Flashover characteristic along the insulator under DC voltage in SF₆ gas

In order to promote the flexibility about the selection of transmission corridor, DC gas insulated transmission line (GIL) can be utilized to substitute part of the overhead line or cable in special environment such as cross connections inside of substations or connections between new remote generation areas and the load centers. One of the predominant factors that greatly threaten the insulation level of GIL is the accumulation of surface charges along the supporting insulators under DC voltage. Consequently, the cone-plane electrode system was established to simulate the electric field distribution of the coaxial cylinder configuration in GIL. Various kinds of insulators that had different geometry and surface roughness were placed between electrodes for test. Moreover, software was used to analyze the electric field distribution along the insulators' surface under DC voltage. Key factors that affect the insulator's flashover characteristics in SF6 under DC voltage were investigated mainly from the view of insulator's material and geometry. Results show that the insulator's surface conductivity and charging time constant both have remarkable influence on the surface charge accumulation as well as the flashover along the insulators in DC GIL. The selection principle about the insulator's surface conductivity in DC GIL and point for attention in optimizing insulator's geometry are put forward.