500 kV海缆工厂接头绝缘恢复过渡区形成过程及电树枝特性

Formation Process and Electrical Tree Characteristics of Insulation Recovery Transition Zone of Factory Joints in 500 kV Submarine Cable

工厂接头是实现大长度海缆线路的关键技术,其中绝缘恢复工艺对工厂接头的绝缘介电性能及安全可靠运行起着重要的决定作用。首先利用流体仿真技术模拟了500kV交联聚乙烯(XLPE)海缆工厂接头绝缘注入形成过程;构建了透明可视化注塑平台系统,对工厂接头的注塑形成过程进行了物理模拟;探讨了海缆工厂接头绝缘恢复过渡区的形成机理;利用偏光显微镜对500kV海缆工厂接头的过渡区微观形态进行了研究;对500kV海缆本体绝缘、工厂接头恢复绝缘及过渡区的绝缘样品电树枝起树电压及电树枝生长特征进行了试验研究。研究结果表明:模具内注入的低密度聚乙烯熔体流动方向的垂直面上存在一定的速度梯度分布,是导致500 kV海缆模塑接头过渡区形成的重要原因;透明可视化注塑模拟过程与流体仿真注塑过程基本一致,进而验证了熔体流动仿真结果的可靠性;工厂接头的绝缘恢复过渡区的切片样品表面存在大量不规则应力裂痕;典型过渡区样品电树枝形貌显示出异于正常电树枝的生长特征,长宽比接近0.7,且具有不沿电场方向生长的特征;工厂接头过渡区样品的电树枝起始电压对比本体绝缘样品降低约30.76%。

Factory joint is the key technology for long-length submarine cable lines.The insulation recovery process of factory joint plays an important role in determining the overall insulation dielectric performance and safe and reliable operation of long submarine cable lines.Consequently,we adopted computer fluid simulation technology to simulate the insulation recovery formation process of 500 kV cross-linked polyethylene(XLPE)submarine cable factory joints.Moreover,we built a transparent visual injection molding platform system,simulated and recorded the injection molding process of molded factory joints,and characterized the formation mechanism of factory joint insulation recovery transition zone.Meanwhile,we characterized and studied the transition zone of 500 kV submarine cable molded joint by polarized light microscope,and comparatively investigated the 500 kV submarine cable factory joint body insulation,recovery insulation and transition zone insulation sample electric branch,tree voltage and electric tree branch growth characteristics.The research results show that there is velocity gradient distribution on the vertical plane of the low-density polyethylene(LDPE)melt flow direction in the mold.The velocity gradient distribution is the reason of the formation of insulation transition zone.The transparent visual injection molding simulation process is basically consistent with the fluid simulation injection molding process,indicating the reliability of the melt flow simulation results.Microscopic observations show that there are a large number of irregular stress cracks on the surface of the sliced sample in the factory joint transition zone.The electrical branching morphology tests to transition zone show that the growth characteristic is different from that of the normal electrical branch,and the aspect ratio is close to 0.7.The growth of electric tree branches has the characteristics of not growing along the direction of electric field.The initial voltage of the electrical branch of the transition zone sample is reduced by about 30.76%compared with the cable insulation sample.