Influence of the humidity and the relative air density in impulse breakdown tracks

The influence of the absolute humidity (H) and the relative air density (δ) in the trajectories of standard lightning impulse point-plane air gap breakdowns were investigated. For negative impulses the minimum radial distances (impact points on the plane) are slightly increased if the humidity is augmented, the maximum radial distances are decreased if the humidity is risen. For positive impulses there is no influence of H in both maximum and minimum distances. If δ decreased in general the impact points on the plane are more far away from the axis for negative polarity, if the gap distances are enlarged the influence of δ is greater. For positive impulses the effect of δ is not significant. This behavior is because H and oxygen (O₂) produce an inhibition in streamer propagation both in axial advance and in branching due to photon absorption