Inverse analysis of optimum permittivity distribution for FGM spacer in consideration with multiple objective functions in gaseous insulation systems

For relaxation of electric field (E-field) stress around solid insulation spacer in HV-GIS (Gas Insulated Switchgears), we have proved the effectiveness of an application of functionally graded materials (FGM) with spatial distribution of permittivity (ε-FGM). For this purpose, we have proposed a technique for inverse analysis of the permittivity distribution in an ε-FGM spacer. The technique can provide us optimum permittivity distribution with the maximum E-field stress relaxation with less computation time. In this paper, we developed the new technique of the inverse analysis under the consideration of multiple objective functions on the insulation performances. In our study, we focus on three kinds of functions: (a) dielectric strength in SF₆ gas gap, (b) dielectric strength on the spacer surface, and (c) dielectric strength on the embedded electrode/epoxy spacer interface. Under the consideration of three objective functions, the optimum permittivity distribution in ε-FGM spacer are modified full-automatically. Through the application results to GIS spacer, we obtain the inverse analysis of optimum permittivity distribution by only 11 times of iterations. As a result, we obtained 25% improvement of insulation performance around ε-FGM spacer compared with the conventional spacer with uniform permittivity distribution.