Stress-thermal aging properties of silicone rubber used for cable accessories and electric-thermal-stress multiple fields coupling simulation

Abstract

During the long-term operation of a cable, the electrical field, high temperature, and interface stress may age or deteriorate the silicon rubber (SIR) insulation of the cable accessories, affecting the combined electrical-thermal-force performance of the accessories, and easily causing discharge faults. In this work, the electrical-thermal-force properties of silicone rubber for cable accessories under thermal aging and combined force-thermal aging are studied experimentally and numerically. The changes and mechanisms of physical and chemical properties, electrical properties, thermal properties and mechanical properties of silicone rubber are tested and compared before and after aging. The changes of electric, thermal and force field of cable accessories, caused by the change of SIR material parameters under different aging time and aging form, are further simulated. The experimental results show that the crosslinking degree and molecular motion system of SIR will change with the deepening of the aging degree, which will change the electrical-thermal-force properties of the material to different degree. After aging, large agglomeration protrudes and small cavities appear in SIR section, and the damage is more serious under force-thermal aging. The relative dielectric constant first decreases and then increases with the aging time increasing. The volume resistivity, breakdown strength and flashover voltage all first increase and then decrease. The thermal conductivity first increases and then decreases with aging time increasing. In addition, with the increase of aging time, the tensile strength and elongation at break decrease gradually. Considering the change of properties after aging, the destruction of SIR material by force-thermal aging is more serious. The simulation results show that under the two aging modes, the maximum electric field strength at the stress cone root of the cable accessories first increases and then decreases with the increase of time. The electric field strength at the stress cone root of the cable accessories, caused by the force-thermal aging, changes little, maintaining about 2.2 kV/mm. The difference in temperature between the inside and the outside of the insulation layer is obvious under different aging degree, and the temperature difference shows a first decreasing and then increasing trend under both aging modes, and the maximum temperature gradient is 9.15 ℃. The interface stress at the stress cone root decreases from 0.263 to 0.230 MPa, which is about 12.5% lower. This work has guiding significance in evaluating the insulation performance and analyzing the fault of distribution cable accessories.