Compression stress relaxation characteristics and failure mechanism of silicone rubber for high voltage cable accessories

Sufficient interfacial pressure between silicone rubber (SIR) insulation and cross-linked polyethylene (XLPE) in high-voltage cable accessories is the basic condition to ensure the normal operation of cable accessories. However, in the actual operation of cables and accessories, high-temperature aging and mechanical aging can cause the mechanical properties of SIR materials to decline, thus affecting the size of the insulation interface pressure. Firstly, the relaxation law of compressive stress of SIR material is obtained by measuring the compressive stress under force-thermal synergistic aging. Secondly, the time-temperature equivalent model is established according to the measured data to evaluate the service life of the cable accessories. Thirdly, the physical and chemical properties of SIR with different aging times are tested to analyze the change in its mechanical properties. Finally, the effect of temperature on the stress relaxation characteristics of SIR is calculated from the microscopic level by molecular simulation. The experimental results show that the compressive stress of SIR decreases first and then becomes stable with the increase of aging time due to the movement of molecular chains and chemical reactions in SIR. In addition, the compression stress relaxation rate of SIR increases with temperature. The aging life prediction model shows that when the relaxation coefficient of compressive stress drops to 50% of the initial value at the end of cable life, the service life of cable accessories at 70°C is about 24 years. The molecular simulation shows that the relaxation of the molecular chain of SIR is accelerated with the increase in temperature, and the stress relaxation of SIR material is accelerated on a macroscopic level. This research can provide a theoretical basis for the design and operation reliability of cable accessories.