The Corona Threshold for Coaxial Cylinders in Air at High Pressures

The approximate corona-starting relation for concentric cylinders Ec/δ = A + B/√rδ, long established at lower gas densities, has been checked in air to δ = 35 over the respective ranges of inner and outer cylinder diameters of 0.0178 to 0.635 cm and 4.72 to 15.40 cm (Ec = corona-starting field at surface of inner electrode; r = radius of inner electrode; δ = gas density relative to atmospheric; A, B = constants). The formula holds for both polarities as long as 1) the critical density beyond which spark-over occurs without antecedent corona is not exceeded and 2) a modified definition of corona starting is used for the negative discharge. Some peculiarities of high-δ corona are noted, including the marked effect of polarity on the reproducibility of Ec data and, under certain conditions, the appearance below Ec of a current of the same order of magnitude as normal corona current.