Threshold Inception Conditions for Positive DC Corona in the Coaxial Cylindrical Electrode Arrangement under Variable Atmospheric Conditions

The conditions for threshold inception of positive DC corona in the coaxial cylindrical electrode arrangement are investigated. The establishment of the self-sustained corona discharge in glow or streamer form, as influenced by conductor radius and atmospheric conditions, is evaluated through detailed computations that consider space charge field effects on avalanche growth. The salient corona characteristics at threshold inception are assessed and discussed through comparisons with literature experimental data. In a wide range of inner conductor radius and atmospheric conditions corona initiates in streamer form when a critical avalanche number per unit length of about 10(8) cm(-1) is attained. Accurate formulation of the critical field strength required to sustain ionization allowed for the derivation of approximate expressions accounting well for the interactive effects of conductor radius and atmospheric conditions on the corona inception field strength in both glow and streamer regimes.