-generating conductor deviates from the onset electric field, casting doubts about the validity of Kaptzov’s approximation to evaluate the transition from stable glow to streamers.

Numerical simulation of positive glow corona discharge initiated from long ground wire under thundercloud field

With the slow effect of electric field of thundercloud, a kind of positive glow corona without streamers is initiated from the surface of object near the ground, and a large number of positive space charges are injected into the surrounding space, consequently, lighting targets selected by the lighting leader can be changed. In this paper, a numerical simulation of positive glow corona discharge initiated from the long ground wire with the effect of the electric field of thundercloud is presented. In consideration of the attachment and collision effects between positive ions and other ions, an accurate two-dimensional positive glow corona model is established. Meanwhile, a high-voltage corona discharge experiment is done in the laboratory to measure the corona current in different background electric fields, and the results are compared with the simulation results in order to verify the correctness of the model established in this paper. According to the established model, the initiation and development progress of glow corona with the effect of thundercloud are simulated and the corona current, laws of positive ion density distribution and migration are revealed. Results show that positive ions generated from the glow corona discharge present a circular symmetric distribution in the plane perpendicular to the ground wire at their early stage of migration, but the distribution is shaped as an elongated oval later when the ions move farther from the ground wire for the effect of electric field of thundercloud, that is to say, the overwhelming majority of the ions will be finally distributed in the upper area of the ground wire and gradually migrate towards the thundercloud. Due to the accumulation effects of positive ions in the upper migration area near the ground wire, the positive space charge background is formed, which has a damping effect on the electron beam. Thus the formation of electron avalanche is suppressed and the probability for electron avalanche to be converted into streamer is reduced. Meanwhile, the positive space charge background improves the collision surface of the gas and increases the compound probability between positive ions and electrons. Therefore, the conversion processes from electron avalanche and streamer to upward leader are impeded and the initiation of upward leader is suppressed.

Qualitative gas temperature distribution in positive DC glow corona using spectral image processing in atmospheric air

An experimental method of determining a qualitative two-dimensional image of the gas temperature in stationary atmospheric nonthermal plasma by spectral image processing was presented. In the experiment, a steady-state glow corona discharge was generated by applying a positive DC voltage to a rod-plane electrode in synthetic air. The changes in the gas temperature distribution due to the amplitude of applied voltage and the ambient gas pressure were investigated. Spectral images of a positive DC glow corona were taken using a gated ICCD camera with ultranarrow band-pass filters, corresponding to the head and tail of a N2 second positive system band (0–2). The qualitative gas temperature was obtained from the emission intensity ratio between the head and tail of the N2 second positive system band (0–2). From the results, we confirmed that the gas temperature and its distribution of a positive DC glow corona increased with increasing applied voltage. In particular, just before the sparkover voltage, a distinctly high temperature region was formed in the positive DC glow at the tip of the rod electrode. In addition, the gas temperature decreased and its distribution spread diffusely with decreasing ambient gas pressure.

Fast imaging of intermittent electrospraying of water with positive corona discharge

The effect of the electrospraying of water in combination with a positive direct current (dc) streamer corona discharge generated in air was investigated in this paper. We employed high-speed camera visualizations and oscilloscopic discharge current measurements in combination with an intensified charge-coupled device camera for fast time-resolved imaging. The repetitive process of Taylor cone formation and droplet formation from the mass fragments of water during the electrospray was visualized. Depending on the applied voltage, the following intermittent modes of electrospraying typical for water were observed: dripping mode, spindle mode, and oscillating-spindle mode. The observed electrospraying modes were repetitive with a frequency of a few hundreds of Hz, as measured from the fast image sequences. This frequency agreed well with the frequency of the measured streamer current pulses. The presence of filamentary streamer discharges at relatively low voltages probably prevented the establishment of a continuous electrospray in the cone–jet mode. After each streamer, a positive glow corona discharge was established on the water filament tip, and it propagated from the stressed electrode along with the water filament elongation. The results show a reciprocal character of intermittent electrospraying of water, and the presence of corona discharge, where both the electrospray and the discharge affect each other. The generation of a corona discharge from the water cone depended on the repetitive process of the cone formation. Also, the propagation and curvature of the water filament were influenced by the discharge and its resultant space charge. Furthermore, these phenomena were partially influenced by the water conductivity.

Physics of self-sustained oscillations in the positive glow corona

The physics of self-sustained oscillations in the phenomenon of positive glow corona is presented. The dynamics of charged-particle oscillation under static electric field has been briefly outlined; and, the resulting self-sustained current oscillations in the electrodes have been compared with the measurements from the positive glow corona experiments. The profile of self-sustained electrode current oscillations predicted by the presented theory qualitatively agrees with the experimental measurements. For instance, the experimentally observed saw-tooth shaped electrode current pulses are reproduced by the presented theory. Further, the theory correctly predicts the pulses of radiation accompanying the abrupt rises in the saw-tooth shaped current oscillations, as verified from the various glow corona experiments.

Gas Temperature of Steady Glow and Streamer Discharges in Atmospheric Air Gap

In order to analyze independently the various discharges of a point-to-plane air gap (steady glow, primary streamer, and secondary streamer discharges), the gas temperature in each of discharge region should be determined accurately by using the spectrum emitted from the second positive system bands of N2. In this experiment, we investigate the laser triggered streamer discharge with a repetition frequency of 10 Hz from the dc positive glow corona. The results show that the temperatures of the glow, primary streamer and secondary streamer are in the range of 316∼356K, 335∼350K and 370∼390K, respectively, and are considerably lower than the value of the high-stable dc positive repetitive streamer corona published in the previous references.

Charging of Polymeric Surfaces by Positive Impulse Corona

This paper focuses on analysis of charging of polymeric surfaces by means of impulse corona discharges in air. Internal (space charge densities and electric fields) as well as external (circuit current) characteristics of corona in a point-plane electrode configuration are investigated by means of computer simulations. Two types of onset positive corona modes, namely positive glow corona and burst pulse corona are identified. The developed and verified computer model is further used to study corona charging of a 2 mm thick polymeric material sample. Both the mechanism of charge deposition and distribution of deposited charges on the surface are dependent on the mode of the corona discharge used. In the case of glow corona, charge generation is limited to the anode region and the generated charges move towards the sample surface under applied electric field. Thereafter the deposited charge cloud expands radially along a portion of the surface with fairly constant concentration. In the case of burst pulse corona, series of positive charge clouds start from the anode and move towards the sample surface in a wave-like manner. Each burst contributes to the deposited charge, which spreads over the surface less extensively than that observed during glow corona charging.

On the fluctuations in positive glow corona

Current knowledge of fluctuations in the steady glow current of the positive rod-to-plane corona at normal air density is reviewed. New work has been extended to investigate how the frequency and amplitude of these fluctuations change with the air density and humidity. The air density has been changed both by decreasing the pressure and by increasing the temperature. The pressure has been decreased down to 0.6 bar, and the temperature has been increased up to 200 degrees C. A method is proposed for calculating the frequency of fluctuations in any rod-plane gap with known field distribution. The method is based on assessment of the space charges developed in a positive glow corona that fill not only the ionisation zone around the rod but also the inter-electrode spacing. These space charges result in an electric field that affects the frequency of these fluctuations. The calculated frequency values agree reasonably with those measured for different rod diameters.

Onset voltage of positive glow corona in rod-plane gaps as influenced by temperature

The postulate put forward by Hermstein to account for the positive glow corona was widely accepted at first and later criticised. Loeb's alternative postulate has not been fully satisfactory. In this paper, a method is described for calculating the onset voltage of positive glow corona in rod-plane gaps in air at room and high temperatures. The method has a flavour of both the Hermstein and Loeb postulates, but is based on the physics of air discharges occurring in the ionisation zone around the stressed rod. The threshold voltage of onset streamers and their development at higher voltages are prerequisites for calculating the onset voltage of positive glow. The threshold and onset voltages increase with the gap spacing at room temperature and decrease with the increase of air temperature for the same gap geometry in conformity with previous findings. The calculated threshold voltage and repetition rate of onset streamers, in addition to the onset voltage of the positive glow agree reasonably with those measured experimentally.

The effect of corona discharge on Der p 1.

Reduction of house dust mite allergens in the domestic environment can play an important part in reducing sensitization and in the amelioration of symptoms in atopic individuals. Chemical and physical methods have been tried with varied levels of success. The present paper presents a novel electrostatic way of destroying Der p 1, the major mite allergen. To assess the efficacy of negative Trichel, negative continuous glow, positive pulse and positive continuous glow corona in destroying Der p 1. To determine whether ozone has any effect on the integrity of Der p 1 in the experimental conditions present. A simple point-to-plane apparatus was used to irradiate samples of Der p 1 for periods of 1, 15, 30, 45, 60, 120, 180, 240 and 300 min. Controls were exposed to the atmosphere with no corona products present for the equivalent time. The effect of the corona by-product ozone was investigated alone by exposing samples of Der p 1 to molecular ozone for 60 min. Der p 1 concentration was quantified by two-site monoclonal antibody ELISA. High current negative glow resulted in a 67.37% reduction in Der p 1 concentration after 300 min compared with a 50.5% reduction from a low current Trichel regime. High current positive glow corona gave a reduction of 25.22% while a low current positive pulse corona caused a 13.72% reduction after 300 min. All these reductions were statistically significant (P < 0.05) compared with unexposed controls. Negative corona always gave greater percentage reductions in Der p 1 concentration for each time exposure investigated. The pattern of percentage reduction follows an exponential rise to maximum relationship in respect to time. Samples of Der p 1 were not affected by exposure to molecular ozone. These data indicate corona products to be a powerful new method of destroying Der p 1 allergen that is not dependent on the presence of the oxidizing corona product ozone.

Charge-carrier extraction from air and nitrogen gas streams that entrain charge from dc corona ionizers

Charge decay upon a pre-charged target was studied in a gas flow channel that contained a pair of point-to-plane corona-discharge emitters. Charge decay was primarily determined by charge carriers entrained from the negative corona discharge and gas flow. The positive glow corona removed excess negative carriers and added positive carriers to achieve balanced residual charge on targets. Discharge modes with extended structures, such as streamers in air and nitrogen and sparking, yielded positive and negative charge carriers that were most likely to be entrained. The magnitudes of corona currents in ionizers were of lesser importance.

Self-oscillations of a positive corona in nitrogen

The oscillatory behaviour of a glow positive corona in pure nitrogen is observed experimentally. The regular self-oscillations of the corona current and the light emission from the glow ionization region, as well as the averaged volt-ampere characteristics of this discharge, are studied comprehensively within gas pressure range 10-765 Torr. It is revealed that the positive glow corona generates a soft x-radiation. This radiation plays a crucial role in the photo-ionization of nitrogen. Furthermore, it provides a fast positive feedback for electron avalanches through the ionization region of the corona. The results of numerical modelling of the glow corona under free-running oscillations are also presented.

The theory of positive glow corona

A theory for the current and light pulses of positive glow corona from a point in air is presented; this phenomenon was first observed as an apparently continuous glow by Michael Faraday. Results are obtained, in concentric sphere geometry, for air at atmospheric pressure, by solving the continuity equations for electrons, positive ions, negative ions and metastable oxygen molecules, coupled with Poisson's equation. A series of `saw-toothed' current pulses of period about is predicted with a DC current level. Accompanying the current peaks are discrete pulses of light 30 ns wide. Successive `shells' of positive ions, from successive current pulses, carry 96% of the mean current. The mean current - voltage relationship has the classic square-law form. The seed electrons required for successive pulses are detached from negative ions by metastable oxygen molecules. Photo-ionization is crucial for the discharge at the anode and for the formation of negative ions throughout the gap. The pulse frequency varies with applied voltage and is found to be approximately proportional to the positive-ion mobility. The surface electric field at the central electrode remains close to Peek's onset field. The origin of onset streamers is explained and sub-microsecond voltage pulses are found to produce streamers. The results for concentric-cylinder electrodes are described briefly.

The Oscillations of the Positive Glow Corona

The paper treats experiments, computer simulations, and the physical explanation of the oscillatory behaviour of positive glow coronas at or below atmospheric density. Experiments show that most positivc glows have ionization regions that oscillate with frequencies depending on the gas, geometry, and average discharge current. Our circuit simulating program CIRCSIM with the general gas discharge elemcnt GPCSI reproduces quantitatively Beattie's sphere-to-plane coronas in air, and also our cylindrical coronas in air and in argon with additives. The oscillations demand a fast secondary ionization (feedback) mechanism, and are damp or inhibited by slower feedback processes like positive ion or metastable feedback, and detachment from negative ions. Linear damp oscillations are due to ionization region capacitance and equivalent inductance. Nonlinear self-sustained oscillations are formed by periodic quenching by the generated positive ions.

Breakdown characteristics of cryogenic gaseous helium in uniform electric field and space charge modified non-uniform field

D.c. breakdown characteristics of gaseous helium in uniform and non-uniform electric fields down to 4.2 K at atmospheric pressure have been investigated. Although helium is a nonelectronegative gas, a negative pulse corona is observed only near the normal boiling point due to the abrupt appearance of quasi-bubble state electrons. Positive ion space charge modifies the electric field distribution in the gap space considerably. The electric field strength on the non-corona electrode in the ion flow field is measured satisfactorily and analysed theoretically using a numerical electric field calculation technique. On the basis of experimental results, methods are proposed to give corona onset criteria and the breakdown voltage preceded by a positive glow corona.