中文摘要：

为了更加深入地了解换流变压器中交直流叠加电压下油纸绝缘的沿面闪络问题,通过搭建直流电压分量可以任意调节的交直流叠加电源系统,研究了具有背面电极和不具有背面电极这2种结构下油纸绝缘的沿面闪络问题。试验结果表明：在复合电场下,有背面电极时,沿面闪络电压比无背面电极时稍低;在2种结构下,沿面闪络电压均表现为纯交流电压时最低,随着直流电压分量的增加,沿面闪络电压也逐渐增加。此外为分析油纸绝缘界面的影响,还研究了相同电极结构下纯油的击穿电压。对比分析纯油的击穿电压和油纸绝缘的沿面闪络电压后发现：直流电压分量较低时,油纸绝缘界面的存在降低了该结构的击穿电压;而直流电压分量较高时,油纸绝缘界面的存在反而稍微提高了该结构的击穿电压。最后从复合电场分布的特点出发,分析了不同直流电压分量下油纸绝缘的沿面闪络过程。分析后认为：直流电压分量较小时,电极附近电场强度较高,导致油易于电离并产生大量载流子,从而促进了油纸沿面闪络的发展;而随着直流电压分量的变大,电场分布将变得不同,其沿面闪络电压升高;同时,上述电场分布的特点也是造成直流电压分量较低时沿面闪络电压低于纯油击穿电压的原因。

英文摘要：

For further understanding creepage flashover in converter transformers, we studied the creepage flashover under oil-paper insulation of two electrode structures which were in the presence and absence of the back electrode, and adopted a power supply for composite AC and DC voltage to provide an adjustable percentage of DC voltage. The results showed that the flashover voltage in the presence of the back electrode was lower than that in the absence of＇the back electrode. Furthermore, for both electrode structures, there was the lowest flashover voltage under pure AC voltage, and the flashover voltage increased with DC component of the composite voltage. Besides, to find out the effect of interface of oil-paper insulation, flashover voltages of pure oil under the same electrode structures were also studied. The breakdown voltage of pure oil was compared with that of oil-paper insulation. The comparison showed that, when DC component was relatively low, the breakdown voltage was decreased by the interface of oil-paper, yet it would be increased by the interface if the DC voltage component was large enough. From composite AC and DC electric field point of view, when DC component was low, there would be larger electric filed around the electrode, leading to the oil molecules ionizing that produced a large amount of current carriers, and then promoted the development of creepage ftashover. However, with the increase of DC component, the electric field distribution would change and the creepage flashover voltage would increase. At the same time, the electric field distribution mentioned above also caused the fact that the flashover voltage was lower than breakdown voltage when DC component was relatively low.