基于损耗电流谐波特征分析的XLPE电缆局部尖刺缺陷诊断

Diagnosis of XLPE Cable Local Tip Defects Based on Analysis of Harmonic Characteristics of Loss Current

实现电缆局部缺陷的在线诊断对电力系统的稳定运行具有重要意义。损耗电流的谐波分量蕴含丰富的绝缘信息且满足现场带电检测的需求,是极具前景的可实现在线监测与诊断的检测手段。该文开展了基于损耗电流谐波特征分析的电缆尖刺缺陷诊断研究,主要分为仿真机理研究和针对典型局部缺陷的实测研究两部分。首先,对XLPE材料在高电场下的电导特性进行了仿真分析,建立了非线性伏安关系的XLPE电导模型,分析了不同尖刺曲率半径和电极间距对损耗电流谐波特征及电导率的波动程度的影响;然后,制作了三种规格的XLPE电缆导体尖刺缺陷模型并开展了实测研究;最后,对比分析了仿真分析和实测结果。研究结果表明:绝缘存在尖刺缺陷的电缆存在高次谐波分量,其主要成分是3次与5次谐波分量;缺陷导致了高电场,由此产生的非线性伏安特性是高次谐波分量出现的主要原因。对比分析结果表明,损耗电流的谐波畸变率和电导率畸变率与尖刺的曲率半径及电极间距成反比,导体尖刺缺陷的严重程度和缺陷形貌的改变,都会使得损耗电流中的谐波成分发生改变;损耗电流总谐波畸变率(THD)和各次谐波贡献率Hn是有效的诊断特征量。

The online diagnosis of local defects in cables is of significant importance for ensuring the power systems stable operation. Given its rich insulation information and compatibility with on-site detection requirements, the harmonic component of the loss current has been recognized as a highly promising detection method for achieving online monitoring and diagnosis. This article aims to explore the online diagnosis for cable local tip defects by analyzing the harmonic characteristics of the loss current In order to investigate the XLPE nonlinear conductivity phenomenon under high electric fields, a simulation model based on the carrier transport process has been developed to analyze the spike defect loss current density. The concepts of the total harmonic distortion (THD), the harmonic contribution rate (Hn) and the conductivity distortion rate (CDR) are introduced to describe the frequency domain characteristics of the loss current and to quantitatively measure the fluctuation degree of conductivity, respectively. To assess the defect severity influence on the harmonic characteristics of loss current density and the conductivity fluctuation, simulation analyses are performed under varying circumstances. The findings reveal that spike defects in XLPE lead to the presence of higher-order harmonic components in the loss current density, mainly the 3rd and 5th harmonics. The conductivity fluctuates synchronously with changes in power frequency voltage. Decreasing the curvature radius of the needle tip from 40 μm to 25 μm can result in 50.75%, 68.63% increase in THD and CDR, 18.63% decrease in H3 (the contribution rate of the 3rd harmonic), and 15.62%, 6.42% increase in H5 and H7 (the contribution rate of the 5th and 7th harmonic). Reducing the electrode spacing from 4mm to 3mm leads to 57.39%, 83.46% increase in THD and CDR, 20.69% decrease in H3, 14.41%, 6.42% increase in H5 and H7. Further analysis of the relationship between THD, CDR, and Hn indicates that the conductivity fluctuation causes the superposition of higher-order harmonic components. Specifically, The greater the fluctuation of conductivity over time, the higher the harmonics content, as well the proportion of 5th and 7th harmonic components. To examine the harmonic characteristics of the actual XLPE insulation spike defect loss current, a detection platform has been established for spike defect samples. The loss current of three different sample specifications has been measured and analyzed, and the results have been compared with the simulation results. The analysis demonstrates the good consistency between the simulated and measured results regarding the harmonic components of the loss current under varying defect severity levels. Furthermore, the measured results indicate that as the defect severity increases, the contribution rate of the 3rd harmonic gradually decreases, while the contribution rates of the 5th and 7th harmonics gradually increase, which is consistent with the simulation results. The harmonic characteristics analysis of the loss current proves effective for diagnosing local spike defects in cables, with the harmonic composition closely linked to the morphology of sharp defects. Based on comprehensive simulation and measurement studies on typical local sharp defects, the following main conclusions can be drawn: (1) The presence of a local spike defect in the cable leads to the existence of higher-order harmonics in the loss current, mainly the 3rd and 5th harmonics. (2) THD, as a diagnostic feature, exhibits the clear correlation with defect severity and can serve as a quantifiable parameter for assessing the severity of cable defects. (3) Comparative analysis results indicate that the severity and morphology of spike defects affect the harmonic components in the loss current. Specifically, higher defect severity and sharper spike shapes result in lower proportion of the 3rd harmonic and higher proportion of 5th and 7th harmonic.