Search

The paper presents the results of a numerical simulation of the effects of N2 on the characteristics of Trichel pulses in SF6 at 0.4 MPa. The simulation was performed in a 2D axisymmetric geometry assuming a three species discharge model for the applied voltage on the discharge electrode to be −25 kV. Three drift-diffusion equations coupled with Poisson's equation are considered to determine the dynamic behavior of Trichel pulses and the temporal and spatial distributions of charged species. The reduced ionization coefficient, the reduced attachment coefficient, the electron mobility, and the electron diffusion coefficient of SF6/N2 mixtures are obtained by solving the two-term Boltzmann equations. The content of N2 varies from 20% to 80%. The distribution of three charged species and the reduced electric field at the discharge tip are presented at different instants of time to explain the formation mechanism of the Trichel pulses in SF6/N2 mixtures. The time-dependent current, the total number of electrons, the positive ions, and the negative ions as well as the reduced electric field at the discharge tip under different SF6/N2 mixtures are analyzed to investigate the sensitivities of these properties to the N2 content. [ABSTRACT FROM AUTHOR]

Diffusion coefficients play an important role in the description of the transport of metal vapours in gas mixtures. This paper is devoted to the calculation of four combined diffusion coefficients, namely, the combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient, and combined pressure diffusion coefficient in SF6-Cu mixtures at temperatures up to 30000 K. These four coefficients describe diffusion due to composition gradients, applied electric fields, temperature gradients, and pressure gradients, respectively. The influence of copper fluoride and sulfide species on the diffusion coefficients is shown to be negligible. The effect of copper proportion and gas pressures on these diffusion coefficients is investigated. It is shown that increasing the proportion of copper generally increases the magnitude of the four diffusion coefficients, except for copper mole fractions of 90% or more. It is further found that increasing the pressure reduces the magnitude of the coefficients, except for the combined temperature diffusion coefficient, and shifts the maximum of all four coefficients towards higher temperatures. The results presented in this paper can be applied to the simulation of high-voltage circuit breaker arcs. [ABSTRACT FROM AUTHOR]

The 2D finite-difference frequency-domain method combined with the surface-impedance boundary condition is applied for the analysis of dispersion characteristics of lossy metal waveguides. Six electromagnetic field components are involved in the final eigen equation. By solving the eigen equation, the method finds the propagation constants for a given frequency. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 158–161, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20238 [ABSTRACT FROM AUTHOR]

A new method for the interneedle-distance optimization of a multineedle-to-plane barrier discharge reactor is presented. As we know, there is gas breakdown when, in some regions between electrodes, the electric field is higher than the breakdown field; hence, the regionmay play a dominant role for the discharge, and the enhancement of its volume ratio in the reactor will allow an increase in discharge energy density. This can be achieved by structure optimization. With the finite-element method, the 3-D profiles of an electrostatic field in the reactor are acquired for a series of interneedle distances, thereby the one-to-one relationship between the volume ratio and interneedle distance is obtained. This allows the optimal interneedle distance for power input efficiency to be identified, as related to the maximal volume ratio. The optimal distance is between 7.2 and 8.4 mm in our simulation range, decreasing with the increase of operating voltages from 16 to 26 kV. The simulation results are experimentally validated by discharge energy measurement as well as the performance of SO2 removal from indoor air. This structure optimization method leads to a simple way to obtain the optimal interneedle distance for energy input efficiency and hence benefits commercial use. [ABSTRACT FROM AUTHOR]

This paper mainly contributes to the estimation of 2-D current-density distribution in a moving arc root. For this purpose, the multiple-split-cathode-with-different-slit-angle method is used to perform measurements of the linear current distribution of the arc root in seven different directions. On the basis of the measurement results, a large system of linear algebraic equations is treated with the algebraic-reconstruction-technique algorithm to obtain the 2-D current density. The calculation results indicate that the transverse profile of current density in a moving arc root can be characterized by a high-current core with two low-current hysteretic wings and that the maximum current density tends to the fore part of it. [ABSTRACT FROM AUTHOR]