Research on assessment method for main insulation state of converter transformer based on time‐frequency domain dielectric response

The converter transformer is an essential part of the DC transmission system. Compared with traditional oil-impregnated AC transformer, main insulation bears more complex electric field aging stress during long-term operation. influence proportion components in AC/DC composite on still unclear. Therefore, a combined test platform and thermal was built laboratory, accelerated tests oil-paper under different ratios were carried out. Through time-frequency domain dielectric response characteristics insulation, quantitative relationship between characteristic parameters proportional coefficient stages obtained. results show that component pressboard prominent. maximum relaxation polarization time exponential polarization–depolarization current (PDC) can effectively characterize insulation. Meanwhile, to accurately assess state this paper established equivalent model for structure. A assessment method moisture content based proposed. oil conductivity, temperature, structure eliminated. effectiveness verified by comparative tests, error DP 20, 0.15%. research provide theoretical support on-site status.