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Adaptive Numerical Simulation of Streamer Propagation in Atmospheric Air
... The simple systems always suggest a path for discharges and breakdowns along the shortest distance between electrodes coinciding with the geometrical symmetry axis that is seldom the case in real situations. In the paper, streamer development between the edges of two flat circular discs is analyzed following the approach reported in [1, 2]. ...
... Model parameters used in the present study are adopted from123 and are listed in Table1. Dependences of the reduced ionization α/N and attachment η/N coefficients on reduced electric field strength E/N, Td, are shown inFigure 1 (N stands for gas density, m -3 , for given pressure and temperature). ...
... The model equations were complemented with boundary and initial conditions following123 and were implemented in Comsol Multiphysics software. To insure positivity of the solution of the drift-diffusion equations (1)-(3), they were converted into a logarithmic form and were implemented using customized weak formulation stabilized by introducing a test function similar to streamline diffusion with shock capturing. ...
... Covered track of a positive ion during a quarter of a period over the frequency of the applied voltage in a homogeneous electric field from Equation(15). ...
Due to the increasing use of power electronic converters in electrical grids, high voltage insulation systems are stressed by medium frequency voltages. The breakdown voltage of air decreases with increasing frequency especially for inhomogeneous electric fields. Here, breakdown voltages for different homogeneous and inhomogeneous electric fields are measured. Finite element method plasma simulations of space charge generation and their influence on the electric field distribution before the breakdown are done to support the explanation of the decreasing breakdown voltage in the frequency range from 50 Hz up to 30 kHz.
... Hybrid models that combine some of these models are also used [16], as further detailed in [17]. In particular, hydrodynamic fluid models have been shown to offer the advantages of efficiency, accuracy, and comprehensiveness, and have most often been employed [18,19]. However, due to extensive calculations and complex external conditions, the research has been focused on short gap discharges, such as corona discharge, dielectric barrier discharge, and other fields. ...
A numerical model based on the finite element simulation software COMSOL was developed to investigate the secondary arc that can limit the success of single-phase auto-reclosure solutions to the single-phase-to-ground fault. Partial differential equations accounting for variation of densities of charge particles (electrons, positive and negative ions) were coupled with Poisson’s equation to consider the effects of space and surface charges on the electric field. An experiment platform was established to verify the numerical model. The brightness distribution of the experimental short-circuit arc was basically consistent with the predicted distribution of electron density, demonstrating that the simulation was effective. Furthermore, the model was used to assess the particle density distribution, electric field variation, and time dependence of ion reactions during the short-circuit discharge. Results showed that the ion concentration was higher than the initial level after the short-circuit discharge, which is an important reason for inducing the subsequent secondary arc. The intensity of the spatial electric field was obviously affected by the high-voltage electrode at the end regions, and the intermediate region was mainly affected by the particle reaction. The time correspondence between the detachment reaction and the ion source generated in the short-circuit discharge process was basically consistent, and the detachment reactions were mainly concentrated in the middle area and near the negative electrode. The research elucidates the relevant plasma process of the secondary arc and will contribute to the suppression of it.
... It is expected that charge accumulation process on the dielectric inhomogeneities would lead to local field enhancements and provide alternative potential paths for the streamer to propagate and, hence, for branching. The basic approach for the simulation of streamer discharges in air was adopted from the model [7], which was verified against experimental data provided in the literature. ...
Fully coupled self-consistent model of streamer branching is presented. The model incorporates inhomogeneities in gas media representing, e.g., large molecular clusters, micro dust particles, etc., which act as centers for localized space charge build-up. The results of the performed simulations show that charge accumulation at such centers leads to their electrostatic interactions with the streamer head and causes its splitting. Quantitative analysis of the dynamics of charge carriers densities, generated space charges and magnitudes of the electric fields associated with the branching process is presented.
The influence of a solid dielectric barrier on development of an electrical discharge in air between needle and plane electrodes is analyzed by means of computer simulations. The computational model describing formation and propagation of a streamer in atmospheric air and accounting for charge transport and trapping on barrier surfaces is presented. The results of the simulations performed for 5 cm air gap containing solid barrier (plate) inserted between the needle and plane electrodes are discussed focusing on discharge dynamics and associated electric fields.
Fluid models of gas discharges require the input of transport coefficients and rate coefficients that depend on the electron energy distribution function. Such coefficients are usually calculated from collision cross-section data by solving the electron Boltzmann equation (BE). In this paper we present a new user-friendly BE solver developed especially for this purpose, freely available under the name BOLSIG+, which is more general and easier to use than most other BE solvers available. The solver provides steady-state solutions of the BE for electrons in a uniform electric field, using the classical two-term expansion, and is able to account for different growth models, quasi-stationary and oscillating fields, electron–neutral collisions and electron–electron collisions. We show that for the approximations we use, the BE takes the form of a convection-diffusion continuity-equation with a non-local source term in energy space. To solve this equation we use an exponential scheme commonly used for convection-diffusion problems. The calculated electron transport coefficients and rate coefficients are defined so as to ensure maximum consistency with the fluid equations. We discuss how these coefficients are best used in fluid models and illustrate the influence of some essential parameters and approximations.
The propagation of streamer discharges in air in strongly divergent electric fields and their interaction with solid dielectric barrier inserted between the energized electrodes are analyzed by means of computer simulations. The model used is based on a hydrodynamic approximation of the transport of charge carriers in both media (electrons and ions in air, and electrons and holes in solid) coupled with Poisson's equation for the electric field and accounts for charge injection and accumulation on gas-solid interfaces. The model is solved numerically utilizing customized finite-element formulation employing streamline upwind Petrov-Galerking method for stabilizing solution of drift-diffusion equations for fluxes of charged species. The results of the simulations performed for conditions of earlier reported experimental studies are presented and discussed. It is shown that streamer discharges may develop in different modes depending upon particular conditions and are capable of propagating along solid surfaces in the direction transverse to the applied field. In the latter case, their progress is fully controlled by space and surface charges accumulated within discharge plasma and on gas-solid interfaces. The developed calculation method creates a base for considering more complicated and practically oriented tasks.
Pulsed-discharge development in a point-to-plane geometry is investigated with subnanosecond temporal resolution. A short high-voltage pulse with a duration of 400 ps and peak voltage U = 224 kV was applied to a discharge gap of 1-30 mm. The discharge propagated in atmospheric-pressure air. Ultrahigh overvoltage (5-50 times) generates runaway electrons in the front of ionization wave and increases the plasma channel diameter and velocity of ionization wave propagation. Formation of homogeneous atmospheric-pressure nonequilibrium plasma has been demonstrated.
Cross section data are collected and reviewed for electron collisions with oxygen molecules. Included are the cross sections for total and elastic scatterings, momentum transfer, excitations of rotational, vibrational, and electronic states, dissociation, ionization, electron attachment, and emission of radiations. For each process, the recommended values of the cross sections are presented, when possible. The literature has been surveyed through the end of 2007.
A study is made of the photoionization of N2-O2 mixtures by radiation
from an electric discharge burning in the same gas. The molecular bands
of nitrogen in the vacuum ultraviolet are shown to be the source of the
ionizing photons. It is established that photoelectrons arise in
response to the direct ionization of oxygen molecules, which also
determine the absorption of ionizing radiation. An analytic expression
for calculating the rate of photoionization is obtained that agrees
satisfactorily with the experimental data.
The discharge behaviour in short metallic-dielectric electrode gaps
in air at atmospheric pressure is examined as a function of the surface charge
density on a dielectric anode. The charge distribution is assumed to be
Gaussian and calculations are carried out using a two-dimensional model with
rotational symmetry. Discharge development shortly after discharge inception
(t = 0.1 ns) is compared to that in proximity to discharge quenching
(t = 1.0 ns). The results indicate that surface charge accumulation, as a consequence
of successive discharges of like polarity, appreciably influences the photon
flux at the cathode and the photoionization rate in the gas volume; it has a
marked effect not only on the discharge behaviour at the longer development
times but also shortly after discharge inception.
A theory is presented for the development of the first streamer when a positive voltage is abruptly applied to a point in air at atmospheric pressure. The continuity equations for electrons, positive ions and negative ions, including the effects of ionization, attachment, recombination, electron diffusion, and photoionization, are solved simultaneously with Poisson's equation. With an applied voltage of 20 kV across a 50 mm gap, the streamer does not reach the cathode. An intense electric field front propagates away from the point into the gap to a distance of 35 mm in 200 ns. During the next the streamer only moves a further 2 mm into the gap, and the electric field at the head of the streamer collapses. Finally, only positive space charge remains which moves away from the point, allowing the field near the point to recover after ; free electrons can thus give rise to a secondary discharge near the anode. The electric field distribution is shown to be quite different from that found previously for in that the electric field in the column of the streamer is generally only a fraction of the critical field for which ionization equals attachment. Streamers for a given applied voltage have a far greater range in air than in . The results presented for air also apply to flue gas mixtures, since the important material properties of both gases are very similar.
Cross section data have been compiled for electron collisions with nitrogen molecules, based on 104 references. Cross sections are collected and reviewed for: total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational, and electronic states, dissociation, ionization, and emission of radiation. For each process, the recom-mended values of the cross section are presented for use. The literature has been surveyed through the end of 2003. © 2006 American Institute of Physics.
Nonthermal plasmas have been widely used for various applications. Observation of a discharge plasma is an essential aspect for understanding the plasma physics of this growing field. In this paper, the propagation of a general pulsed discharge having a 100-ns pulse duration is observed by taking framing and streak images and spectroscopic measurement. The results showed that two discharge phases exist in the general pulsed discharge, namely, a streamer discharge and the following glowlike discharge. Between these two phases, the electrode gap impedance changed dramatically which could cause impedance mismatching between the power generator and the electrode. In addition, the gas temperature increased about 150 K during the glowlike discharge, which causes further energy loss in plasma-enhanced chemical reactions. Consequently, it was decided to remove the glowlike discharge phase and to only have the streamer discharge. A nanosecond pulsed power generator having a pulse duration of 5 ns was developed, and the observed discharge propagation ended before it shifts to the glowlike discharge. The streamer propagation velocity with the nanosecond pulsed discharge was 6.0-8.0 mm/ns, which is much faster than that of a general pulsed discharge, and showed little difference between positive and negative voltage polarities.
A numerical study has been carried out to understand the influences of barrier arrangements on the discharge characteristics of dielectric barrier discharge (DBD). A 1.5-dimensional (1.5-D) modeling is considered in the arrangements of bare, single-barrier, and double-barrier electrodes while a two-dimensional (2-D) approach is employed in a configuration of ferroelectric packed discharge (FPD). Numerical simulations show that the evolution of microdischarges in DBD occurs sequentially in the three distinctive phases of avalanche, streamer, and decay, and that the dielectric barriers make streamer discharges stabilized and sustained in lowered electric fields without transition to spark compared with no barrier case. Especially, the highly nonuniform strong electric field effect created by the pellets appears to be formed in FPD, which enables the flue gas cleaning to be expected to enhance the decomposition efficiency.