电缆附件用硅橡胶力-热老化特性及电-热-力多物理场耦合仿真研究

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

长期运行过程中,高温及界面压力作用会导致电缆附件硅橡胶(silicon rubber,SIR)绝缘发生老化,影响附件材料的电-热-力综合性能,易引发放电故障.该文采用实验和仿真结合的方法,研究力-热联合老化作用下硅橡胶材料的电-热-力综合性能变化规律;进一步仿真研究了SIR材料参数变化引起的电缆附件电场、热场和力场变化.实验结果表明,随着老化程度的不断加深,SIR的交联程度和分子运动体系会发生变化,导致材料的电-热-力性能发生不同程度的改变.相对介电常数呈现先下降后上升的趋势,体积电阻率、击穿场强和闪络电压等均呈现先上升后下降的趋势;此外,随着老化时间的延长,材料拉伸强度和断裂伸长率逐渐下降.仿真结果表明,力-热联合老化引起的电缆附件应力锥根部电场强度变化较小,维持在2.2 k V/mm左右;不同老化程度下绝缘层内外侧温差较为明显,最大温度梯度为9.15℃;应力锥根部界面压力从0.263 MPa下降到0.230 MPa,下降约12.5%.该工作对于配电电缆附件绝缘性能评价和故障分析具有指导意义.

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 electricalthermal-force performance of the accessories,and easily causing discharge faults.In this work,the electricalthermal-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.