The interpretation of the surface charge pattern of spacers in gas-insulated transmission lines (GIL) is a crucial and important research topic, which requires a comprehensive understanding of charge behaviors at physical interfaces. Here, we report a surface charging phenomenon of spacers in presence of metal particles inside the direct current (DC) GIL. The charging of spherical metal particle on the spacer surface appears as dotted discontinuously distributed charge spots which are due to the charge injection from the induced charge of the metal particle and gas ionization over the metal particle surface. Concentrically distributed bipolar charge patterns are seen to build up, which are due to the surface trapping of charges from gas ionization at the end tip of the acicular metal particle. The lateral type of ionization obeys the law of dielectric barrier discharge of the needle-plate electrode at an intense DC electric field, which may bring significant influence on the safety of the spacer. The study in this letter provides direct evidence demonstrating the surface charge patterns of spacers in the presence of metal particles, which serves as an important basis in the design of DC GIL.

In this letter, we report functions of surface roughening and fluorination on suppressing linear metal particle-induced spacer surface charge accumulation. An appropriate increase in spacer surface conductivity by short-term fluorination and roughening not only increases the metal particle lifting voltage, but also weakens the particle activation. The spacer surface charge shows reduced charge density in roughened spacer, while fluorination modification significantly suppresses the charge density on the spacer surface. For roughened and fluorinated samples, the decrease of surface charge density and the intrinsic lower electric field (due to an increase in conductivity) near the triple junction both contribute to a higher particle lifting voltage. The content in this letter provides an approach to effectively suppress the charge accumulation induced by linear metal particles.