The effect of barrier material on AC breakdown voltages of a hybrid gas-solid insulation is investigated by examining the behavior of electrostatic potential on barrier surfaces. Breakdown characteristics of air-insulated gaps with barriers made of three different polymeric materials are experimentally investigated. Further

measurements of surface potential on the barriers are performed and the results are utilized to obtain surface charge dynamic characteristics for the three polymeric materials and extract their electric conductivities

charge carrier mobilities

and trap energy distributions. It is found that the material with the lowest initial surface potential and fastest decay rate exhibits the highest bulk conductivity and carriers' mobility

as well as the lowest trap energy level. These properties provide the highest increase in AC breakdown voltages compared with pure air. It is concluded that materials where the accumulation of charges in the bulk is inhibited and decay of surface charges is facilitated

allow for higher operating voltages of AC hybrid gas-solid insulation systems. The mechanism of the effect of barrier material on AC breakdown voltage is discussed.