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Study on Degradation Diagnosis for Power Cable Using Wavelet Analysis of Pressure Wave Produced by Electrical Tree Propagation

电树传播压力波小波分析电力电缆老化诊断研究

基本信息

批准号：
15560246
负责人：
KITANI Isamu
金额：
$ 2.18万
依托单位：
Ehime University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

Treeing degradation diagnosis of electrical power cable was carried out using an AE method. Time-Frequency characteristics of pressure wave due to partial discharges in tree was calculated by continuous Wavelet transform. Results can be summarized as follows.Time-frequency analysis of pressure waves caused by an electrical tree from a point electrode in a low-density-polyethylene subjected to ac voltages. In the first case, the applied voltage was raised with 5 kV step at 5 minutes intervals. When a tree growth was started from the point electrode at 15kV, a high frequency pressure wave of about 8MHz was propagated from the tree. When the tree became large and more bushy, the high frequency pressure wave from the tree tip was followed by a lower frequency pressure wave from the tree stems. In the second case, a constant voltage of 25 kV was applied to the sample for 4 hours. Both the high frequency pressure wave and the following lower frequency pressure wave became larger at the first … More stage. However, the lower frequency pressure wave disappeared when the treeing degradation was attained to a critical level. This was because the carbonization of the tree wall was caused by the partial discharges. These results demonstrated that the time-frequency characteristics of the pressure waves were directly related to the partial discharge behavior in tree.Pressure waves from a block sample which was composed of low-density-polyethylene (LDPE) and ethylene-ethylacrylate (EEA) were measured by an AE sensor on the back of the plane electrode. Results of the time-frequency analysis of the pressure signal showed that a high frequency pressure wave due to partial discharge at the front area in the tree was followed by a lower frequency pressure wave due to partial discharge near the point electrode. In a sample of LDPE alone without EEA, only the lower frequency pressure wave disappeared when the treeing degradation proceeded to a critical level. The disappearance suggested that carbonization at the rear area in the tree was caused by repetitive discharges. However, the disappearance phenomenon did not observed for a LDPE/EEA blended sample. We confirmed that there was an optimum blend ratio between LDPE and EEA for the inhibition of carbonization.Pressure waves from a void in LDPE alone was measured at various positions. When the AE sensor was set just below the void, pressure waves was directly propagated to the sensor. However, the direct component was not detected when the position of the sensor was moved along the plane-electrode surface, so that the time-frequency characteristics was greatly changed. We concluded that the location of the void can be deduced from the result of the time-frequency analysis. Less

采用声发射方法对电力电缆的树枝化退化进行了诊断。利用连续小波变换计算了树木局部放电压力波的时频特性。研究结果可归纳如下：交流电压作用下低密度聚乙烯中点电极电树引起的压力波的时频分析。在第一种情况下，施加的电压以5分钟的间隔以5 kV的步长升高。当树木从15 kV的点电极开始生长时，从树木传播约8 MHz的高频压力波。当树木变得更大，更浓密，从树尖的高频压力波是由一个较低的频率压力波从树干。在第二种情况下，对样品施加25 kV的恒定电压4小时。高频压力波和随后的低频压力波均先增大后减小 ...更多信息阶段当树枝化降解达到临界值时，低频压力波消失。这是因为树壁的碳化是由局部放电引起的。采用平板电极背面的声发射传感器测量了由低密度聚乙烯（LDPE）和乙烯-丙烯酸乙酯（EEA）组成的块状试样的压力波，并对压力波的时频特性进行了分析。压力信号的时频分析结果表明，由于在树的前部区域的局部放电的高频压力波，其次是由点电极附近的局部放电的低频压力波。在没有EEA的单独LDPE样品中，当树枝化降解进行到临界水平时，仅较低频率的压力波消失。这种消失表明，树木后部的碳化是由重复放电引起的。然而，对于LDPE/EEA共混样品，没有观察到消失现象。我们证实了LDPE和EEA之间存在一个抑制碳化的最佳共混比。当AE传感器设置在空隙正下方时，压力波直接传播到传感器。然而，当传感器的位置沿平面电极表面沿着移动时，直接分量检测不到，从而时频特性发生了很大的变化。我们的结论是，空洞的位置可以推断出的时频分析的结果。少