Boundary Conditions for the Positive Direct-Current Corona in a Coaxial System

The work shows the crucial need for a careful choice of boundary conditions, particularly near the corona electrode, and revises the boundary conditions usually employed in classical methods. Commonly adopted assumptions which result in the corona radius and corona voltage drop being taken as constant have been shown to be inappropriate, since they lead to ambiguity in the mobility values. Values of positive-ion mobility based upon all three measured parameters have been calculated, using various models for the corona region, and these show a decrease in mobility with increasing humidity. This mobility is consistent with the field equations, and no dependence was found upon field strength or ion aging. The models yield an estimate of the dimensions and voltage drop for the corona ionisation region and the value of the field at the corona electrod