Characteristics of charge accumulation on coated electrode in SF6 gas

The SF₆ gas insulation system has been improved by covering the electrode with a dielectric layer. To raise the reliability of this method, the authors evaluated the influence of charge accumulation of the coated electrode on the breakdown characteristics and directly measured the charge accumulation of the coated electrode. By measuring the breakdown voltage of the coated electrode with and without charge elimination, it became clear that charges on the coated electrode enlarge both the absolute value and the dispersion of the breakdown voltage. By measuring the surface potential, two results were obtained. First, when the electric field of the tip of the electrode exceeded the theoretical breakdown field of SF₆ gas, the coated electrode was charged with the opposite polarity of the applied voltage. Second, the amount of the surface potential of the coated electrode varied depending on the polarity of the applied voltage and whether breakdown had occurred or not.