Simulation and Analysis of Corona Currents in Large Scale Coaxial Geometry due to Triangular Voltages

Abstract

Charged species can be generated in air due to corona discharges from sharp electrodes. They are of great concern in practical applications due to their ability to drift in the electric field and to accumulate on dielectric surfaces modifying electric field distributions. To understand better regularities of dynamic behavior of charge carriers produced by corona, series of experiments have been conducted at ABB Corporate Research Center in Västerås, Sweden. For this, a coaxial large scale electrode arrangement was utilized. Corona discharges were initiated by applying triangular voltages that allowed for studying drift of ionic species under controlled conditions. The experimentally obtained data required physical interpretation and this was the main objective of the present MSc thesis work. In the thesis, a computer model of corona discharges in air is presented and its implementation in COMSOL Multiphysics is described. The developed model is utilized for simulations of corona discharges in the set-up used in the experiments. The computed current-voltage characteristics are compared with the experimental results. Influences of different model parameters, including the effect of boundary conditions, on corona characteristics are studied and a set of parameters providing the best fit between experiments and simulations is identified. An analysis of physical processes in corona discharges in air under triangular voltages at frequencies 1-50 Hz is presented focusing on interpretation of experimentally observed phenomena.