Temperature effects on partial discharges in the combined system of a solid-liquid dielectric during lightning impulse voltage

The experimental work presented in this paper shows that the level of partial discharges in a solid-liquid dielectric increases with temperature. Partial discharge implications in the “metal-dielectric-metal” system were investigated using 1.2/50 μs impulse voltages under environmental temperatures of 20°C and 40°C. Although the repeat rate of the partial discharges appears to be almost independent of temperature, the charge associated with these partial discharges shows a remarkable increase. Furthermore, the threshold electric field required for partial discharge initiation was found to be reduced significantly as the system´s temperature was increased. The commonly accepted model of Gemant and Philipoff incorporating pre-existing defects or irregularities of the molecular structure in the solid-liquid dielectric and voids in the volume of the solid dielectric has been used for the interpretation of the obtained results. The approach of the solid-liquid dielectric to the above experimental results may imply a conductivity increase of the system in the high field region due to enhanced electron avalanche mechanism