Analysis of the influence of specific humidity on positive streamer predischarges considering h/δ greater than 15 g/m3

The humidity correction factors specified by IEC Publication 60-1 (1989) and IEEE Std.-4 (1995) for impulse voltages are restricted to 1≤h/δ<15. However, values of h/δ≥15 g/m³ in many regions of the world are present. The IEC-60 and the IEEE Std.-4 procedures are based on the macroscopic observation that the atmospheric correction factors are larger when the discharge is governed mainly by positive streamers; while they tend to be lower when leaders or negative streamers are present. A better atmospheric correction factor implies to study the influence of atmospheric parameters on each discharge mechanism of the breakdown process. In this paper for standard lightning impulse voltages an analysis of the influence of absolute humidity divided by relative air density (h/δ) greater than 15 g/m³ on the positive streamer predischarges is reported.