Experimental Study of the Aged States Effects on Pressboard PDC Characteristics
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摘要: 为研究纸板劣化对其极化去极化电流(polarization and depolarization currents,PDC)特性的影响,在实验室内对油浸变压器绝缘纸板进行加速热老化,在不同老化阶段取出纸板试品,对不同老化状态的纸板进行石油醚萃取变压器油和真空干燥处理。为了表征绝缘纸板的老化状态,对各老化阶段的纸板采用粘度法测量聚合度,并使用扫描电子显微镜(scanning electron microscope,SEM)观察纤维素表面的微观结构及破坏状况。在同一温度下,对干燥后不同老化状态的纸板分别进行真空中和新变压器油浸渍条件下的PDC测量。结果表明,随着老化时间的延长,纸板聚合度下降,纤维表面微观结构破坏明显。纸板劣化造成真空中和油浸渍的纸板极化去极化电流显著增大,电导率增加,并导致其绝缘电阻降低,吸收比减小。因此,对于油纸绝缘,除老化产生的水分外,纸板劣化本身也将导致纸板电导率的增大,并显著影响其极化去极化电流的测量结果。Abstract: To investigate the effect of pressboard aged states on its polarization and depolarization currents（PDC） characteristics,the oil-impregnated pressboard samples were accelerated thermally aged for different time intervals.The pressboard samples of different aged states were sequentially put into petroleum ether as de-oiling solvent for residual oil removal,and dried in a vacuum oven to remove the petroleum ether and moisture.To characterize the aging status of different samples,the degree of polymerization（DP） was measured by viscosimetry and the scanning electron microscope（SEM） was also implemented to observe the surface microstructure.Then PDC tests were performed on each water-removed pressboard sample in vacuum and new oil impregnated ambient,respectively.Experimental results show that,with the aging status heavier and decreasing DP values,microstructure of cellulose fiber is significantly destroyed.Aged samples exhibit higher polarization and depolarization currents,lower insulation resistance and smaller absorptance in both ambient.It is confirmed that,for oil-paper insulation,besides the influence of water induced by aging,the deterioration of cellulose itself also causes the increasing of pressboard conductivity,and hence greatly affects the PDC test results.
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