A new correlation of sphere-gap data

The similarity principle for electrical discharges is used to correlate the most recent AIEE sphere-gap data for both positive and negative impulses. Empirical formulas are developed from which the entire range of data can be calculated to within about 1.5 per cent. Some practical results of this study are: 1. Spark-over curves for each value of spacing to diameter ratio are straight lines when plotted to logarithmic scales, at least to within the certainty of the present data. 2. A spark-over voltage chart covering the entire useful range of sphere sizes, spacings, and air densities can be constructed easily. 3. New air-density correction factors are derived which differ appreciably from those previously published.