Two-Dimenslonal Analysis of Electrical Breakdown in a Nonuniform Gap Between a Wire and a Plane

Electrical breakdown of a gap between a wire (modeled as a hyperboloid) and a plane has been investigated numerically by solving the two-dimensional form of the diffusion flux equations for the charged particle number densities and Poisson's equation for the self-consistent electric field. Electron impact ionization, thermal ionization, and three-body recombination have been considered as the charged particle production and loss mechanisms. The electrode surfaces are considered to be absorbing and the initial density of the particles is small, but nonzero, A gap length of 0.5 mm is investigated and the gas medium is air or argon at atmospheric pressure. The temporal development of the profiles of ion and electron number densities, potential and electric field, and current growth on both the electrodes are presented when the applied voltage is 1500 and 2500 V for both positive and negative wires. When the wire is negatively biased, the peaks in the radial distribution of both of the charged particle densities near the wire occur off the axis except during the very early part of the breakdown. With positive polarity, the electron density maximum always occurs on the discharge axis, while for ions it moves away from the axis, later in the transient, due to the reverse particle drift in the electric field from the negative polarity case, The discharge spreads farther out into the ambient (almost two times the gap length) when the wire is negatively biased than with positive polarity. The effect of charge separation on the externally applied electric field is significant at voltages 2500 V and higher. Ionization is greater in argon than in air for a fixed potential difference between the electrodes. Disciplines Engineering | Mechanical Engineering Comments Suggested Citation: Ramakrishna, K., Ira M. Cohen and Portonovo S. Ayyaswamy. (1989) Two-dimentional analysis of electrical breakdown in a nonuniform gap between a wire and a plane. Journal of Applied Physics. Vol. 65(41). Copyright (1989) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Journal of Physics and may be found at http://jap.aip.org/resource/ 1/japiau/v65/i1/p41_s1 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/meam_papers/181 Twowdimenslonal analysis of electrical breakdown in a nonuniform gap between a wire and a plane K. Ramakrishna,a) I. M. Cohen, and P. S. Ayyaswamy Department of Mechanical Engineering and Applied iWechanics, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6315 (Received 18 April 1988; accepted for publication 9 September 1988) Electrical breakdown of a gap between a wire (modeled as a hyperboloid) and a plane has been investigated numerically by solving the two-dimensional form of the diffusion flux equations for the charged particle number densities and Poisson's equation for the self-consistent electri.c field. Electron impact ionization, thermal ionization, and three-body recombination have been considered as the charged particle production and loss mechanisms. The electrode surfaces are considered to be absorbing and the initial density of the particles is sman, but nonzero, A gap length of 0.5 mm is investigated and the gas medium is air or argon at atmospheric pressure. The temporal development of the profiles of ion and electron number densities, potential and ~lectric field, and current growth on both the electrodes are presented when the applied voltage 18 1500 and 2500 V for both positive and negative wires. When the wire is negatively biased, the peaks in the radial distribution of both of the charged particle densities near the wire occur off the axis except during the very early part of the breakdown. With positive polarity, the electron density maximum always occurs on the discharge axis, while for ions it moves away from the axis, later in the transient, due to the reverse particle drift in the electric field from the negative polarity case, The discharge spreads farther out into the ambient (almost two times the gap length) when the wire is negatively biased than with positive polarity. The effect of charge separation on the externally applied electric field is significant at voltages 2500 V and higher. Ionization is greater in argon than in air for a fixed potential difference between the electrodes.