XLPE电缆绝缘热老化的高压频域介电谱诊断方法

High Voltage Frequency Domain Dielectric Spectroscopy Diagnosis Method for Thermal Aging of XPLE Cables

热老化是导致XLPE电缆绝缘性能下降的重要原因,实现热老化的诊断对电缆安全具有重要意义,为此该文对XLPE电缆整体和局部热老化高压频域介电谱特性进行研究。通过内外加热法制备了整体热老化电缆试样和用于模拟局部热老化电缆线段,分别在不同老化阶段检测了整体热老化、局部热老化段与完好电缆比值为10%、4%的10kV缺陷电缆的高压频域介电谱(0.01~0.1Hz,最高检测电压U_(0)),分析了局部老化段占比对介电常数的影响,定义并分析了曲线分层度L、斜率、曲线积分和非线性度η。研究结果表明:高压频域介电谱对整体、局部热老化反应灵敏;具有一定老化程度的整体热老化、局部热老化缺陷电缆试样的L均大于1,L矩阵可作为电缆老化现象的诊断参数;较高检测电压等级(1.0U_(0))介电谱曲线的η对老化程度的变化敏感,且受局部缺陷占比影响较小,可以作为电缆老化程度的诊断特征;局部老化段的占比减小会使高压频域介电谱出现分层对应的时间延后,介电谱曲线积分值、曲线斜率减小,可以结合η的数值及曲线积分、斜率值所在数值区间判定电缆是否为局部老化;介电谱曲线是否出现迟滞现象可以作为区分XLPE电缆热老化和水树老化的依据。

Thermal aging is the important reasons for the degradation of XLPE cable insulation.The timely detection and treatment are of great significance for system operation safety.The research on diagnosis of XLPE cable overall and local aging using high voltage frequency domain spectroscopy(FDS)is carried out.The high voltage FDS(0.01Hz~0.1Hz,detection voltage up to U0)of 10 kV cables with overall length,with ratio of local thermal aging section to intact cable of 10%and 4%at different thermal aging stages are measured.Besides,the layering degree of the high voltage FDS curves L,slope and integral,and nonlinearityηare defined and analyzed.The effects of local aging ratio on the dielectric parameters are also studied.The results show that high voltage FDS is sensitive to both overall and local thermal aging,The L parameters of cable samples with overall and local thermal aging defects with a certain degree are greater than 1,so L matrix can be used as the diagnostic parameter of cable aging.Nonlinearityηis sensitive to the change of aging degree,and it is less affected by the proportion of local defects,so it can be used as a diagnostic characteristic of cable aging degree.With the decrease of the aging section proportion,the curves show layered characteristics later,and the integral value of dielectric spectrum curve and the slope of the curve are reduced.It can be determined whether the cable is thermal aged by combining the value ofηand the range of slope and integral.The hysteresis phenomenon can be used as basis to distinguish thermal aging and water tree aging of XLPE cable.