Partial discharge characteristics for Needle-Paper Defect in Oil insulation under the pre-breakdown stage

摘要

Converter transformer is one of the core equipment of DC transmission. Its operation safety and reliability is the reliable guarantee for the normal operation of DC transmission system. The large dispersion and randomness of partial discharge in the defect of oil paper insulated needle-board under the AC/DC composite voltage, and the large number of bubbles in the pre-breakdown stage of insulation further increase the complexity of partial discharge characteristics. The paper investigates the partial discharge characteristics for Needle-Paper Defect in Oil insulation under the pre-breakdown stage, which is of great significance. The average discharge amplitude and the average number of periodic discharge generally decrease with the increase of the pressure time. However, the variation rules of each group are not the same, and can be roughly divided into two types: fluctuation type change and monotonic type change. The difference between the two types of pre-breakdown characteristics is mainly related to the accumulation of bubbles on the surface of the board during the discharge process. According to the equivalent time-frequency spectrum, most of the discharge is concentrated in the dome area with the development of pre-breakdown.