Negative DC corona inception in coaxial cylinders under variable atmospheric conditions: A comparison with positive corona

Characteristics of negative DC corona threshold inception in the coaxial cylindrical electrode arrangement are investigated based on experimental data and computations on avalanche growth considering a field and atmospheric conditions dependent photoelectron emission coefficient. A transition region between glow and streamer regimes of inception of the self-sustained corona discharge could be identified on the basis of space charge field effects on avalanche growth. Approximate expressions are introduced for satisfactorily estimating the negative corona inception field strength as interactively affected by conductor radius and atmospheric conditions. Polarity effects on corona inception characteristics are elucidated. The establishment of the glow corona generally occurs up to larger conductors for negative than positive corona; the opposite may also apply depending on atmospheric conditions. The inception field strength as well as its dependence on atmospheric conditions differs only slightly between negative and positive streamer corona; a critical avalanche number per unit length of ~108cm-1is required for both negative and positive streamer formation.