Surface charge decay on insulators in air and sulfurhexafluorid - Part I: Simulation

The decay of surface charges on polymeric insulators in air and SF(6) is studied. Surface charges decay by three mechanisms, by volume and surface resistivity of the insulator as well as by neutralization from the gas. These mechanisms are investigated. In particular the mechanism of gas neutralization is explained in detail. It is shown that within a certain volume ions generated by natural radiation lead to a neutralization of surface charges on specimens and can contribute significantly to surface charge decay. Relevant gas parameters like ion pair generation, ion mobility and ion-ion recombination coefficient are given for air and SF(6). The decay of surface charges generated by corona discharge is simulated by taking the three mechanisms into consideration. The intention of the simulation is to quantify the effect of the individual mechanisms of the decay of surface charges and to provide the patterns needed to interpret the experimental result given in part II of this study.