Nonlinearity in Impulse Breakdown of Very Large Air Gaps

Optical and electrical measurements of positive impulse discharges, in a point-to-plane electrode configuration, have been performed for electrode spacings ranging from I to 7 meters. A comprehensive analysis of these results indicates that the breakdown mechanism above 5.2 million volts (MV) differs from the mechanism operating at voltages below this level. A new extrapolation method for breakdown voltages levels above the measurable range has been developed. This method permits the determination of positive impulse breakdown voltage for very large gap spacings up to 14 meters, well above the maximum capabilities of presently available voltage sources. This study provides essential data contributing to a feasibility study of future UHV overhead systems.