Influence of humidity on surface streamer propagation in a uniform field in air

Knowledge of surface streamer characteristics as influenced by the insulating surface and atmospheric conditions is important for the better understanding of the flashover mechanism, hence also for an efficient design of insulating systems under various environmental conditions. In the present study positive streamer propagation along PTFE and Nylon cylindrical insulating surfaces is investigated in a uniform field in air under variable absolute humidity. Streamers were initiated by applying at an auxiliary needle electrode, located at the earthed anode plane electrode, a pulse voltage variable in amplitude and propagated along an insulating surface towards the upper plane electrode, which was stressed by negative DC voltage. The electric fields required for threshold and stable surface streamer propagation and the velocity of stable streamer propagation, being higher than that for air alone and also slightly higher for PTFE than Nylon insulator, increase with absolute humidity. Empirical relationships have been derived, accurately expressing the effects of absolute humidity on surface streamer propagation field and velocity. Results are compared to that obtained in the case of streamer propagation in air alone based on previous work.