高压频域介电谱诊断XLPE电缆局部绝缘老化缺陷的研究

Local Aging Diagnosis of XLPE Cables Using High Voltage Frequency Domain Dielectric Spectroscopy

热老化和水树老化是导致交联聚乙烯(XLPE)电缆绝缘性能下降的重要原因,及时发现和处理热老化和水树老化缺陷,对于电缆安全运行具有重要意义。为了解决超低频(0.1Hz)介电损耗检测对电缆局部老化检测灵敏度不高、无法实现老化缺陷类型区分的问题,开展高压频域介电谱诊断XLPE电缆绝缘老化缺陷的研究。通过加速老化,制备了水树老化和热老化电缆线段,在不同电压等级下检测27.4m长10kV电缆局部老化前后的频域介电谱(0.01~0.1Hz),构造和分析介电谱曲线的分层度S和迟滞度D,并与超低频(0.1Hz)介电损耗检测的方法进行比较。研究结果表明,超低频难以发现局部热老化和70%贯通的局部水树老化缺陷,而高压频域介电谱对局部热老化和局部水树老化反应灵敏;局部热老化和局部水树老化缺陷试样的曲线分层度S均大于1,可作为电缆老化的判断依据;局部水树老化试样的曲线迟滞度D显著大于局部热老化试样,可以作为XLPE电缆局部热老化和局部水树老化区分的特征量。

Water tree aging are important reasons for the degradation of XLPE cable insulation.The timely detection and treatment of those aging defects are of great significance for system operation safety.Although very-low frequency(VLF,0.1Hz)dielectric loss detection is widely used for the cable aging detection,it has low sensitivity for local defects and cannot distinguish the aging defects types.In this paper,high voltage frequency-domain spectroscopy(FDS)is carried out to diagnose XLPE cable insulation aging defects.Through the accelerated aging experiment,the water tree aging and thermal aging defective cable segments are prepared.Then the high-voltage dielectric spectroscopy(0.01~0.1Hz)under different voltage levels is detected on the 27.4m long 10kV cable before and after local aging.The dielectric parameters,layering degree S and the hysteresis degree D of FDS curve,are defined and analyzed.The FDS results are also compared with the VLF(0.1Hz)dielectric loss detection.The results show that the VLF method is difficult to find local thermal aging and 70%water tree penetration defects,while the high-voltage FDS is sensitive to local thermal aging and local water tree aging defects.It is found that the layering degree S of thermal aging and water tree aging samples is greater than 1,which can be used as the criterion of cable aging;the hysteresis degree D of the water tree aging sample is significantly greater than that of the thermal aging sample,which can be used as a characteristic quantity to distinguish thermal aging and water tree aging of XLPE cables.