中文摘要：

目前针对换流变压器油纸绝缘直流局部放电特性的研究成果较少,且缺乏相关研究标准及理论依据。为此,在80℃环境温度下,对典型油纸复合绝缘缺陷模型在直流电应力作用200 h内的长期局部放电单一脉冲信号的时域、频域信号变化规律进行了分析,统计了直流局部放电信号不同发展阶段的等效时频特征;并采用扫描电镜观察绝缘纸板表面形貌特征,利用原子力显微镜观测绝缘纸板表面粗糙度的变化规律;采用ANSYS电场仿真法研究了绝缘纸板表面最大电场强度与其表面最大偏差的关系,并率先在国内外建立起两者之间的定量函数。试验结果表明,随着加压时间的增加,单一放电脉冲的上升时间逐渐增大,从几ns增大至数μs;放电脉冲电流值也随之增大,由数百mA增大至数A。随着老化时间的延长,绝缘纸板表面纤维素分子逐渐断裂,使得纸板表面逐渐电蚀碳化,其粗糙度也相应逐渐增大,进而对绝缘纸板造成严重损伤。此外,纸板粗糙度的增大会引起电场畸变,更易诱发局部放电。

英文摘要：

The DC partial discharge（PD） characteristics of oil-paper insulation in converter transformer and the related theoretical basis and standards are seldom researched. Therefore, we analyzed the change of time-domain and frequency-domain signals of single-pulse PD signals in a typical defect model of oil-paper composite insulation under DC stress at 80 ℃ for 200 hours, and statistically obtained the equivalent time-frequency characteristics of DC PD signals in different stages of PD development. We also observed the topography characteristics and the roughness change of insulating cardboard surface by the scanning electron microscopy and atomic force microscopy, respectively. Finally, we established the relationship between the maximum electric field strength and the maximum deviation of insulating cardboard surface through electric-field simulation in ANSYS, and built the first corresponding quantitative function. The results indicate that with the increase of stressing time, the rise time of single discharge pulse increases from several nanoseconds to several microseconds, while the current amplitude increases from several hundred microamperes to several amperes. Moreover, with extending aging time, the cardboard surface gets electric eroded and carbonized due to the break of cellulose molecules. Hence its roughness increases which further causes damage of insulating cardboard, distortion of electric field, and eventually the occurrence of PD.