Characteristics and Mechanism of AC-DC composite partial discharge of aging oil-paper insulation under switching impulse voltage in extremely uneven electric field

In this paper, we demonstrate the influence of accumulative aging on partial discharge of oil-pressboard insulation. The impulse voltage platform and partial discharge detection platform are built in this paper. The U-N characteristic of oil paper insulation was measured and the aging voltage was 42kV. Then, the cumulative impulse voltage aging was performed for 0, 200, 400 and 600 times respectively, and the partial discharge characteristics were measured under the AC-DC composite voltage, and the phase distribution spectra of the average discharge capacity and discharge frequency were drawn. Combined with the partial discharge spectrum diagram and the surface state of the cardboard, it can be concluded that the degree of depression of oil-paper insulated cardboard at the tip is an important reason affecting the variation of the characteristic quantity of partial discharge. The electric field and charge distribution in the partial discharge of paperboard were analyzed by using the finite element simulation software, and the mechanism of the cumulative effect on the characteristic of partial discharge was explained.