Suppression of gas pressure and tank diameter of dry air GIS by combination of FGM spacer and insulating coating conductor

The combination of relative permittivity (εr) functionally graded material (ε‐FGM) insulating spacer and insulated coating high-voltage (HV) conductor has been developed to enhance insulation performance of gas-insulated switchgear (GIS) and gas-insulated transmission line (GIL) utilizing dry air as an alternative to SF6 gas. Previous studies investigated the effects of insulation improvements based on limited data and literature. However, in this study, more detailed data were obtained and investigated. An epoxy coating with a thickness of approximately 100 μm was applied to the conductor surface, and in combination with ε-FGM spacers, the LI-FOV was measured under the same conditions. The results showed that the LI-FOV increased by 27% at 0.4 MPa-abs and up to 28% at 0.6 MPa-abs compared with those of a uniform spacer. Furthermore, the potential reduction in filling gas pressure achieved by applying ε-FGM technology and insulating coatings to HV conductors in conventional 245 kV class insulated busbar tank was estimated. It was found that, although the combination of uniform insulating spacers and bare HV conductors required a filling gas pressure of ≥1.25 MPa-abs to satisfy insulation requirements, the pressure was reduced to approximately 0.75 MPa-abs by combining ε-FGM technology with insulation-coated HV conductors. In addition, when the filling gas pressure was set to 0.6 MPa-abs, the busbar tank diameter must be increased by at least 1.93 times for uniform spacers and bare HV conductors. In contrast, by combining ε-FGM spacers and insulation-coated HV conductors, the increase in busbar tank diameter could be reduced to 1.23 times. This methodology addresses the issue of increased filling gas pressure and insulation gap when dry air is used. This prevents excessive equipment enlargement and is expected to reduce energy consumption and CO2 emissions during manufacturing.