IEEE Transactions on Dielectrics and Electrical Insulation Vol. 21, No. 3; June 2014 1035 DOI 10.1109/TDEI.2014.004445 A Model for Determining the Unipolar Ionic Saturation Current in Parallel Wire-cylinder Electrodes during Corona Discharge Antonios X. Moronis, Nikolaos Simou Technological Educational Institute (TEI) of Athens Department of Energy Technology Engineering Aegaleo, 12210, Athens, Greece Konstantinos N. Kiousis Heriot-Watt University Institute of Mechanical, Process and Energy Engineering Edinburgh, EH14 4AS, Scotland, UK and Emmanouil D. Fylladitakis Brunel University London Department of Electronic & Computer Engineering Uxbridge, Middlesex, UB8 3PH, London, UK ABSTRACT This paper presents a model for the determination of the ionic unipolar corona saturation current in parallel wire-cylinder electrodes in the air, based on the geometrical characteristics of the electric field lines distributing in the space surrounding the electrodes, under high voltage dc application. The distribution of the lengths of the electric field lines connecting the electrodes is determined by finite element analysis. Then the acquired data are treated theoretically in order to calculate the total saturation unipolar corona current limit for the aforementioned electrode arrangement. Experimental investigation has shown that corona current is closely related to the unipolar saturation current limits derived from the proposed model. Index Terms – Corona, electrodes, discharges, air gaps, finite element methods. 1 INTRODUCTION THE phenomenon of corona discharge is being used in numerous electrostatic processes [1]. Application examples include propulsion methods [2, 3], surface cooling [4], pollution control [5], cooling augmentation [6], and even agricultural applications [7]. The phenomenon initiates when a sufficiently high voltage is applied to an electrode with a small curvature radius, usually a very thin wire, a blade or a point. The strong electric field developed by the stressed electrode ionizes some of the gas molecules, which move towards the collector electrode. This charged particle flow effect is the hallmark of corona discharge in gases [8]. Generally, corona discharge is characterized by two regions; a small region very close to the surface of the emitter electrode, the ionization region, and the drift region, where the ionized gas molecules are forced towards the collector electrode [9]. Although the complete mechanism behind the corona discharge becomes excessively complicated when the phenomena taking place inside the ionization region need to be taken into account [10, 11], the overall system can be dramatically simplified by neglecting the effects inside the ionization region, an approach generally suitable for the assessment of macroscopic parameters. Today, there are several applications in which wire-cylinder electrode configurations are being used, such as ozone generators [12] and aerodynamics [13], while they also might find future use in other applications as well, where other electrode configurations are already being used, such as electrostatic precipitators [14], fluid accelerators [15-17] and electrospraying [18, 19]. An experimentally verified mathematical model for determining the unipolar saturation current distribution over the cylinder’s surface and the corresponding total saturation current limit in a wire-cylinder electrode configuration is being presented in this paper. Positive coronas have only been examined due to the fact that they are more stable and efficient for typical applications involving wire-cylinder electrode arrangements, such as ionic wind generators [20] or electrostatic separators [21]. Manuscript received on 30 October 2013, in final form 21 February 2014, accepted 24 February 2014.