Filling ratio control of TiO2 and SiO2 in epoxy composites for permittivity-graded insulator with low coefficient of thermal expansion

Abstract

The feasibility of a permittivity-graded epoxy insulator with a low coefficient of thermal expansion (CTE) was clarified by evaluating the dielectric and thermomechanical properties of TiO2/SiO2 epoxy composites, which were epoxy composites co-filled with TiO2 and SiO2 particles. Upon varying the filling ratio of TiO2 to SiO2 while keeping the total filler volume constant, the relative permittivity of the TiO2/SiO2 epoxy composites varied in the range of 3.5–7.5 in our experiment while the CTE remained similar to that of an aluminum conductor used in gas-insulated power apparatus. The range of the relative permittivity of the TiO2/SiO2 epoxy composites with a low CTE satisfied the condition for realizing a permittivity-graded epoxy insulator. The application of an appropriate gradient of the permittivity distribution to a permittivity-graded epoxy insulator with a low CTE resulted in the relaxation of the electric field on the surface of an insulator.