Free particle-initiated 60 Hz breakdown at a spacer surface in a gas-insulated bus

The influence of freely moving wire particles on 60-Hz AC surface flashover of epoxy and acrylic disk spacers in a 76/250 mm coaxial system was examined in sulfur hexafluoride gas at pressures of 300 and 500 kPa. The experimental results show that 0.45-mm-diameter aluminium wire particles, 6.4 mm long, will lift and reach a nearby spacer at voltages comparable to system operating voltage. The combination of metallic particles and spacer does not reduce the breakdown voltage below that for free particles without a spacer unless a particle is lodged on the spacer very close (<2 mm) to the center conduction. The probability of this occurring is much greater for horizontal disk or conical spacers than for vertically mounted disk spacers. The results are of interest in connection with the operation of GITL/GIS (gas-insulated transmission line/gas-insulated substation and switchgear) systems