配电电缆本体受潮缺陷定位及受潮特性分析

Localization of Damp Defects and Analysis of Moisture Characteristics for Cable Body in the Distribution Grid

为解决现阶段极化/去极化电流法(polarization and depolarization current,PDC)和时域反射法(time domain reflectometry,TDR)无法对电缆本体局部受潮缺陷进行定位及识别受潮路径的问题,提出一种基于输入阻抗谱的配电电缆本体受潮缺陷定位方法,并对电缆本体受潮特性进行详细分析。首先,利用电缆分布参数模型、频域反射理论、输入阻抗谱、加窗傅里叶变换,阐述所提诊断定位方法的基本原理。接着,建立电缆本体受潮模型,运用短电缆样本受潮实验和仿真建模,详细说明电缆本体不同受潮严重程度、潮气扩散速率分别对电缆电容变化与样本含水量的影响。之后,运用仿真,对不同受潮程度、不同受潮区域范围的电缆局部缺陷进行定位诊断,得到不同受潮缺陷的定位反射特征。最后,在实验室20m长的10kV交联聚乙烯(cross-linked polyethylene,XLPE)电力电缆上制作0.8 m长的局部受潮缺陷,通过电缆本体受潮实验检验所提方法的有效性。仿真和实验结果表明:短时间内潮气很难径向入侵至电缆主绝缘,而会沿着铜屏蔽层与外半导电层之间的间隙往电缆首末两端轴向扩散。该方法不仅能对受潮区域大于1.7 m或受潮程度大于5%的电缆本体受潮缺陷有较好的识别效果(定位误差小于±5%),还能表征电缆本体受潮路径和潮气扩散速率。

In order to solve the problem that polarization and depolarization current(PDC)method and time domain reflectometry(TDR)method cannot locate the local damp defects and identify damp path for the cable body at present,this paper presented a new method based on input impedance spectrum to locate the damp defects in the distribution grid.The moisture characteristics of the cable body were analyzed in detail.Firstly,the basic principle of the proposed diagnosis and location method was briefly described by using the distribution parameter model of power cables,frequency domain reflection theory,input impedance spectrum,and windowed Fourier transform.Next,the damp model of cable body was established,and the experiment of short cable samples damped and the simulation modeling were used.Then,the effects of different damp degrees and moisture diffusion rate on the capacitance change and water content of the samples were described in detail for the cable.After that,the local defects of cables with different damp degrees and different areas were diagnosed by simulation,which obtained the location reflection characteristics of different damp defects.Finally,a 0.8 m long local damp defect was fabricated on a 20 m long,10 kV cross-linked polyethylene(XLPE)power cable in the laboratory.The effectiveness of the proposed method can be verified by the moisture experiment for the cable body.The simulation and experimental results show that moisture is difficult to invade into the main insulation of the cable radially,but it will spread along the gap between the copper shield and the outer semiconducting layer to both ends of the cable axially in a short period of time.This test method can not only identify the damp defects of the cable body with damp area>1.7 m or damp degree>5%(the localization error<5%),but also characterize the damp path and the moisture diffusion rate of the cable body.