Investigation of Free-Moving Particles under AC Electric Field in Different Insulating Gas Mixtures

Free-moving conductive particles may affect the dielectric reliability of gas-insulated systems, e.g., gas-insulated lines (GIL) or gas-insulated switchgear (GIS). This paper reports on investigations on the behavior of free-moving particles under AC electric field, using different insulating gas mixtures. Multiple particles were positioned inside a GIL test setup with each particle placed within the same distance to a particle trap. To ensure reproducible and realistic particle geometry, cuboid particles were used. In this paper, a width correction factor was empirically determined for a well-known formula from the literature, which is used to calculate the lifting field strength for cuboid particles. While increasing the applied voltage, the movement of the particles was observed with a camera and further evaluated using ultra-high frequency (UHF) partial discharge (PD) measurements. The UHF phase-resolved partial discharge (PRPD) patterns of steel and aluminum particles in SF6, as well as in different alternative insulating gas mixtures, are compared and discussed. To determine the effectiveness of particle traps for different gas mixtures, further parameters are evaluated, such as the duration of each particle's movement and the number of particles reaching the inner conductor.