Electrical and mechanical strength of mineral filled epoxy insulators in correlation to power loss factor

Polymeric materials like mineral filled and fibre reinforced epoxy resins are used in many power apparatus for electric insulation. Compared to ceramic and glass the composite insulators based on mineral filled polymers have many advantages. Epoxies offer new possibilities in developing electric insulations, especially to reach more compact design in electric power equipment. Due to their good adaptability, their convenient manufacturing technology, their very good electric and mechanical properties, mineral filled epoxies are the preferred duromeric materials for many high quality insulating systems. These materials for outdoor and indoor use show ageing phenomena under environmental stress which is not exactly known up to now. For this reason it is important to get a reliable state of estimation with loss factor and partial discharge measurement. Mineral filled epoxy test specimens are aged by water immersion due to environmental stresses in outdoor applications. The loss factor, partial discharges (PD), the glass transition temperature, the electrical strength and mechanical properties are measured in selected time intervals. The measuring results and a theoretical explanation of ageing effects on electric and dielectric parameters are presented.