A novel fabrication technique of permittivity graded materials by flexible mixture casting method for GIS spacers

Summary

For the relaxation and optimization of electric field distribution around GIS spacers, the application of functionally graded materials (FGM) with spatial distribution of dielectric permittivity (e) can be one of the effective solutions. We have so far fabricated e- FGM by the centrifugal force method and verified the fundamental electric field relaxation effect around GIS spacers with e-FGM. However, the centrifugal force method may be hard to be applied to the actual GIS spacers with the larger size as well as by the possible drawbacks in mechanical and/or thermal properties due to the localized distribution of filler particles in e-FGM. In this paper, we propose the flexible mixture casting method as a novel and practical technique to fabricate e-FGM for GIS spacers. The flexible mixture casting method is to fabricate e-FGM by mixing epoxy composites with different permittivities in a casting mold, where the mixing ratio is continuously controlled. Each epoxy composite is expected to have different permittivity and similar particle diameter distributions, which can enhance the mechanical and/or thermal properties. We used different filler particles to be mixed in epoxy resin, i.e. SrTiO3 with the relative permittivity (er) of 332 and the mean diameter (?) of 10 µm and SiO2 with er = 3.7 and ? = 8.3 µm. We obtained er = 4 - 30 for the mixture of SrTiO3 and SiO2 in epoxy resin as a function of mixing ratio with keeping their total volume at 40 vol%, Based on this result, we evaluated the electric field relaxation effect around a GIS spacer with e- FGM by flexible mixture casting method. When a parabolic distribution of permittivity (er = 4 - 30) is supposed to be applied to e-FGM for a cone-type GIS spacer, the maximum electric field strength on the spacer surface is expected to be reduced by 19 % and the breakdown voltage can be improved by 26 % against the conventional GIS spacer with a constant permittivity (er = 4). The relaxation of the maximum electric field strength around the GIS spacer with e-FGM and the enhancement of breakdown voltage can be reflected to the downsizing of GIS spacer.

Additional informations

Keywords

GIS, Spacer, Functionally graded materials (FGM), Dielectric permittivity, Electric field grading