Model Of Corona Discharge Research Articles

Computational Fluid Dynamic Modelling of Particle Charging and Collection in a Wire-to-Plate Type Single-Stage Electrostatic Precipitator

Electrostatic precipitators (ESPs) have been widely used to control particulate pollutants, which adversely affect human health. In this study, a computational fluid-dynamic model for turbulent flow, particle trajectory, and particle charging in ESPs is presented using a pre-developed corona discharge model (Kim et al., 2010), wherein electric field and space charge distributions in the plasma region are numerically calculated. The ESP under consideration is a wire-to-plate single-stage ESP, which consists of a series of discharge wires and two collecting plates. Two different kinds of particulates are considered in this study; fly ash and sucrose particles. Fly ash was selected because many ESPs have been utilized in coal-fired power plants to capture fly ash particles generated from combustion. Sucrose was selected to compare our numerical calculation results with experimental data found in literature. The electrical characteristics of the ESP, particle trajectories, particle charge numbers, and collection efficiencies under various operating conditions are demonstrated. For fly ash, the overall collection efficiencies based on particle mass are 61, 86, 95, and 99% at 45, 50, 55, and 60 kV, respectively, at a flow velocity of 1 m s–1.

FDTD simulation of back-flashover at the transmission-line tower struck by lightning considering ground-wire corona and operating voltages

In this paper, we simulated transient voltages across insulators and back-flashover at the transmission line tower struck by lightning in the presence of corona on the ground wires. The FDTD method and simplified (engineering) model of corona discharge were used. Three two-circuit 60-m high towers, separated by 400m, with two overhead ground wires, and six phase conductors (two three-phase circuits) were considered. Back-flashover was assumed to occur at the upper, middle, or lower phase. Operating voltages of phase conductors were modeled by using a voltage source inserted between each phase conductor and ground. It is observed that ground-wire corona serves to reduce voltage peaks and delay the occurrence of flashover. For the upper-phase back-flashover due to a positive 50-kA stroke, the peak voltages across the upper-, middle-, and lower-phase insulators are reduced by 11%, 12%, and 12% by the ground-wire corona, and for a negative 50-kA stroke they are reduced by 8%, 9%, and 9%. Influences of ground-wire corona on transient voltages were also studied for the back-flashover at the middle or lower phase. Presence of operating voltages can lead to either increase or decrease of the peak of transient voltage, with the change being less than 20%. To the best of our knowledge, this is the first FDTD simulation of back-flashover at a transmission-line tower considering both ground-wire corona and operating voltages.

Unipolar model of negative corona discharge: Comparison of calculated and experimental I–V characteristics for the sphere–plane electrode system

Substantial computational resources and time are needed for computer simulation of the corona discharge with allowance for the sheath processes. This circumstance necessitates a search for and development of simplified models in which the processes in the sheath of corona discharge are reduced to the boundary condition at the surface of active electrode. A unipolar model that takes into account only one type of carriers is considered, and the boundary condition on the discharge electrode describes the rate of variations in the electron-flux density from the sheath. The calculated I–V characteristics are compared with experimental data for interelectrode distances ranging from several millimeters to several centimeters to reveal the applicability of the model. The simulated and experimental results are in good agreement at interelectrode distances of greater than 1 cm.

Improvement of Corona Discharge Model and Its Application on Simulating Corona Discharge in the Presence of Wind

To evaluate the effect of wind on corona discharges occurring on the tip of a grounded rod during a negative charging process of thundercloud, a two-dimensional numerical model has been improved by considering the wind velocity as a driving force for the movement of the corona charges. It was found that not only wind speed but also wind direction have a significant effect on the distribution of corona charges, the local electric field around the rod, and the corona current. (1) Under the same wind speed, a larger horizontal wind can result in less accumulation of corona charges, a larger electric field, and a larger corona current. However, when the speed is less than 5 m s−1, the effect of wind direction on the corona current was weak. (2) Under the same wind direction, a larger wind speed can cause a larger corona current. However, when the horizontal wind component is smaller than the vertical, the larger wind speed would cause a smaller electric field. Thus, it is necessary to take the effects of the wind direction into consideration, rather than to consider its speed only, when studying the corona discharge and its effects on the upward leader.

Influence of humidity on the characteristics of positive corona discharge in air

Detailed positive corona discharge characteristics, such as the corona onset voltage, pulse amplitude, repetition frequency, average corona current, rise time, and half-wave time, are systematically studied under different air humidity with a single artificial defect electrode. The experimental results indicate that the pulse amplitude decreases with the increase of air humidity; meanwhile, the repetition frequency increases as the air humidity increases. This phenomenon is different from that of negative corona discharge. Therefore, to have an insight into the mechanism of humidity influence on positive corona discharge, a positive corona discharge model based on the continuity equations is utilized. The simulations present a dynamic development of positive corona discharge and, meanwhile, reveal the humidity influence on positive corona discharge.

A domain decomposition method for three species modeling of multi-electrode negative corona discharge – With applications to electrostatic precipitators

The negative corona discharge problem for multi-electrode geometries is modeled by a three species model. The equations are solved using domain decomposition, by recognizing that multiple species are only present in a small part of the domain, and hence only need to be incorporated locally in the model.The method is applied to an industrially relevant three wire electrostatic precipitator geometry. The calculated current density is in good agreement with experimental data. To further illustrate applications of the three species solution, it is used for coupled particle, fluid, and electrostatic simulations to analyze particle collection properties.

FDTD simulation of direct lightning strike to a phase conductor: Influence of corona on transient voltages at the tower

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analysis of transient voltages at the tower of a transmission line caused by direct lightning strikes to an upper phase conductor. In the simulations, three 40-m towers, separated by 300m, with one overhead ground wire and three phase conductors are employed. Corona is assumed to occur only on the upper phase conductor struck by lightning. The progression of corona streamers from the conductor is represented as the radial expansion of cylindrical conducting region around the conductor. The reduction of transient-voltage peak due to corona is not very significant, so that the voltage at the nearest tower exceeds the insulation level of 66/77kV power line considered in this paper. For a 10-kA peak current, the upper-phase-conductor voltage peaks are reduced by 26% and 21% for a positive stroke with 1-μs- and 3-μs-risetime currents, respectively, and those for negative-stroke case are reduced by 18% and 13%, respectively. For a 20-kA peak current, the corresponding upper-phase-voltage peaks are reduced by 32% and 25% for the positive-stroke case, and those for the negative-stroke case are reduced by 22% and 15%.

A finite volume method for electrostatic three species negative corona discharge simulations with application to externally charged powder bells

A three species model for steady-state negative corona discharge is studied. Ionization, attachment, and recombination reactions are modeled. A novel unstructured finite volume algorithm to solve the equations is presented, using the secondary emission of electrons from the cathode to set boundary values for the electrons. To show the usefulness of the method for industrial applications it is used to characterize the electrostatic properties of an externally charged rotary powder bell used in the automotive industry. Experimental current density profiles are reconstructed with good accuracy, which validates the model and the method with real experimental data. • Numerical modeling of three species corona discharge in air and oxygen in wire-cylinder and needle-plane geometries. • Current density measurements of corona discharge with distances and voltages used for industrial spray painting applications. • Current density profiles of externally charged powder bells matched with simulations. • Finite volume algorithm in cylindrical coordinates using higher order convective schemes. • Validation of numerical algorithm for corona discharge model with one and three species.

FDTD Simulations of Corona Effect on Lightning-Induced Voltages

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to analysis of lightning-induced voltages at different points along a 5-mm radius, 1-km long single overhead wire taking into account corona space charge around the wire. Both perfectly conducting and lossy ground cases were considered. FDTD computations were performed using a 3-D nonuniform grid. The progression of corona streamers from the wire is represented as the radial expansion of cylindrical weakly conducting (40 μS/m) region around the wire. The magnitudes of FDTD-computed lightning-induced voltages in the presence of corona discharge are larger than those computed without considering corona. The observed trend is in agreement with that reported by Nucci et al. and by Dragan et al ., although the increase predicted by our full-wave model (up to 5% and 9% for negative and positive lightning return strokes, respectively) is less significant than in their studies (up to a factor of 2) based on the distributed-circuit model with sources specified using the electromagnetic field theory. The disparity is likely to be related to the use of different charge-voltage diagrams, explicitly assumed by Nucci et al. and Dragan et al . and resulting from our FDTD model with corona in the present study. When corona is considered, there is a tendency for induced-voltage rise time to increase. It appears that the distributed impedance discontinuity, associated with the corona development on the wire, is the primary reason for higher induced-voltage peaks and longer voltage rise times, compared to the case without corona.

FDTD Simulation of Insulator Voltages at a Lightning-Struck Tower Considering Ground-Wire Corona

In this paper, a simplified model of corona discharge for the finite-difference time-domain (FDTD) computations has been applied to the analysis of transient voltages across insulators of a transmission line struck by lightning. In the simulation, three 60-m towers, separated by 200 m, with one overhead ground wire and three-phase conductors are employed. The progression of corona streamers from the ground wire is represented as the radial expansion of cylindrical conducting region around the wire. On the basis of the computed results, the effect of corona discharge at the ground wire on transient insulator voltages is examined. The insulator voltages are reduced by corona discharge on the ground wire. The reduction of insulator-voltage peak due to the ground-wire corona is not very significant: the upper-, middle-, and lower-phase-voltage peaks are reduced by 15, 14, and 13% for a positive stroke with 50-kA-peak and 3-μs-risetime current, and those for the negative stroke with the same current waveform parameters are reduced by 10, 9, and 8%, respectively.

Modeling of corona discharge combined with Mn2+ catalysis for the removal of SO2 from simulated flue gas

This study investigated a mass-transfer process of the removal of SO2 from simulated flue gas by corona discharge combined with Mn2+ catalysis in wet reactor, including gas migration, liquid phase diffusion, and chemical reaction. The novelty formula of desulphurization efficiency and the flow rate of flue gas, discharge voltage, reaction enhancement factor, and the flow rate of water were established. It is reported that desulphurization efficiency remarkably increased with the increasing of enhancement factor and discharge voltage at 4000mgm−3 of SO2 and 0.05m3s−1 of gas flow rate. However, the desulphurization efficiency had a slightly increase with the increasing of water flow rate. It is realizable that the energy consumption could be reduced to be lower than 0.3kJm−3, which was acceptable for industrial application. The experimental data were well in accord with the calculated results of theoretical model.

FDTD Simulation of Lightning Surges on Overhead Wires in the Presence of Corona Discharge

A simplified model of corona discharge for finite-difference time-domain (FDTD) computations has been applied to analyzing lightning surges propagating along overhead wires with corona discharge. The FDTD computations simulate the experiments of Inoue and Wagner . In Inoue's experiment, a 12.65-mm radius, 1.4-km-long overhead wire was employed, and in Wagner 's experiment, a 21- or 25-mm radius, 2.2-km-long overhead horizontal wire was employed. The critical electric field on the surface of the 12.65-mm-radius wire for corona initiation is set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 1.4, 2.4, or 2.9 MV/m, and those for 21- and 25-mm-radius wires are set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 2.2 and 2.1 MV/m, respectively. The critical background electric field for streamer propagation is set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cp</sub> = 0.5 MV/m for positive voltage application and E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cn</sub> = 1.5 MV/m for negative voltage application. The FDTD-computed waveforms (including wavefront distortion and attenuation at later times) of surge voltages at three different distances from the energized end of the wire agree reasonably well with the corresponding measured waveforms. Also, the FDTD-computed waveforms of surge voltages induced on a nearby parallel bundled conductor agree fairly well with the corresponding measured waveforms.

A Simplified Model of Corona Discharge on Overhead Wire for FDTD Computations

A simplified model of corona discharge on overhead wire has been proposed for propagating surge computations using the finite-difference time-domain method. The radial progression of corona streamers from the wire is represented as the radial expansion of cylindrical conducting region whose conductivity is several tens of microsiemens per meter. Two wire radii are considered: 5 and 2 mm, in order to simulate two experimental con- figurations by Noda. The critical electric field on the surface of a 5-mm radius wire for corona initiation is set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 1.8 or 2.9 MV/m. For a 2-mm radius wire, it is set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> = 2.2 MV/m. The critical background electric field necessary for streamer propagation is set to E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cp</sub> = 0.5 MV/m for positive voltage application, and E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cn</sub> = 1.5 MV/m for negative voltage application. The computed waveform of radial current (including both conduction and displacement currents) agrees well with the corresponding measured waveform. Also, the computed relation between the total charge (charge residing on the wire and emanated corona charge) and applied voltage (qV curve) agrees well with the corresponding measured one, except for relatively low applied voltages. Additionally, the increase of coupling between the energized wire and another one nearby due to corona discharge is well reproduced.

Model of corona discharge from a thin point in a space-charge-limited current regime

Exact self-similar solutions for the problem of electric field and charge density distribution in the external region of a unipolar corona discharge from a thin point emitter have been found. The obtained solutions are valid outside the framework of the traditional Deutsch approximation based on the small influence of a volume charge on the shape of equipotential surfaces. The value of a saturated discharge current is estimated assuming that the corona discharge is generated by a certain part of the point.

Analysis of Corona Onset Electric Field Considering the Effect of Space Charges

A modified method based on the optimized charge simulation method (CSM) is used to predict the corona onset voltage and electric field when the space charges due to the corona are considered. Based on the streamer model of corona discharge, space charges generated near the conductors are predicted. In order to calculate the electric field at the conductor surface, space charges are replaced by some equivalent line charges near the conductor. Because of the existence of space charges, the corona onset electric field is changed a little. After a simplified model of actual power transmission lines is introduced with the help of rough coefficient, the corona onset voltage and corona onset electric field are calculated for different types of conductors finally.

Corona Discharge Model for Transmission Lines by Lumped Elements

This paper shows the insertion of corona effect in a transmission line model based on lumped elements. The development is performed considering a frequency-dependent line representation by cascade of π sections and state equations. Hence, the detailed profile of currents and voltages along the line, described from a non-homogeneous system of differential equations, can be obtained directly in time domain applying numerical or analytic solution integration methods. The corona discharge model is also based on lumped elements and is implemented from the well-know Skilling-Umoto Model.

Effects of air pressure and humidity on the corona onset voltage of bundle conductors

On the condition of adjusting air pressure from 58.7 to 98.7 kPa and air humidity from 5 to 17.3 g/m3 in the multifunctional artificial chamber, experiments on AC corona performance of scaled models of three kinds of bundle conductors are conducted and the mathematical model of corona discharge is proposed to calculate the corona onset voltages. Results indicate that the corona onset voltage of bundle conductors will decrease obviously with the decrease of air pressure, but the effect of air pressure on the corona onset voltage will decline with the increase of absolute humidity. When absolute humidity rises from 5 to 15 g/m3, the corona onset voltage increases slowly. Furthermore, the lower air pressure is, the more obvious effect of absolute humidity on the corona onset voltage is. Yet, the corona onset voltage drops remarkably when absolute humidity reaches 17.3 g/m3, owing to the condensation, which distorts the surface electric field, on the surface of conductors under high-humidity condition. In light of the condensation effect, the mathematical model of corona discharge is improved, which helps yield agreement between the measured results and the calculated results. Moreover, formulas for predicting corona onset voltages under various bundle configurations, air pressure and air humidity are also obtained. Calculated results from these formulas along with from mathematical models are compared with the measured results.

Modeling and characterization of field-enhanced corona discharge in ozone-generator diode

Electric field enhanced corona plasma discharge in ozone generator diode of axial symmetry has been investigated and characterized in theory. The cathode K of diode is made of a large number of sharpened nozzles arranged on various radial planes on the axial mast and pervaded in oxygen gas inside the anode cup A, produces high fields over MV/m and aids in the formation of a corona plume of dense ozone cloud over the cathode surface. An r-z finite difference scheme has been devised and employed to numerically determine the potential and electric field distributions inside the diode. The analyses of cathode emissions revealed a field emission domain conformed to modified Child-Langmuir diode-current. Passage of higher currents (over μA) in shorter A-K gaps d gave rise to cathode heated plasma extending from the corona to Saha regimes depending on local temperature. Plasma densities of order 102-106 m-3 are predicted in these. For larger d however, currents are smaller and heating negligible and a negative corona favoring ozone formation is attained. High ozone yields about 20 per cent of oxygen input is predicted in this domain. The generator so developed will be applied to various important applications such as, purification of ambient air /drinking water, ozone therapy, and so on.

Implementation of Fuchs' model of ion diffusion charging of nanoparticles considering the electron contribution in dc-corona chargers in high charge densities

A 1D corona discharge model coupled to a 2D-axisymmetric particle charging model are proposed in this paper to simulate nanoparticle charging process within a wire-tube air corona discharge subjected to an applied positive or negative dc voltage. This 1D discharge model provides the distribution of the electric field, the air ion and free electron concentrations for the 2D charging model which in turn solves the spatial distributions of the various charged nanoparticles within the tube. This 2D charging model takes into account the effect of electrons, on the basis of Fuchs' law usually employed in the literature for modelling of ion diffusion nanoparticle charging. The current approach is valid when the concentration of nanoparticles is much lower than the concentration of ionic species in the gas. Numerical results show that the positive air ions can be assumed to be solely responsible for the charging process in a positive air corona charger, while both the negative air ions and electrons play an important role in the negative charging. At high negative charge intensities, the effect of the electrons becomes appreciable due to their high conduction velocity. In general, the numerical results obtained are in good agreement with the experimental data reported in the literature.

A multi-species DC stationary model for negative corona discharge in oxygen; point-plane configuration

This paper analyzes the steady-state model of negative corona discharge in pure oxygen at room temperature and under atmospheric pressure assuming the point-plane geometry. Three species of charge carriers: electrons, negative oxygen ions O 2 - and positive oxygen ions O 2 + ions, are assumed. Five different ionic reactions for the corona discharge are studied, including electron impact ionization, three-body attachment of electrons to oxygen molecules, three-body recombination of electrons and positive oxygen ions, three-body recombination of negative and positive oxygen ions, and two-body recombination of negative and positive oxygen ions. The simulation results show the electron, negative and positive oxygen ion densities along the axial direction, lines of equal charge density for these three species in the air gap, and electric field distribution along the axis of symmetry.