Influence of PD Between Needle and Plate Electrodes on Oil-Pressboard Aging Under Combined AC–DC Voltage

The converter transformer is an important equipment in the bulk power and long-distance power transmission projects, and the oil-pressboard insulation at the rectifying valve side, which mainly deals with combined ac–dc voltage, requires more study of discharge and its influence to ensure equipment safety. In this research, an oil-pressboard insulated experimental platform with needle and plate electrodes, which is similar to the sharp defects of components, such as the corner ring and the gasket of converter transformer, is established, and the photographs of partial discharge (PD) are used to analyze the influence of PD under the above experimental conditions; then, the generation and evolution of various PDs and their by-products can be researched in detail, which can influence the electrical aging process of oil-pressboard insulation. Results indicate that the main by-products brought by PD are bubbles and paper fibers, which can affect the proportion and development of subsequent PDs. These results can provide experimental support to research the internal mechanism of the electrical aging phenomenon of converter transformer, especially at its rectifying valve side.