BREAKDOWN OF A THIN DIELECTRIC LIQUID LAYER

This work concerns measurements of electrical breakdown on thin (10 mum to 100 mum) liquid dielectric (capacitor impregnant) layers for different interfacial situations. For this purpose a new uniform field electrode arrangement which represents interfacial conditions close to those of the industrial practice has been developed. It has been investigated experimentally how the dielectric strength depends on various factors such as electrode area, gap spacing, nature of the interface in contact with the liquid, and temperature. The breakdown phenomena are shown to be related either to high-field conduction (i.e. boiling or electrohydrodynamic cavitation leading to the generation of a vapor bubble in the prebreakdown regime), or related to the presence of particles or to local field enhancements.