Evolution of the streaming current generated by an oil flow through a pressboard-application to flow electrification in power transformers

In high power transformers, pressboard and oil are needed for electrical insulation. Added to that, the oil is using as a cooler fluid of the system. Furthermore, during this last decade, the phenomenon of flow electrification at the oil-pressboard interface region is suspected to be at the origin of several damages occurring in power transformers, as well in Europe, North America or Japan. Thus as these phenomena are strongly in correlation with the physico-chemical processes at the interface, the goal of this experimental study is to characterize the streaming current intensity in function of the electrochemical and morphological properties of the pressboard. For this, the streaming current and the mean space charge density generated by an oil flow through a non degraded pressboard and pressboards degraded by electrical discharges have been characterized. The results show that the electrochemical modifications of the oil-pressboard interface highly enhances the flow electrification of the oil.