Impulse Flashover Characteristics of Cone-Type Insulating Spacer for GIS Fabrication Using Nano- micro Composites or Grading Functional Materials

To investigate the possibility of miniaturization of a cone-type insulating spacer of gas-insulated switchgear (GIS), flashover voltage (FOV) characteristic by standard lightning impulse voltage in the SF₆ gas were studied by fabricating mini-model spacers applying nano-micro composite (NMC) materials or ε functionally graded materials (ε-FGM). This paper reports the results of each examination. For NMC materials, epoxy resin filled with SiO₂ micro-filler (MC) was filled with 1 vol % of nanofiller (SiO₂, TiO₂, SrTiO₃, Al₂O₃) to fabricated a 1/4 size cone-type insulating spacer, and the FOV in the SF6 gas was measured. In the case of negative impulse voltage, the scale parameter (η) of the Weibull distribution of the FOV was the same as that of the MC, but the shape parameter (m) decreased in the NMC. On the other hand, the FOV under positive impulse voltage of NMC materials filled with nTiO₂ and nSrTiO₃ increased by 12 % and 20 %, respectively, compared to that of the MC (without nano-filler). For the ε-FGM, a similar 1/4 size cone-type insulating spacer was fabricated, and the FOV was measured. ε-FGMs with relative permittivities (ε_r) between 12 and 4 were designed and fabricated using SrTiO₃ (ε_r=332) and SiO₂ (ε_r=4) micro-fillers. At the same time, a model with a permittivity ε_r=4 (uniform) was fabricated using only SiO₂ microfillers for comparison. The FOV at 0.5 MPa-abs under a negative impulse voltage of ε-FGM spacer is higher than that of a uniform sample by approximately 23 %. Thus, both NMC and ε-FGM can improve the insulating properties of the cone-type insulating spacer.