Influence of Water Content Level on Partial Discharge Inception Voltage for Capacitively Graded Oil-Paper Insulation

Capacitively graded oil-paper insulation is still the most widespread and typically used insulation type for high voltage instrument transformers and bushings. As such, it is highly susceptible to water content within the paper. All manufacturers have the tendency to reduce this content to lowest possible values. The purpose of this research is to show how different water content levels influence the insulation properties of such types of insulation, by measuring the partial discharge inception voltage levels and tanδ. A numerous AC voltage tests were carried out at different temperatures. The results show a clear influence of the initial water content and operating temperature of the apparatus to the partial discharge inception voltage.