Corona Current Research Articles

A Single-Species Pulsed Model of Negative Corona Discharge in Air

This paper presents a new dynamic model for the negative corona discharge in the point-plane geometry. The hybrid boundary-element-finite-element method technique is used to calculate the electric-field parameters, and the method of characteristics is employed for the charge-transport prediction. The simulation results show the charge-density distributions in the air gap and along the axis of symmetry, and the total corona current, for different voltage waveforms and parameters of the electric circuit.

Patterns of Needle-Plane Discharges in Electronegative Hydrocarbons

Some of our previous experimental work focused on corona discharges in hydrocarbon media. It has been shown that the discharge can be characterized by corona “impedance.” The present article elaborates on this work and introduces complementary details. In a negative pin-to-plane geometry, the experiments show that a corona parameter exhibits quasi-linear variation with corona current. The discharge was studied in a medium with controlled pressure, temperature, and homogeneity of the sample. The results were reproducible on different concentrations of the hydrocarbon mixture used. A modeling of the observed phenomenological relation is discussed. It is believed that the present analysis can be useful in optimizing characteristics of pin-plane corona discharges in hydrocarbon media.

Influence of cathodic protection and transmission-line proximity on oil-flow electrification

Two reduced-scale closed oil cycles are used to investigate the influence of both the cathodic protection of a pipeline and its proximity to AC power transmission lines on the oil-flow electrification (OFE). For the former case, the results reveal that the OFE is highly dependent on the magnitude of the protection current. The higher the protection voltage the higher is the OFE. Also, the results show that the OFE is enhanced by oil velocity and/or temperature. For the latter case, the results indicate that conductor bundling has a monumental impact on all measured quantities: pipe floating potential, and both corona and streaming currents. In addition, oil temperature causes evident quantitative as well as qualitative changes in the measured streaming current, but no effect was found on both pipe floating potential and corona current. The results are interpreted in terms of physico-chemical and electrochemistry point of view together with electric field computation using a program based on charge simulation method.

Electric fields and corona currents in needle-to-meshed plate gaps

This paper is aimed at evaluating the electric field, the corona onset voltage and the corona current in negatively stressed needle-to-meshed plate gaps as compared with the case of using a flat plate. The charge simulation method is used for calculating the electric field in the gap. The onset voltage is evaluated based on the calculated field and the criterion for self-recurring single electron-avalanches in the ionization-zone around the needle tip. The corona current–voltage characteristics were measured for thin and thick needles at two gap spacings with meshed and flat plates. The corona currents with meshed plates are lower than those with a flat plate; even the corona onset voltage with the flat plate is higher than that with the meshed plate.

Corona performance of conductor-to-plane gaps as influenced by underneath grounded and negatively stressed metallic grids

This paper is aimed at investigating how the positive dc corona performance of conductor-to-plane gaps is influenced by grounded and negatively stressed metallic grids located underneath the coronating conductor. A systematic experimental study is made to investigate the corona current–voltage characteristics and the current density distribution at the ground plane with and without grid. The wire-to-wire spacing, number, lateral distribution and height of grid wires as well as the conductor diameter are varied. The current density distribution at the ground plane is correlated with Warburg law that was proposed for point-plane coronas.

Electrical analysis of positive corona discharge in air and N2, O2, and CO2 mixtures

This paper presents an experimental analysis of the electrical behavior of positive point-plane corona discharges. The corona current, streamer velocity, mean discharge frequency, and current-voltage characteristic are studied, firstly in synthetic air as a function of experimental parameters such as gap distance and tip radius. Different electrical diagnostics are used in order to better understand the streamer development as well as the dependence of its characteristics on the previous listed parameters. Then the influence of gas mixture (several proportions of N2 and O2 with or without CO2) is analyzed. When the gas concentration is varied the shape and amplitude of the corona current are significantly affected due to the variation of the gas electronegativity following its composition and concentration. The ionization and attachment coefficients are calculated from the electron energy distribution function in the case of these different gas mixtures in order to quantify the critical electric field value enabling the streamer development for a given gas mixture.

Equivalency of Lightning Return-Stroke Models Employing Lumped and Distributed Current Sources

We show that any engineering return-stroke model can be expressed, using an appropriate continuity equation, in terms of either lumped or distributed current sources with the resultant longitudinal-current distribution along the channel being the same. This property can be viewed as the duality of engineering models. The conversion alters the actual-corona current (if any) of the model. For lumped-source (LS) models the actual-corona current is unipolar and directed radially out of the channel core, while for distributed-source (DS) models it is unipolar and directed into the channel core. For LS models converted to DS models and for the Diendorfer-Uman (DU) model converted to the equivalent LS model, the corona current is the sum of the negated actual-corona current (if any) and a fictitious-corona current, the latter being bipolar. For the transmission-line (TL) model (no longitudinal current attenuation with height) expressed in terms of DSs, there is only a fictitious bipolar corona current component. Conversion of the traveling-current source (TCS) and Bruce-Golde (BG) models to equivalent LS models involves replacement of the actual, unipolar corona current with a fictitious one, the latter current being bipolar near the channel base and unipolar at higher altitudes

An Ozone Fan Utilizing Pin-to-Plate Corona Discharge Field

Experimental and theoretical research has been conducted to investigate basic characteristics of an ozone fan utilizing the ionic wind induced in the pin-to-plate corona discharge field. When a high voltage was applied between the electrodes, the ionic wind, which included ozone, flowed from the pin elecrode to a hole of the plate electrode. It was deduced that (1) the ozone concentration is almost linear with respect to the corona current, (2) the ozone concentration was high with the large pin diameter but almost irrelevant with the gap between the electrodes, (3) the energy efficiency of the negative corona was about 14 times higher that of the positive corona, but it was only several %, (4) the ozone generation was reduced at high temperature. It was estimated that the several ppm ozone could be generated and flowed utilizing the negative discharge and the ozone generation was almost eliminated by turning off the polarity.

A study of the lightning channel corona sheath

Dynamics of lightning channel corona sheath surrounding thin channel core is examined on the basis of three transmission‐line‐type models of the return stroke that specify different attenuation of longitudinal current with height. The corona sheath conductivity is estimated using measured radial electric field in the immediate vicinity of the lightning channel and measured channel base current. The corona sheath radius, velocity of corona sheath radial expansion, and corona current are examined using a multiexponential approximation of the lightning channel base current waveform. Additionally, energy dissipated in the corona sheath is estimated and compared to that dissipated in the channel core.

Corona Emission and Ozone Production by Carbonized and Oxidized High-Voltage Wires

High-voltage wires exhibit corona discharges that cause emission of ozone. Precipitation, dirt, and wire imperfections have been shown in earlier works to increase both processes by a factor of up to 50. Here, a small coaxial cylinder setup is used to quantify the effects of volatile organic atmospheres and wire oxidation on corona and ozone production. With both positive and negative dc, corona initiation voltages can be lowered by a factor of about 4 in the presence of flake-forming chemistry, accompanied by very large increases of corona current. These results all fit the simple Cobine and Townsend model, which permits extrapolation of our corona current measurements to different wire conditions. Ozone generation rates were measured with ozone test papers in a sealed setup. Approximately 25 ozone molecules per corona electron were obtained from a negative oxidized copper wire at 24 kV.

Comparison Between an Unipolar Corona Charger and a Polonium-Based Bipolar Neutralizer for the Analysis of Nanosized Particles and Biopolymers

In this work we present results on the charging efficiency of nanoparticles by means of a corona based unipolar charging unit. This device was designed to replace a Po210 bipolar charger unit in a commercial electrospray aerosol generator (TSI Mod 3480). The charging efficiency has been investigated for negative and positive charged particles of various chemical composition in the size range between 5 and 18 nm. The corona current has been found to be the most influential operation parameter on the charging efficiency. With a positive electrospray droplet charge and a negatively-biased corona needle, a rapidly decreasing yield of singly positively charged aerosol particles with increasing corona current was found. An increasing yield of negatively charged particles was observed with increasing current of the corona process. Providing appropriate corona settings nanoparticles with charge levels similar to these obtained with a Po210 charger were found. At optimal corona settings the yield of singly charged particles was found to be two to four times higher for negative and positive particles compared to bipolar charging. This gain in the charging efficiency increases directly the sensitivity of analysis and enhances all measurement and manipulation processes of airborne nanoparticles for which electrical charging is required.

Numerical simulations of thunderstorm-induced corona processes near lightning rods installed on grounded structures

For the purpose of estimating the efficacy of a lightning rod, the current of a corona was numerically calculated from a rod placed (i) centrally on the roof of a vertical grounded cylindrical structure, a model of a man-made object, and (ii) at the top of a grounded hemispherical structure of large radius, such as a hill or mountain. The calculations were carried out for a slowly varying thundercloud electric field and when this field was enhanced by the charge of an approaching downward leader. In case (i), variation of the ratio between the height and radius of the cylindrical structure leads to a variation in the (a) corona current from the tip of the rod over a wide range and (b) distance from which lightning is attached to the rod. In case (ii), it is shown that, contrary to the case of rods installed on the ground surface, a slowly rising thundercloud electric field can be sufficient to initiate streamers and upward leaders from rods tens of meters in height installed on the top of tall, grounded, hemispherical structures. When the thundercloud electric field is enhanced by the charge of an approaching downward leader, the discharge processes near the rod depend on its length and the height of the tip of the downward leader relative to the top of the hemispherical structure, but are almost independent of the hemisphere radius.

Electrohydrodynamic Enhancement of Heat Transfer for Developing Air Flow in Square Ducts

Corona discharge in air was used to generate a secondary flow that significantly improved the convective heat transfer coefficient in the developing region of a square duct. A wire electrode, charged with a high voltage, was placed at the center of the duct. The electrode ionized the air and created a corona current, which was measured experimentally and used in the computations. The conservation differential equations for flow, energy, and electric field were considered for the 3D flow in the developing region of the duct, and they were solved numerically. The computational results indicated that the secondary flow gradually evolves into a fully-developed eight-cell vortical structure that creates flow mixing and turbulence and enhances the heat transfer coefficient. In this study, the ranges of Reynolds number and applied voltage were 500–10,000 and 0–11.7 kV, respectively. The normalized Nusselt number, Nu/Nuo, ranged from 1.06 (Re = 10,000 and 8.1 kV) to 13.58 (Re = 2000 and 11.7 kV), but the pressure drop penalty was relatively low. The normalized friction factor, f/fo, ranged from 1.01 (Re = 10,000 and 8.1 kV) to 7.28 (Re = 2000 and 11.7 kV). The computations were verified by comparison with the published literature.

Expansion of Substrate Specificity of Cytochrome P450 2A6 by Random and Site-directed Mutagenesis*

The natural product indole is a substrate for cytochrome P450 2A6. Mutagenesis of P450 2A6 was done to expand its capability in the oxidization of bulky substituted indole compounds, which are not substrates for the wild-type enzyme or the double mutant L240C/N297Q, as determined in our previous work (Wu, Z.-L., Aryal, P., Lozach, O., Meijer, L., and Guengerich, F. P. (2005) Chem. Biodivers. 2, 51-65). Error-prone PCR and site-directed mutagenesis led to the identification of two critical amino acid residue changes (N297Q and I300V) that achieve the purpose. The new mutant (N297Q/I300V) was able to oxidize both 4- and 5-benzyloxy(OBzl)indoles to form colored products. Both changes were required for oxidation of these bulky substrates. The colored product derived from 5-OBzl-indole was mainly 5,5'-di-OBzl-indirubin, whereas the dominant blue dye isolated upon incubations with 4-OBzl-indole was neither an indigo nor an indirubin. Two-dimensional NMR experiments led to assignment of the structure as 4-OBzl-2-(4'-OBzl-1',7'-dihydro-7'-oxo-6'H-indol-6'-ylidene)indolin-3-one, in which a pyrrole ring and a benzene ring are connected with a double bond instead of the pyrrole-pyrrole connection of other indigoids. Monomeric oxidation products were also isolated and characterized; three phenols (4-OBzl-1H-indol-5-ol, 4-OBzl-1H-indol-6-ol, and 4-OBzl-1H-indol-7-ol) and one quinone (4-OBzl-1H-indole-6,7-dione, the postulated immediate precursor of the final blue dye) were identified. The results are interpreted in the context of a crystal structure of a P450 2A6-coumarin complex. The I300V change opens an additional pocket to accommodate the OBzl bulk. The N2297Q change is postulated to generate a hydrogen bond between Gln and the substrate oxygen. Thus, the substrate specificity of P450 2A6 was expanded, and new products were obtained in this study.

Corona discharge in the hyperbolic point-plane configuration: direct ionization criterion versus approximate formulations

The paper presents an algorithm to simulate the electric corona discharge in the two-dimensional hyperbolic needle-ground plate configuration. The boundary conditions for the space charge density are derived from the direct ionisation criterion. This technique doesn't rely on the Kaptzov hypothesis and can be used for any shape of the discharge electrode. The proposed algorithm has been compared with two approximate ones. One uses the Kaptzov hypothesis that the electric field on the corona electrode surface remains constant, with the value derived from the ionisation criterion, assuming that the electric field is Laplacian. The other one mechanically applies the Peek formula for the cylindrical wire, after replacing the wire radius with the surface curvature radius at given point of the electrode. The differences between all three approaches are negligible for small corona currents; they are noticeable, but still small, for higher currents.

Cytochrome P450 3A4-catalyzed Testosterone 6β-Hydroxylation Stereochemistry, Kinetic Deuterium Isotope Effects, and Rate-limiting Steps

Testosterone 6beta-hydroxylation is a prototypic reaction of cytochrome P450 (P450) 3A4, the major human P450. Biomimetic reactions produced a variety of testosterone oxidation products with 6beta-hydroxylation being only a minor reaction, indicating that P450 3A4 has considerable control over the course of steroid hydroxylation because 6beta-hydroxylation is not dominant in a thermodynamically controlled oxidation of the substrate. Several isotopically labeled testosterone substrates were prepared and used to probe the catalytic mechanism of P450 3A4: (i) 2,2,4,6,6-(2)H(5); (ii) 6,6-(2)H(2); (iii) 6alpha-(2)H; (iv) 6beta-(2)H; and (v) 6beta-(3)H testosterone. Only the 6beta-hydrogen was removed by P450 3A4 and not the 6alpha, indicating that P450 3A4 abstracts hydrogen and rebounds oxygen only at the beta face. Analysis of the rates of hydroxylation of 6beta-(1)H-, 6beta-(2)H-, and 6beta-(3)H-labeled testosterone and application of the Northrop method yielded an apparent intrinsic kinetic deuterium isotope effect ((D)k) of 15. The deuterium isotope effects on k(cat) and k(cat)/K(m) in non-competitive reactions were only 2-3. Some "switching" to other hydroxylations occurred because of 6beta-(2)H substitution. The high (D)k value is consistent with an initial hydrogen atom abstraction reaction. Attenuation of the high (D)k in the non-competitive experiments implies that C-H bond breaking is not a dominant rate-limiting step. Considerable attenuation of a high (D)k value was also seen with a slower P450 3A4 reaction, the O-dealkylation of 7-benzyloxyquinoline. Thus P450 3A4 is an enzyme with regioselective flexibility but also considerable regioselectivity and stereoselectivity in product formation, not necessarily dominated by the ease of C-H bond breaking.

Forced corona method for the evaluation of fabrics with conductive fibres

Modern fabrics for protective clothing, used in environment where the level of static charge must be controlled, are composites where a grid or stripes of conductive fibres are present inside a matrix of highly resistive base fabric. In protective clothing, where the conductive fabric elements are not effectively grounded, corona discharge is the major limiting mechanism for fabric charging. In this paper, corona discharge of electrostatic discharge protective fabrics has been studied. A new experimental method, forced corona, was developed for the measurement of corona onset and offset potentials as well as corona current. According to results, the residual level of fabric surface potential after corona discharge was the lowest in fabrics containing core conductive fibres. The behaviour is because of the small dimensions and sharp edges of the core conductive fibres.

Power losses in electrical networks depending on weather conditions

Specific power losses to corona and to leakage currents over overhead insulators are presented for 110 – 750-kV transmission lines with different phase design and pole types for different weather conditions. Consumption of electric energy for ice melting on conductors of various cross sections is evaluated. Meteorological data of 1372 weather stations in Russia are processed for a period of 10 years. The territory of the country is divided into 7 regions with approximately homogeneous weather conditions. Specific power losses to corona and leakage currents over overhead insulators are presented for every region.

Influence of Oxygen and Dissolved Inorganic Additives on the Removal of Gaseous Acetylaldehyde by Use of a Wetted‐Wall Corona Discharge Reactor

AbstractA cylindrical wetted‐wall corona discharge reactor was used for the removal of acetaldehyde in gas mixtures of N2 and O2. Gaseous acetaldehyde was removed from the gas stream by simultaneous absorption and gaseous corona reaction. The acetaldehyde absorbed in water, was decomposed by the aqueous radical, OH, produced by contact of the gas corona with the water film. There is an optimized oxygen concentration for the effective removal. When oxygen coexists in the gas mixture at 5 %, acetaldehyde was effectively removed, resulting in overall sustainable removal of acetaldehyde. However, an increase in oxygen concentration resulted in a decrease in the extent of removal, when the corona current was excessively high. This is due to corona‐induced turbulence broadening the residence time distribution of gas in the reaction zone. The decompositions of absorbed acetaldehyde and TOC in water were obviously affected by the varied oxygen concentrations. Acetaldehyde was not removed in the absence of oxygen. The dissolved inorganic additives, NaOH and HCl, strongly affected the acetaldehyde absorbability into water and subsequently, the decomposition rate of the absorbed acetaldehyde.

An empirical formula for negative corona discharge current in point-grid electrode geometry

A series of measurements carried out with a point-grid electrode system has clarified that the current-voltage characteristics of the negative corona discharge obey the Townsend relation, further, in which the coefficient is proportional to temperature and the power of the electrode gap independently, and the corona onset voltage is proportional to the product of the reciprocal of temperature and the power of the electrode gap. The empirical formula derived from their relations has estimated negative corona currents with an accuracy of 1μA for a given parameter set, which will allow application to ion generator design.