State estimation of accelerated aged mineral filled epoxy insulating materials

Polymeric materials like mineral filled and fibre reinforced epoxy resins were applied in many power apparatus for electric insulation. Outdoor and indoor insulation systems in condition of high humidity, partial discharges (PD) and mechanical overstresses lead to lifetime reduction. Aims of this investigation is the extension of operating time due to economical reasons, reduction of maintenance and monitoring dielectric properties under environmental stress. Partial discharges are driven by a high local electrical field strength and prefer to propagate along local weak spots (treeing). The weakest spots are arranged at the interface (incomplete moistened areas, blisters, micro cracks) so that partial discharges and treeing appear in or near the interface. Similar to outdoor applications mineral filled epoxy test specimens are aged by water immersion. The loss factor, the electrical and mechanical properties are measured in selected time intervals. Test specimens are exposed to high electric stress of varied levels. In between PD activity is detected. The time until the breakdown occurs is determined (so-called lifetime). The loss factor measurement and partial discharge analysis can help to classify materials and give information about the aging state of the specimens