Fabrication and Flashover Characteristics of Permittivity and Conductivity Graded Materials ($\varepsilon/\sigma$-FGM) for DC-GIS Spacers

The progressive development of HVDC transmission system has urged us to develop a novel technique in supporting the performance of DC power apparatus. Functionally Graded Materials (FGM) are one of the techniques that allow us to control the electric field distribution within the DC insulation system. Our previous works have analytically revealed that FGM with spatial permittivity $\varepsilon$ and conductivity $\sigma$ distributions applied to a 320 kV DC-GIS spacer could reduce the maximum electric field under all DC operating conditions. In this paper, we fabricated a cone-type $\varepsilon/\sigma$ -FGM spacer for DC-GIS and experimentally verified its flashover voltage improvement effect.