中文摘要：

为研究直流电压下油纸绝缘中局部放电的超高频特性，组建了一套直流电压下局部放电试验系统以及由局放超高频检测和超宽带检测组成的测量系统，其中脉冲电流超宽带检测的作用是确保超高频检测获取的信号来自于试品自身的局部放电。试验设计了6种油纸绝缘局放模型以模拟换流变压器的典型缺陷，并引入毫瓦分贝（DBM）频谱分析对超高频信号进行了统一化处理，以比较不同缺陷模型对应的超高频信号。直流下试验结果表明：局部放电电流脉冲具有极快的上升沿，能激励起大于300MHz的超高频电磁波，它可以通过超高频传感器加以耦合接收。各种缺陷模型局部放电的DBM频谱分布各异，超高频段能量幅值最大处也不一样。因此若想以高信噪比实现直流下局部放电超高频信号的在线监测，需要使用中心频率可调的窄带滤波器。这些特性为直流输电系统中使用油纸绝缘的电工设备进行局部放电超高频信号在线监测提供了试验依据。

英文摘要：

To study Ultra-high-frequency （UHF） characteristic of partial discharge （PD） in oil-paper insulation under DC voltage, a test system with Ultra-wideband （UWB） and UHF detection technologies developed to measure PD under DC voltage is introduced in this paper. The role of UWB detection of PD pulse current is to ensure that the UHF signals are generated by the specimen＇s own PD. According to the analysis of defects in oil-paper insulation of converter transformer, six corresponding PD models are designed including needle to plate, internal defect and floating electrode, et al. The UHF sensor is tested by the PD pulse of corona model under DC voltage, which shows a good result that there is no signal picked up by the sensor. And the experimental results of PD detection under DC show that the PD current pulses have a very short rise-time, which are capable of generating UHF signals at frequencies up to at least 300 MHz, and these electrical magnetic waves can be picked up by the UHF sensor. In order to be able to make comparison for those UHF signals of the various defects, a unified processing named DBM spec- trum analysis method is presented. The analysis results show that the DBM spectrums differ with various defects, the maximum amplitudes of the energy distribution against the UHF are also different, which indicates the on-line monitoring for the UHF PD signal under DC should be realized utilizing the narrow-band filter with adaptive center frequency. This provides a test evidence for further study on on-line monitoring technology for UHF PD signals under DC voltage.