Air Corona Research Articles

Theory of stability of self-sustaining dc discharges at inception with application to negative corona.

The inception of self-sustaining dc discharges is analyzed in terms of the bifurcation theory. The existence of a nonphysical solution with negative ion and electron densities must be taken into account in order to identify the bifurcation type. The bifurcation is transcritical for positive and negative corona discharges and, in more general terms, it is expected to be transcritical for all discharge configurations except for the parallel-plate discharge, where the bifurcation is pitchfork. General trends of the bifurcation theory suggest that the corona discharges should be stable immediately after the inception. This conclusion is tested numerically for negative coronas in atmospheric-pressure air in coaxial-cylinder geometry. Two independent approaches have been used: (1) study of linear stability against infinitesimal perturbations with the use of an eigenvalue solver, and (2) following the time development of finite perturbations with the use of a time-dependent solver. The numerical results agree with each other and with the theory. In particular, it is shown that the negative corona is stable, i.e., pulseless, immediately after the ignition. The loss of stability occurs through growth of harmonic perturbations, which subsequently evolve into Trichel pulses, and this happens on the ascending branch of the current-voltage characteristic, contrary to the popular concept of negative differential resistance. Results of the work are of theoretical interest and offer further insights into physics of negative corona discharges.

The Evolution Study of Positive Corona in Atmospheric Air Based on the Combination of Light Radiation and Discharge Current

The Evolution Study of Positive Corona in Atmospheric Air Based on the Combination of Light Radiation and Discharge Current

New insight on filamentary charge‐loaded flows originated by pulsating glow‐type unipolar coronas in atmospheric air

AbstractThe diffusional process involving elastic collisions between charge carriers and neutrals has long been the predominant candidate for post‐injection momentum loss in the far wider drift region outside confined DC corona discharges in gases. A supplementary research paradigm is here put forward for the interest of a greater understanding of corona‐assisted unipolar ion flows in atmospheric air. In this respect, the auto‐pulsing mode of glow‐type coronas in air is modelled as a source of momentum whose conservation is substantially preserved across the external transfer region. The tangible prospect of charge‐bearing flows in the form of a filamentary convection, with negligible drifting component, in buffer gas is put forward in relation to spontaneous symmetry‐breaking instability. This setting bears some resemblance to the self‐organised collective behaviour of self‐propelled (active) particles. The value of this scheme gains strength precisely in relation to the strong inhomogeneity of the electric field surrounding electrodes prone to go into corona. On such a basis, it is believed that the drift of corona‐generated ions deserves to be reconsidered in view of the arguments set out in the present modelling.

Investigation of conditions necessary for inception of positive corona in air based on differential formulation of photoionization

Sharp point electrodes generate significant electric field enhancements where electron impact ionization leads to the formation of electron avalanches that are seeded by photoionization. Photoionization of molecular oxygen due to extreme ultraviolet emissions from molecular nitrogen is a fundamental process in the inception of a positive corona in air. In a positive corona system, the avalanche of electrons in the bulk of the discharge volume is initiated by a specific distribution of photoionization far away from the region of maximum electron density near the electrode where these photons are emitted. Here, we present a new approach to finding the inception conditions for a positive corona, which is based on a differential formulation of the photoionization problem. The proposed iterative solution considers the same inception problem that has been solved in the existing literature by using either an integral approach to photoionization or a differential formulation of photoionization and considering the inception problem as a boundary-value eigenvalue problem. The results are validated by comparisons with previous integral formulations and time dynamic plasma fluid solutions in planar and spherical geometries. The results illustrate ideas advanced in Kaptzov (1950 Elektricheskiye Yavleniya v Gazakh i Vacuume p 610) providing a physically transparent connection between an effective secondary electron emission coefficient due to volume photoionization in a positive corona system and the secondary electron emission in conventional Townsend discharge theory. The results also demonstrate the significance of boundary conditions for accurate corona solutions that are based on a differential formulation of photoionization.

Role of air pollution on COVID-19 in Istanbul

There are many types of research on strong relations between air pollution and the respiration system. This paper is related to the effect of air pollution on pandemic case numbers. By analyses of the number of patients and mean air pollution (µg/m³) data by using data mining, it is concluded that there was evidence of this relationship with a significant level alpha = 0,10. This paper estimates "the number of patients with coronavirus" as a function of daily air pollution and corona case numbers data using single ANN, LSTM, and W-ANN, W-LSTM hybrid methods. This paper explains small, meso, and large scale factors and their role on COVID-19 patients. This finding does not demonstrate a direct cause-effect relationship between air pollution and COVID-19 patients. This study shows the importance of pollution on the number of patients with COVID -19 infection. Although our results have significant uncertainties, we can clearly distinguish the contribution of air pollution to COVID-19 patients. When we used wavelet transformation of air pollution data to estimate COVID-19 patient’s numbers, R2 score is increased in both ANN and LSTM between [0.01- 0.10]. Nevertheless, the actual number of patients is influenced by many additional factors such as the country's health system. After error analysis, sMAPE [3.6-5.9] changed, there is sufficient evidence of model results (M3, M4 Hybrid LSTM) and observation. (0.91

Electric charge build-up and dissipation at pulsed streamer corona by EFISH and probe measurements

This work examines the dynamics of volumetric electric charge deposited by a single pin electrode streamer corona in atmospheric air at ambient conditions. Recent studies show that, at pulse-periodic operation, electric charge remains in surrounding air after the first discharge. This residual charge significantly affects the electric field distribution and morphology of discharges at subsequent pulses. In this study, the residual electrical potential/field was measured during and after dissipation of a pulsed 80 kV streamer corona of alternating polarity. This was accomplished using electrostatic probes and the electric field induced second harmonic method (EFISH generation). The residual volumetric charge of a positive pulse polarity streamer corona occupies a zone of up to 80 mm from the electrode. The subsequent application of a negative polarity pulse leads to partial neutralization of the previous charge and the generation of a region with a high-amplitude electric field. The propagation of following positive polarity pulses is limited by the residual positive volumetric charge. The EFISH method reveals the magnitude of the electric field at discharge propagation and electrostatic probes inform the polarity. Intensified imaging acquisition was used to evaluate the spatial distribution and dynamics of corona discharge during the alternating polarity waveform.

Electric field measurements of DC-driven positive streamer coronas using the E-FISH method

This paper reports on electric field measurements, using the electric field-induced second harmonic (E-FISH) method, sampling the spatial structure and temporal development of DC-driven positive streamer coronas in atmospheric-pressure air at relevant timescales to examine the self-pulsating behavior of the discharge. The discharge is triggered from a point-to-plate geometry and consists of transient coronas, which bridge the inter-electrode gap and pulsate at about 3 kHz, superimposed with a persisting glow corona. The measurements presented challenge the phenomenological explanation for the pulsations based on field recovery at the anode driven by the evacuation of positive ions by electric drift effects and hint at a propagating wave-like feature from the plate-cathode to the tip-anode.

High temperature coronas in air and flue gas from LPG combustion: Current-voltage characteristics, ion mobilities and free electrons

Positive and negative corona discharges were studied at atmospheric pressure in a tube-wire geometry with a tube diameter of 150 mm. Current-voltage characteristics (CVCs) were measured both in air and in flue gas produced with a liquefied petroleum gas (LPG) burner, covering temperatures from ambient up to 1073 K. Corona operation was stable over the whole temperature range with positive polarity and up to 973 K with negative polarity. Based on a detailed analysis of the original CVC measurements, new insights on the temperature-dependent mobility of gas ions, on the occurrence of free electrons and on the electronic current contribution are presented. Deviations from the Townsend theory of CVCs can be ascribed to the lifetime-dependency of ion mobility caused by the formation of cluster ions. The contribution from free electrons is found to depend on temperature and tube radius.

Fundamental investigation of unipolar and RF corona in atmospheric air

Unipolar (DC) and radio frequency (RF) corona at 3.3 MHz is studied at centimeter-sized gaps in a needle-plane geometry in atmospheric air at room temperature. Positive and negative corona using pure tungsten electrodes with varying tip angles revealed a lower onset voltage for the needle with the smaller included angle. The RF corona onset voltage and corresponding time delay were measured for a series of needles composed of pure tungsten or 2% lanthanated tungsten. The corona onset, established when the first instance of UV photon emission is detected via photomultiplier tube, occurred primarily during the negative half cycle of the applied RF voltage for pure tungsten needles. In contrast, with lanthanated tungsten needles, such preference was not observed. No distinguishable difference in onset voltage between pure tungsten and lanthanated tungsten was found, indicating that adding a small amount of lanthanum to tungsten has a negligible impact on the onset voltage at 3.3 MHz frequencies for electrodes at room temperature.

Visualization of Activated Area on Polymers for Evaluation of Atmospheric Pressure Plasma Jets

The treatment of a polymer surface using an atmospheric pressure plasma jet (APPJ) causes a local increase of the surface free energy (SFE). The plasma-treated zone can be visualized with the use of a test ink and quantitatively evaluated. However, the inked area is shrinking with time. The shrinkage characteristics are collected using activation image recording (AIR). The recording is conducted by a digital camera. The physical mechanisms of activation area shrinkage are discussed. The error sources are analyzed and methods of error reduction are proposed. The standard deviation of the activation area is less than 3%. Three polymers, acrylonitrile butadiene styrene (ABS), high-density polyethylene (HDPE), and polyoxymethylene (POM), are examined as a test substrate material. Due to a wide variation range of SFE and a small hydrophobic recovery, HDPE is chosen. Since the chemical mixtures tend to temporal changes of the stoichiometry, the pure formamide test ink with 58 mN/m is selected. The method is tested for the characterization of five different types of discharge: (i) pulsed arc APPJ with the power of about 700 W; (ii) piezoelectric direct discharge APPJ; (iii) piezoelectric driven needle corona in ambient air; (iv) piezoelectric driven plasma needle in argon; and (v) piezoelectric driven dielectric barrier discharge (DBD). For piezoelectrically driven discharges, the power was either 4.5 W or 8 W. It is shown how the AIR method can be used to solve different engineering problems.

Consideration of the Insulation Design Method on a ±200 kV Converter Valve Unit in an HVDC Converter Hall

A converter valve unit, which converts Alternating Current (AC) to Directing Current (DC) and DC to AC, is one of the key elements of high voltage direct current (HVDC) transmission. The insulation design of a converter valve unit should be considered for air clearance according to the DC superimposed overvoltage and the insulator that maintains the insulation performance and the corona shield to suppress DC corona discharge. There is no prescribed standard for the insulation design of a converter valve unit. Moreover, insulation performance under an applied DC voltage has not yet been thoroughly investigated. Therefore, it is necessary to study the insulation design method of the converter valve unit. In this paper, consideration of the insulation design method on a ±200 kV converter valve unit in an HVDC converter hall is performed. The finite element method (FEM) is used to simulate the 3D model. Additionally, the safety factor (SF) is applied in accordance with the dielectric test in IEC 62271-1. As a result, an insulation design process on the converter valve unit is proposed and the insulation design is carried through the design factors. It is confirmed that design factors on the air clearance, insulator and corona shield have a significant effect on a highly reliable insulation design.

Gas temperature spatial distribution in air corona discharge with plane comb of metal rod electrodes derived from schlieren images

Gas temperature fields in the air corona discharge with a plane comb electrode system have been determined for the negative and positive polarities of the applied voltage. Highly sensitive schlieren technique used in the study allowed detecting a temperature change in tenths of a degree centigrade at room temperature of the gas flow. The obtained results suggest that the gas in the studied electrode system does not undergo heating at the given range of working parameters.

Corona with Streamers in Atmospheric Pressure Air in a Highly Inhomogeneous Electric Field

The paper presents research data on positive and negative coronas in atmospheric pressure air in a highly inhomogeneous electric field. The data show that irrespective of the polarity of pointed electrodes placed in a high electric field (200 kV/cm), this type of discharge develops via ball streamers even if the gap voltage rises slowly (0.2 kV/ms). The start voltage of first positive streamers, compared to negative ones, is higher and the amplitude and the frequency of their current pulses are much lower: about two times and more than two orders of magnitude, respectively. The higher frequency of current pulses from negative streamers provides higher average currents and larger luminous areas of negative coronas compared to positive ones. Positive and negative cylindrical streamers from a pointed to a plane electrode are detected and successive discharge transitions at both polarities are identified.

Emission Spectrum Analysis of Two Typical Partial Discharge Forms Under High Frequency Square Wave Voltages

Although the increase in frequency improves the transmission efficiency of high-frequency transformer, a higher probability of insulation failure is caused by high-frequency partial discharges. Through a high-frequency experimental platform, emission spectrum tests on two types of insulation faults were carried out under high-frequency square wave voltages. Subsequently, the influence of frequency and voltage amplitude on the light intensity and the number of photons of emission spectrum caused by air corona were studied. Finally, the variation of the spectrum of the partial discharge occurring at the interface of gas-solid insulation with frequency was analyzed. The results show that, the characteristic spectrum of air corona is composed of the near-ultraviolet spectrum, which is caused by the energy level transition of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> molecules, and the number of photons of air corona is positively correlated with voltage amplitude and frequency. Partial discharges at the gas-solid insulation interface have band spectrums in the visible light region and the near-infrared light region except for the near-ultraviolet spectrum due to the energy level transitions of outer layer electronics and the vibrations of C-H chemical bonds of PET molecules. This paper preliminarily verified the feasibility of applying the emission spectrum diagnostic method to two typical partial faults under high-frequency square wave voltages.

Pulsation Characteristics of Corona Discharge in Electrohydrodynamic Process Using Ionic Liquid

In this study, the pulse phenomenon is found in the electrohydrodynamic (EHD) process using an ionic liquid, which is similar to other liquids, but there are significant differences in pulse characteristics. The frequency, waveform, charge, and images of the pulse in the EHD process with the ionic liquid are studied experimentally. The results show that the pulse process is divided into two stages: a low-frequency pulse stage and a high-frequency pulse stage. We propose that the pulse is caused by the air corona discharge and the frequency is influenced by the anchoring radius of liquid oscillation in the electric field. The different anchoring radii of the two stages are the main reason for the obvious difference in the frequency. The main difference between the ionic liquid and other solutions is the conductivity and the surface tension coefficient, which is the cause of corona discharge rather than electrospray.

The pre-breakdown characteristics of weakly ionized media in the high non-uniform electric field

The theoretical model of pre-breakdown ions formation in a liquid dielectric and their flows, caused by high non-uniform electric field is represented. The 3D system of macroscopic pre-breakdown electrohydrodynamic equations is written. The electric field influence on the molecule dissociation rate is taken into account. The system are included the Poison equation for electric field potential, equation of ions formation and Navier-Stokes equations with electric force The our up-steady analytical electrodynamic solution of these equations for potential of electric field distribution at spherical high voltage capacitor with liquid transformer oil type dielectric is described deviations from Ohms law, observed in many experiments. The analytical non-stationary solution for velocities distributions calculations of considerable liquid dielectric flows are obtained. The theoretical and experimental micro-breakdown radius zone dependences on applied voltage at air corona discharge are obtained for edge high voltage electrode.

From Switching Arcs to Ball Lightning to Curing Cancer!

Previous modelling of switching has been through calculation of reductions in temperature of the arc at "current zero". "Enthalpy density" as a function of temperature is found to be an important property. New calculations now include an account of non-equilibrium electron density as a function of time through current zero and it is found that electron attachment rates, which are very large for SF6, could be a dominant property. Modelling discharges is having other successes, for example in explaining "ball lightning" observations inside of houses and aircraft, which suddenly appear, usually at glass windows. Discharge modelling suggests these observations might be explained by the production of "singlet delta" metastable molecules of oxygen in electrical discharges in air. If metastable densities are sufficient, electrons can be produced from the detachment of negative ions to produce radiation and explain ball lightning. An exciting new development is that plasmas from electric corona in air have been found to reduce the size of cancer tumours. These excited oxygen molecules have also been proposed as having a role in this remarkable interchange between classical electrical engineering and medical science.

The Initial Stage of Diffuse Jet Formation in a Pulsed Discharge with a Non-Uniform Electric Field in Air

Laboratory simulation of the conditions for the occurrence of blue jets in the Earth’s atmosphere has been carried out. For this purpose, the diffuse formation of jets and plasma buildup in corona and apokampic discharges in air has been studied. It is shown that the jets are formed due to streamer breakdown and their color depends on air pressure. At atmospheric air pressures of 30–120 Torr, streamers starting from different parts of a repetitively pulsed discharge are recorded in a nonuniform electric field. It has been ascertained that a spherical corona discharge is formed before a breakdown between pointed electrodes, near a metal high-voltage electrode of positive polarity, from which streamer coronas start as the voltage increases. Data on the streamer head size and streamer propagation speed in the corona and apokampic discharges are presented.

Electrical equivalent circuit and modeling of a pulsed air corona discharge

In this paper, we present an equivalent circuit model of a multi filamentary corona discharge powered by pulsed positive voltage in the case of humid air at atmospheric pressure. The elements of the equivalent circuit are obtained by an optimization method of parameter identification, applying the Recursive Least Square algorithm with a Variable Forgetting factor (RLS-VF), based on the measured currents and voltages of the discharge. A comparison between the measured discharge current and the calculated current shows a good agreement. The obtained time varying discharge resistance is between about 5–300 mΩ and the capacitance between about 0.01 pF to 1 pF. Then we used the equivalent circuit components to calculate the energy efficiency versus the applied voltage that varies at its maximum under the present experimental conditions from about 20% to 50%.

Peak and Average Power Handling Capability of Microstrip Filters

In this paper, the power handling capability of microstrip filters is studied in detail. This paper is addressed from two perspectives, depending on the physical phenomenon limiting the maximum power that the microstrip filter can handle. One of these phenomena is air breakdown or corona effect, which is linked to the peak power handling capability (PPHC) of the device, and the other is the self-heating, which limits the device average power handling capability (APHC). The analysis is focused on three kinds of filtering topologies widely used both in academia and industry, such as the coupled-line, stepped impedance resonator and the dual-behavior resonator-based filters. Closed-form expressions are computed to predict both the PPHC and the APHC as a function of the geometrical parameters of the resonators integrating the filter. Guidelines are also given to extrapolate the provided computations to other filtering topologies based on other kinds of resonators. To validate this research study, three bandpass filters centered at 5 GHz have been implemented and fully characterized by means of two measurements campaigns which have been carried out, one for the PPHC and another one for the APHC. The measured results have validated the performed study and corroborated the conclusions obtained throughout this paper.