基于蠕变模型的水树老化电缆绝缘自恢复机制

Insulation Self-recovery Mechanism of Water Tree Aged Cables Based on a Creep Model

为了更准确地评估水树老化电缆的绝缘状态,研究了水树老化电缆出现的绝缘自恢复特性与水树微观结构变化之间的关联,并提出了基于蠕变模型的绝缘自恢复机制。在电缆的加速水树老化过程中,介质损耗因数及泄漏电流值随老化时间的增加而逐渐增大,老化区域出现明显水树枝,当撤离外施电压一段时间后,二者均有所下降,出现了绝缘自恢复现象。通过构建"珍珠串"有限元仿真模型和四元件蠕变模型,研究了水树微观结构变化同水树生长及自恢复之间的关系,并计算分析了水树蠕变过程对介质损耗因数及泄漏电流的影响。研究表明,在没有外施电压作用时,水树的蠕变过程使得水树通道关闭、水树空洞缩小,导致介质损耗因数和泄漏电流下降。因此,水树蠕变过程是电缆绝缘自愈的主要原因。

To accurately evaluate the insulation condition of water tree aged cables, this paper addresses the relationship between the self-recovery properties of insulation and the microstructure changes in water tree aged cables, and a mechanism of insulation self-recovery is presented based on a creep model. During the process of accelerated water tree aging, the dielectric loss factor and the leakage current increased with the aging time, and the water tree branches can be clearly observed in the aging area. However, the two electrical parameters decreased when the applied voltage was removed from the aged samples, and a self-recovery phenomenon of insulation appeared. Based on the ＂string of peals＂ model and the four-element creep model, the relationship between the changes of water tree microstructure and the water tree self-recovery phenomenon was investigated. According to the results of electric field simulation and the creep theory, the effect of the creep process on the dielectric loss factor and the leakage current was also analyzed. The results show that the water tree self-recovery phenomenon is closely related to the changes of water tree microstructure. During the period without applied voltage, the creep process of water tree leads to closing of water tree channels and shrink of water tree voids, which can lead to the reduction of the dielectric loss factor and the leakage current. Therefore, the water tree creep process is the main reason for the cable insulation self-recovery.