PhD Loriane DESMARS

“Study of electrical and thermal properties of epoxy-anhydride composite materials for high voltage insulation”

The integration of renewable energies to the power grid requires its modification in order to ensure its stability, security and efficiency. Improving ultra-high voltage alternative current (UHVAC) gas insulated substations (GIS), e.g. reducing their size or increasing their voltage, is one of the challenges induced by the development of the future power grid, the supergrid. Increasing the ability of solid insulators used in such equipment to withstand electro-thermal stress has been identified as the main obstacle to overcome. The work presented in this manuscript has been motivated by the necessity to develop more efficient electrical insulating materials compared to commercially available ones. An epoxy-anhydride matrix filled with micron sized alumina, often used to produce GIS solid insulators, has been used as a reference for this study. We decided to keep the matrix of the reference material throughout our work and to concentrate on the filler influence in order to optimize the properties of the composites. The impacts of the nature of the filler (alumina or hexagonal boron nitride), of its shape factor (platelets or almost spherical particles) and of its volume fraction upon thermal conductivity, coefficient of thermal expansion, dynamic mechanical properties, dielectric properties, high voltage direct current (DC) conductivity and AC breakdown strength have been highlighted. The experimental study of structure-property relationships is completed by dielectric properties and thermal conductivity modelling using the effective medium theory.

Key-words: epoxy-anhydride, high voltage insulation, hexagonal boron nitride, alumina, dielectric properties, breakdown strength, electrical conductivity, thermal conductivity, modelling, effective medium theory.

Thesis co-director: Sébastien Pruvost