Dielectric properties of SF6/N2 gas mixtures on a full scale model of the gas-insulated busbar

Investigations of the dielectric properties of SF₆, N ₂ and mixtures have been carried out using a full scale model of a gas-insulated busbar (GIB). The breakdown characteristics under clean conditions are similar to those in a uniform field gas gap. The breakdown voltage is the maximum in SF₆ and the minimum in N ₂, and shows positive synergism in gas mixtures. The breakdown voltages were proportional to the SF₆ content raised to the power of 0.12-0.24. In gas mixture at 0.5 MPa, the peculiar breakdown characteristics under particle attached conditions were obtained. The characteristics are dependent on applied voltage waveform. Under power frequency voltage, dielectric strength of gas mixtures in a particular SF₆ concentration range is higher than that of pure SF₆. In gas mixtures, the partial discharges behavior should be related to the increase of breakdown voltage. Under negative lightning impulse voltage, an addition of small amounts of SF₆ to N₂ results in a decrease of breakdown voltage. The negative ion should play an important role on this behavior