scholarly journals Electrical Breakdown in Air and in SF6

1995 ◽  
Vol 48 (3) ◽  
pp. 453 ◽  
Author(s):  
R Morrow ◽  
JJ Lowke
Keyword(s):  
Electric Field ◽  
Electric Field Distribution ◽  
Electrical Breakdown ◽  
Negative Ions ◽  
Continuity Equations ◽  
Positive Ions ◽  
Positive Space Charge ◽  
Attachment Coefficient ◽  
Positive Space ◽  
Positive Point

A theory is presented for the development of streamers from a positive point in atmospheric air. The continuity equations for electrons, positive ions, and negative ions are solved simultaneously with Poisson's equation. For an applied voltage of 20 kV across a 20 mm gap, streamers are predicted to cross the gap in 26 ns, and the calculated streamer velocities are in fair agreement with experiment. When the gap is increased to 50 mm for the same voltage, the streamer is predicted not to reach the cathode. In this case an intense electric field front rapidly propagates about 35 mm into the gap in 200 ns. For a further 9�5 �s the streamer slowly moves into the gap, until the electric field at the head of the streamer collapses, and the streamer front stops moving. Finally, only positive space-charge remains; this moves away from the point, allowing the field near the point to recover, giving rise to a secondary discharge near the anode. The electric field distribution is shown to be quite different from that found previously for SF6; this is explained by the much lower attachment coefficient in air compared with that in SF6. These results show that streamers in air have a far greater range than streamers in SF6. This greater range cannot be explained by comparison of the values of E*, the electric field at which ionisation equals attachment.

The structure of the impulse corona in a rod/plane gap I. The positive corona

1970 ◽  
Vol 315 (1520) ◽  
pp. 1-25 ◽  
Keyword(s):  
Spatial Distribution ◽  
Electric Field ◽  
Space Charge ◽  
Negative Ions ◽  
Corona Discharges ◽  
Theoretical Derivation ◽  
Plane Electrode ◽  
Positive Space Charge ◽  
Positive Ion ◽  
Positive Space

The dissipation of space charge following the growth of impulse corona discharges in positive rod/earthed plane gaps has been measured with an electrostatic fluxmeter. A method is described to determine the spatial distribution and magnitude of the space charge together with the associated electric field. Initial positive ion densities of up to 100 μC m -3 have been found. The total positive space charge deposited in a 40 cm gap at 160 kV is 500 nC. Electrons emitted from the plane electrode as a result of corona channels crossing the gap are shown to be trapped in the discharge space as negative ions. The recovery of the gap over several seconds is largely due to ionic drift to the electrodes. A theoretical derivation of the rate of deionization agrees with observed values.

Numerical Simulation of Leakage Current on Conductive Insulator Surface

2019 ◽  
Vol 8 (4) ◽  
pp. 9487-9492
Keyword(s):  
Numerical Simulation ◽  
Electric Field ◽  
Leakage Current ◽  
Method Of Lines ◽  
Electron Attachment ◽  
Negative Ions ◽  
Conduction Current ◽  
Insulator Surface ◽  
Finite Difference Approximations ◽  
Positive Ions

The outdoor insulator is commonly exposed to environmental pollution. The presence of water like raindrops and dew on the contaminant surface can lead to surface degradation due to leakage current. However, the physical process of this phenomenon is not well understood. Hence, in this study we develop a mathematical model of leakage current on the outdoor insulator surface using the Nernst Planck theory which accounts for the charge transport between the electrodes (negative and positive electrode) and charge generation mechanism. Meanwhile the electric field obeys Poisson’s equation. Method of Lines technique is used to solve the model numerically in which it converts the PDE into a system of ODEs by Finite Difference Approximations. The numerical simulation compares reasonably well with the experimental conduction current. The findings from the simulation shows that the conduction current is affected by the electric field distribution and charge concentration. The rise of the conduction current is due to the distribution of positive ion while the dominancy of electron attachment with neutral molecule and recombination with positive ions has caused a significant reduction of electron and increment of negative ions.

Continuum Modeling of Charged Particle Transport: RF Breakdown and Discharges of SF6

1986 ◽  
Vol 68 ◽  
Author(s):  
Brian E. Thompson ◽  
Herbert H. Sawun ◽  
Aaron Owens
Keyword(s):  
Electric Fields ◽  
Electron Attachment ◽  
Negative Ions ◽  
Rate Coefficients ◽  
Rf Discharge ◽  
Continuity Equations ◽  
Positive Ions ◽  
Discharge Model ◽  
Rf Breakdown ◽  
Charged Particle Transport

AbstractContinuity equations for the concentration of electrons, positive ions, and negative ions were constructed and solved to predict rf breakdown voltages and the electrical properties of SF, discharges.These balances for the three types of charged species include terms for convection (electric field-driven fluxes), diffusion, and reactions (ionization, electron attachment, and negative-positive ion recombination).The mobilities, diffusivities, and reaction rate coefficients necessary for the rf discharge model are based on reported measurements and calculations of these parameters in dc electric fields.The electric fields developed in the rf discharge are calculated from Poisson's equation and applied voltage conditions.Predictions based on this model are compared with measured rf breakdown characteristics of SF6.

scholarly journals EMERGING TRENDS IN WALL-FREE HALL THRUSTERS DEVELOPMENT

2021 ◽  
pp. 111-116
Author(s):  
I.V. Litovko ◽  
V.Yu. Bazhenov ◽  
A.A. Goncharov ◽  
A.N. Dobrovolsky ◽  
I.V. Naiko
Keyword(s):  
Electric Field ◽  
Space Charge ◽  
Hybrid Model ◽  
Cathode Surface ◽  
Virtual Cathode ◽  
Hall Thrusters ◽  
Positive Space Charge ◽  
Emerging Trends ◽  
New Type ◽  
Positive Space

2D-hybrid model was created for the proposed new type accelerator with a virtual cathode which allows to avoid sputtering of the cathode surface and to preserve the dynamics of accelerated ions. In the framework of the model, it was shown that ions first form a positive space charge in the system center, and eventually, under an ac-tion of created own electric field, emerge from both ends of the system.

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

2021 ◽  
Author(s):  
Mian Xiao ◽  
Lipeng Liu ◽  
Hengxin He ◽  
Bin Luo ◽  
Junru Che ◽  
...  
Keyword(s):  
Fluid Model ◽  
Negative Ions ◽  
Kinetic Scheme ◽  
Drift Region ◽  
Positive Space Charge ◽  
Simulation Based ◽  
Detailed Simulation ◽  
Simulation Results ◽  
Positive Space ◽  
Peak Value

Abstract 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 5 species and 7 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﹣.

scholarly journals The effect of small traces of water vapour on the velocities of ions produced by Röntgen rays in air

1910 ◽  
Vol 84 (569) ◽  
pp. 173-181 ◽  
Keyword(s):  
Electric Field ◽  
Water Vapour ◽  
Lateral Diffusion ◽  
Negative Ions ◽  
Complete Removal ◽  
The Other ◽  
Electric Force ◽  
Dry Air ◽  
Positive Ions ◽  
Low Pressures

Some experiments by Prof. J. S. Townsend on the lateral diffusion of a narrow stream of ions moving in an electric field led to the conclusion that negative ions in perfectly dry air are much smaller than those in air containing a small quantity of moisture. It was consequently to be expected that the complete removal of water vapour would cause an increase in the velocity with which negative ions move under the influence of an electric field of force. At his suggestion the following investigation of the velocities of ions in air at low pressures was undertaken, and it was found that, while the complete removal of water vapour had only a small effect on the velocities of positive ions, yet the same cause increased the velocities of the negative ions by a factor varying between 2 and 30 for the range of pressures and electric forces used in the experiments. The method adopted was to let the ions travel between two gauzes under a known electric force for a time t and then to reverse the field. If v is the velocity of the ions and d is the distance between the gauzes, then ions starting from one gauze will reach the other if t ≮ d / v . If t is gradually decreased, it is possible to find, by means of an electrometer, when ions cease to reach the second gauze; when this happens v = d / t .

Theory of positive columns in electronegative gases

1980 ◽  
Vol 370 (1742) ◽  
pp. 375-387 ◽  
Keyword(s):  
Electron Attachment ◽  
Negative Ions ◽  
State Theory ◽  
Discharge Column ◽  
Electron Collisions ◽  
Charged Species ◽  
Continuity Equations ◽  
Positive Ions ◽  
Axial Concentration ◽  
Very High

A steady state theory of the positive column of a glow discharge in an electronegative gas is presented. Excitation and ionization are assumed to occur by single-electron collisions with neutral molecules. Both electron attachment and detachment are included in the continuity equations, the latter being due to long-lived excited neutral molecules taken to be uniformly distributed in the gas. Fluid-type momentum equations are used to describe the motion of positive and negative ions and of the electrons. By retaining Poisson’s equation throughout the treatment it is possible to impose physically realistic boundary conditions on all three charged species. It is found that the radial distribution of negative ions in the column is substantially different from that of the positive ions and the electrons. This is caused by the inwardly directed drift velocity of the negative ions, which confines them almost completely to the central region of the discharge column. Since the axial concentration of the negative ions relative to that of the electrons depends on the ratio of the coefficients of attachment to detachment, the concentration can reach very high values indeed when the rate of detachment is low.

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