Functionally graded materials (FGM) have spatial distribution of a material property in order to achieve efficient stress control. An application of the FGM to a solid insulator (spacer) for a gaseous insulation system, like gas insulated switchgear, is expected to improve electric field (Efield) distribution around the spacer.In this paper, we describe the applicability of the FGM spacer to gas insulated power equipment. In the FGM spacer, we gave spatial distribution of dielectric permittivity to control the E-field distribution inside and outside the spacer. This paper includes following key results for the applications of the FGM. Firstly, E-field simulation results when applying the FGM by a finite element method are presented, in which we show the effective reduction of the maximum field strength by applying the FGM. Next, a fabrication technique of the FGM spacer sample with not only step-by-step but also continuous changes of permittivity is presented by use of centrifugal force. Finally, dielectric breakdown tests using FGM samples which are accurately controlled the spatial distribution of permittivity are carried out under lightning impulse voltage applications. The test result indicates the increase of breakdown voltage (BDV). From these results, we verified the applicability and the fabrication technique of FGM spacer for improvement of the dielectric strength in the gaseous insulation system.

We have proposed a new concept for solid insulation; an application of FGM (Functionally Graded Materials). By controlling the distribution of dielectric permittivity inside solid insulators, we can achieve the efficient field control with keeping simple configuration of solid insulators.In this paper, we described a computer-aided optimization technique for the FGM solid insulators. By controlling the filler particle concentration in the matrix, an optimized field distribution is obtained. From the calculation results, we confirmed that the proposed optimization method could obtain novel distributions of permittivity, which have the highest performance of the field control effect. Finally, we could confirm the significant effect of FGM application for gas / solid composite insulation system.

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