Sparkover of rod gaps stressed with impulse voltages of nonstandard waveshapes

The effect of an oscillatory nonstandard waveshape on the sparkover in air of rod-plane and rod-rod gaps has been studied for impulse voltages of both polarities up to 500 kV and times to crest of 7¿42 ¿s. The sparkover voltage was found to be never more than 15% in excess of that required for double-exponential waves of corresponding values of Tcr and values of a were typically 2¿4%. With oscillatory nonstandard waveshapes, sparkover does not always occur on the first voltage crest but can occur as late as the fifth. Voltage measurement of crest values can be precisely determined by a sphere gap if the gap is adequately irradiated.