Theory of electric corona including the role of plasma chemistry

Abstract

The traditional theory of corona is cast in terms of ionization and attachment coefficients and gives good quantitative predictions of the voltage for the onset of corona as a function of the diameter of the corona wires, temperature, pressure and characteristics of the gas. Furthermore, it gives a fair qualitative description of the corona discharge itself as a function of space and time. The motion of electrons, positive ions and negative ions formed by electron attachment, can produce distortions to the electric field by space charge effects which result in Trichel current pulses for negative voltages and “streamers” for positive voltages. Recently it has been realized that the medium of the corona discharge in air, for example, is not ordinary air, since the properties of the air are changed by the corona discharge itself. Of particular importance for properties of the corona discharge are the many excited states and metastable atoms and molecules that are created by the corona discharge, which may influence the electron density by detachment of negative ions or make possible two-step ionization. Rate constants of those reactions of plasma chemistry, which involve electrons in the discharge, are a function of the local electric field. In the present paper, mechanisms of plasma chemistry are proposed to explain the voltage for spark breakdown between corona wires. © 1994, Walter de Gruyter. All rights reserved.