Computation of negative corona inception field strength in the coaxial cylindrical electrode arrangement under variable air density

Corona discharge has attracted much interest among researchers as it has a lot of applications in industry and a number of effects on power systems. In the coaxial cylindrical electrode arrangement in air, simulating many practical applications, corona inception depends on the electric field strength around the inner conductor and on atmospheric conditions. In the present study a computational method for the estimation of the negative corona inception field strength in the coaxial cylindrical electrode arrangement under variable air density is presented. The method is based on streamer theory, involves Hartmann´s expression for the effective ionization coefficient and considers the effect of the space charge field on avalanche growth. The computed negative corona inception field strength is in good agreement with literature experimental data for an avalanche number varying with the product of relative air density and inner conductor radius. Streamer formation occurs rather through a multi-avalanche process, assisted by subsidiary avalanches owing to secondary ionization processes at the cathode and in air. Peek´s empirical formula for estimating corona inception field strength in the coaxial cylindrical electrode arrangement in air agrees satisfactorily with literature experimental data referring to negative corona inception.