Interface influence on the high-field conduction phenomena of a thin dielectric liquid layer

We report experimental work on the ac conduction phenomena of a thin dielectric liquid (capacitor impregnant) layer at high-electric field for several interfacial situations. The features revealed by these experiments show a strong dependence of the liquid electric losses (at frequency 50 Hz) and according to that, the liquid is in contact with a metallic or a polymer interface. An attempt is made to comment these measurements in terms of the existing theories of ionic conduction in nonpolar liquids: it turns out that charge-carrier injection in the neighborhood of the interface is the dominant contribution of the high-field liquid conductivity. A theoretical evaluation based on a unipolar injection model is given in agreement with the experimental results obtained in the different configurations.