Pre-breakdown currents in insulating liquids stressed with non-uniform DC electric field

This paper is aimed at investigation of the pre-breakdown conduction characteristics of insulating liquids. Two mineral oils and a synthetic ester fluid were used in the tests. The current-voltage characteristics have been measured in the point-plane electrode configuration, the needle electrode was stressed with positive and negative DC voltage. The current voltage characteristics demonstrated non-linear behavior over a large range of voltages, this current behavior could be attributed to the space-charge saturation regime of conduction in insulating liquids. DC breakdown voltages have been monitored and registered. It has been shown that MIDEL 7131 synthetic ester has a lower breakdown strength as compared with the tested mineral oils. Also it has been shown that positive breakdown voltage is lower than the negative breakdown voltage for the insulating liquids used in this study.