The combined effect of partial discharges and temperature on void surfaces

Voltage stress, thermal stress and time of pd-exposure are parameters that influence the deterioration of void surfaces. A qualitative comparison of the degradation caused by these parameters has been made by accelerated ageing tests using different temperatures and voltages. The electrode system applied in the tests contained a flat cylindrical void with epoxy on one side and a stainless steel electrode on the other side. The surface degradation was examined by light-microscope and scanning electron microscope (SEM). The intention of the study was to look for characteristic features of the surface degradation, primarily of the epoxy, at the different ageing levels. Comparison of the aged void surfaces was performed at different ageing times. The results show that the deterioration patterns of the epoxy surface obtained at different ageing temperatures are clearly distinguishable. Typically, the deterioration pattern at room temperature was diffuse, while at 50/spl deg/C the surface exhibited a variegated and distinct pattern. The deterioration was hardly visible in case of 80/spl deg/C, the glass transition temperature of the epoxy specimen. The results add knowledge to the different modes of pd-erosion resulting from synergy with temperature.