中文摘要：

为研究油纸绝缘在直流电压下长期局部放电发展的过程，采用脉冲电流法对典型油纸绝缘缺陷模型在80℃环境温度中进行了200h的直流耐压试验，根据其统计分布的明显变化将直流局部放电划分为5个阶段；利用Novocontrol宽频介电阻抗谱仪对直流局部放电发展不同阶段的绝缘纸板的介电常数、体电导率及介质损耗因数的频谱特性进行测量，并通过x射线衍射仪及红外光谱分析仪对直流局部放电发展不同阶段的绝缘纸板的聚集态及表面官能团进行测定。研究结果表明：绝缘纸板介电常数频谱随加压时间会呈现下降趋势，主要原因是绝缘纸板纤维素分子在直流电场作用下其结晶度上升，分子排列逐渐规则，导致分子间距减小，使得纤维分子转向逐渐变得困难，引起绝缘纸板极化率下降；体电导频谱随加压时间增加而逐渐增加，这是由于绝缘纸板的结晶度的增加而导致纤维素分子间电子云重叠，电子在分子间迁移率增加，在外施电场作用下电子的运动更加容易，从而致使绝缘纸板电子电导增加；介质损耗因素随加压时间增加而逐渐减小，这是由于决定绝缘纸板介质损耗因数tanδ的纤维素分子葡萄糖基上含有极性基团-CH2OH，在电场和温度场的共同作用下，其在有氧环境中逐渐被氧化生成羰基基团，进而极性基的数量明显减少造成的。

英文摘要：

In order to study the DC partial discharge （PD） in oil-paper insulation, we used a pulse current method to conduct DC withstanding tests on typical oil-paper insulation defect model for 200 hours at 80 ℃. Due to the variation of statistical spectrums, DC PD was divided into five stages. Furthermore, using a Novocontrol broadband dielectric spec- trometer, we measured the dielectric constants, the bulk conductivity and the dielectric loss factor of insulation paper in different stages of PD. Besides, we used X-ray diffraction device and infrared spectrometric analyzer to measure the structure of molecular aggregation and the functional groups in the insulation paper. The results show that the dielectric spectra decrease with increasing stressing time. The reason for this is that in insulation paper affected by DC electric field, the crystallinity increases and molecules array grow regularly, which will lead to the decrease of space between molecules and consequently the difficulty of cellulose molecules to turn around as well as the decrease of dielectric conduction of insulation paper. The frequency spectrum of dielectric conduction decreases with PD time, since the increase in crystallin- ity of fiber molecules will result in the overlapping of electron clouds that further increase the mobility of charge carriers, and eventually increases the dielectric conduction. Plus, the dielectric loss factor, tanδ also decreases with time. This is because fiber molecules have polar functional groups --CH2OH, which will be oxidized and produce carbonyl groups in aerobic environment under electric stress and heat, and eventually decreases the amount of --CH2OH.