Streamer Propagation and Flashover Along Insulator Surface in a Uniform Field in Air: Influence of Humidity

Results are presented concerning the influence of humidity on streamer propagation and flashover along a PTFE cylindrical insulator in a uniform field in air. Experiments were carried out in a three electrode arrangement consisting of a parallel-plane gap (12 cm), stressed by negative DC voltage and a needle in the earthed anode. Positive streamers were initiated by applying a pulse voltage at the needle electrode and propagate along the insulator surface. Streamer properties investigated are the electric field required for stable streamer propagation and the propagation velocity with field values sustaining stable streamer propagation and also under "overfields". The electric field required for flashover and the corresponding time were measured. It is shown that the electric field required for stable streamer propagation and the associated velocity increase with increasing humidity, whilst under "overfields" high humidity causes streamers to decelerate. Time to breakdown tends to decrease while the required field to breakdown increases with increasing humidity