The Choice of Suitable Gap Forms for the Study of Corona Breakdown and the Field Along the Axis of a Hemispherically Capped Cylindrical Point-to-Plane Gap

Publisher Website
Google Scholar
Abstract
The various corona gap forms suitable for the convenient investigation of corona phenomena of both signs in the laboratory that are capable of yielding quantitative data involving the Townsend integral for the thresholds of the manifold phenomena are discussed. For laboratory study the most convenient form of gap is the hemispherically capped cylindrical point‐to‐plane system. Analysis of the potential fall along the axis in such gaps by means of electrolytic model studies indicates that the essential parameter is L/r, the ratio of gap length, L, from point surface to plane relative to the point radius, r. The model study potentials are, however, incapable of giving accurate values of the field strength. These fields must be obtained by computation. Laboratory studies of corona indicate the desirability of relatively large values of L/r. Practical considerations based on studies at atmospheric pressure indicate point radii r of 0.025 and 0.05 cm with a ratio L/r=160 to be those giving the greatest flexibility and most widely separated thresholds at convenient potentials. The use of such point systems to standardize data is recommended. On this basis the field along the axis for the hemispherically capped cylindrical point‐to‐plane gap as computed by E. E. Dodd is given and here applied to the calculation of the point‐to‐plane Townsend integral for pre‐onset burst pulse thresholds in air as observed by H. W. Bandel. The value is compared with the values obtained by W. N. English for confocal paraboloids where the fields are accurately known. The results are satisfactorily consistent. Discrepancies in the fixing of burst pulse thresholds by various observers are discussed.