运行老化XLPE电缆导体屏蔽层侧绝缘缺陷分析

Insulation Defects at the Side of Conductor Screen Layer in Service-aged XLPE Cables

运行老化交联聚乙烯(cross-linked polyethylene,XLPE)电缆导体屏蔽层侧的绝缘缺陷尚未引起充分关注。该文对新电缆及退运的老化电缆进行了超低频介损和微观理化性能对比测试,发现退运电缆处于严重老化状态,且导体屏蔽层侧的绝缘内部存在连续的片状老化缺陷。对退运电缆进行扫描电镜测试发现,导体屏蔽层与内侧绝缘层存在大量微孔。能谱分析证明,电缆老化后的导体屏蔽层及内侧绝缘中均有少量铝(Al)元素的存在。进一步采用红外光谱测试发现导体屏蔽层中的乙烯共聚物(ethylene-vinyl acetate copolymer,EVA)产生了老化降解,且内侧绝缘存在较为明显的羰基与羟基的红外吸收峰。因此,电缆运行过程中导体屏蔽层中的EVA可能存在一定程度的老化降解,降解产物进入绝缘内部参与XLPE的氧化降解反应,进而导致了导体屏蔽层侧的绝缘内部出现连续片状老化缺陷。

Insulation defects at the side of the conductor screen layer of service-aged cross-linked polyethylene(XLPE)cables have not attracted sufficient attention.In this paper,the very-low-frequency dielectric loss tests and microscopic physical and chemical properties analysis were respectively performed on new cables and service-aged cables.It is proved that the retired cables were seriously aged and continuous sheet ageing insulation defects could be found at the side of conductor screen layer.According to the scanning electron microscope(SEM)observation,some of micro voids exist in conductor screen layers and insulation layers of aged cables.Based on the analysis of energy dispersive spectrum,there is a small amount of aluminum in the conductor screen layer and the inner insulation.Besides,degradation of ethylene-vinyl acetate(EVA)copolymer in the conductor screen layer is verified according to infrared spectroscopy(IR)test results,and new absorption peaks of hydroxyl and carbonyl groups can be found in the infrared absorption spectrum.Therefore,degradation of EVA in conductor screen layer of service aged cables can take place during the operation process,and degradative products can get into the inner insulation,which can further participate in the oxidative degradation reaction of XLPE and further lead to the formation of continuous sheet aging insulation defects on the side of conductor screen layer.