Experimental Study on the Influence of Extreme Liquid Medium on the Mechanical Properties of Polymer Insulation of High Voltage Cable Joints

The High voltage cable accessories have complex structures with multiple insulation layers, and are subjected to multi-field coupling and complex environmental effects, making their internal conditions more complex and the weakest link in the power cable system with a failure rate much higher than that of the cable body. Liquid medium is one of the main external factors affecting the polymer insulation of cables. Silicone rubber is the main insulation material of prefabricated power cable accessories. This paper studies the influence mechanism of different liquid medium invasion on the mechanical properties of vulcanized silicone rubber, including tensile strength, elongation at break, tear resistance, hardness, etc. The results show that after liquid medium invasion, the performance of silicone rubber decreases to varying degrees, depending on the type and concentration of the liquid. High concentration acid solutions have a greater impact on silicone rubber than salt solutions and low concentration acid solutions, and nitric acid solutions with a concentration greater than 1mol/L significantly reduce its mechanical properties. After immersion in nitric acid solutions, the mechanical properties of silicone rubber decrease significantly with increasing concentration, while hardness recovery even exceeds the original level. In this paper, XPS analysis method is used to study the changes of the chemical structure of the surface of silicone rubber before and after liquid invasion. It is found that high concentration acid solutions reduce the content of C element and increase the content of O element on the surface of silicone rubber. By using DMA analysis method to measure the viscoelasticity of silicone rubber material after immersion in solution, it is found that the glass transition temperature of silicone rubber decreases and the crosslinking degree decreases after immersion. The changes in the surface structure and internal crosslinking degree of silicone rubber after liquid invasion are the direct cause of its mechanical property changes.