Negative DC Flashover of PTFE and PE Insulators in Sf6

With the extensive application of high voltage power transformation and distribution apparatus such as GIS and GIL, the dielectric strength of interior supporting insulators become an important factor for equipments´ safe and stable operation. In this paper, the cone-plane electrode assembly has been built to simulate the electric field distribution of the coaxial cylindrical configuration in GIS/GIL. Key factors that affect PTFE and PE insulators´ flashover characteristics in SF₆ under DC voltage are investigated mainly from the view of the insulator´s surface roughness and metal particles. Results show that the surface dielectric strength of umbrella insulators with smooth surface is fine whether the insulator is made of PTFE or PE. Moreover, whatever the metal particle adhered to insulator surface is near high voltage conductor or grounded enclosure, flashover voltages of the insulator are the lowest under relatively high pressures (≥0.3MPa) if the metal particle is positively charged.