Thermal characterization and diffusivity of two mono-component epoxies for transformer insulation

Abstract

The main aim of this study is the thermal characterization of an organic insulation. This insulation is a compound of two mono-component epoxy resins: Epoxylite® primer and Elmotherm® varnish. A mono-component epoxy resin usually needs a high temperature to cure; through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), non-isothermal curves are obtained, allowing the estimation of activation energies of curing and decomposition processes respectively. If Model Free Kinetic (MFK) is used from DSC curves, it is possible to simulate isothermal curves at different temperatures and times, plotting activation energy as a function of the conversion degree. The simulation from TGA curves can be used to estimate lifetime of the resins and compare them following the Toop method. DSC also allows measurement of thermal conductivity, the melting peak of metallic gallium being used for this measurement. Finally, water diffusion in resins is studied. Currently, the Materials Performance research group of UC3M is working on the European project named “Essial”, where this organic insulation is used to protect the windings and the whole transformer from the environment. The results obtained will be used to determinate the optimal operating range for this insulator, demonstrating that both epoxies are required to achieve the insulating performance of the transformer and long curing times are required for full curing of Epoxylite®.