On wire-to-plane positive corona discharge

Abstract

An experimental study of positive corona discharge in air for wire-to-plane geometry is presented for small gaps (from 8 to 16 mm). The measurements carried out show that wire-to-plane positive corona behaviour deviates from the Townsend relation in the low-current limit near the onset. This deviation is attributed to non-uniformity of the wire diameter and the roughness of the surface of the wire. We have introduced a correction to the Townsend relation based on a model of progressive onset potentials: the necessity of this correction is shown by means of an error analysis of the experimental data. The prefactors K1+ obtained are of the same order of magnitude as those achieved for other reported geometries. Transverse current density distributions have also been measured and the experimental data compared with the Warburg law. A simple analytic model of the discharge is derived: the discharge is modelled by considering the drift of ions from the coronating wire electrode to the grounded plane as a succession of non-interacting cylinders of charge. The space charge deposited by the cylinders on their arrival at the plane gives a current distribution that fits well with the experimental data.