AC creeping discharges propagating over solid–gas interfaces
Résumé
This study is aimed at the characterisation of surface discharges propagating over different solid materials namely glass, bakelite and epoxy resin immersed in three gases and their mixtures (namely SF 6 , N 2 and CO 2 , SF 6 /N 2 and SF 6 /CO 2 ) under AC voltage (50 Hz) in a point-plane electrode system. It is shown that the stopping length of discharges ( L f ) increases linearly with the applied voltage and decreases when the gas pressure is increased. L f is longer in CO 2 and N 2 than in SF 6 [ L f (N 2 ) > L f (CO 2 ) > L f (SF 6 )]; and the increase of SF 6 content in the investigated mixtures leads to a significant decrease of L f . Also, for a given gas, L f is slightly longer with glass and bakelite than that with epoxy resin indicating that the higher the dielectric constant, the longer the discharge is. Thus, the density of the discharge branches and L f reduce when the thickness of insulators increases and/or their dielectric constant decreases. Such observations evidence the implication of capacitive charge effect and electric field in the development of creeping discharges.