Determination or Corona Starting Voltages or Nonunirorm Fields in Air

Until recently spark-over and corona starting voltages could be predetermined satisfactorily only in cases where experimental curves or empirical formulas were available. The advent of the Townsend theory,¹ and later its modification, led to a general method in breakdown calculations, although these were not entirely successful until a more complete knowledge of the Townsend coefficients for air was obtained.^2-4 Based upon this knowledge and from published data Ver Planck⁵ developed a method especially applicable for calculating initial breakdown voltages for nonuniform fields which converge toward the cathode. Though still empirical the increased data enabled more accurate results to be obtained from this method. The purpose of this paper is to apply the theory to a case where the field is produced between a flat plate and an edge formed by two intersecting planes, verifying experimentally.