Study On Microstructure Evolution Process Of Silicone Rubber Used For Composite Insulators With Actions Of Electric Field And Temperature

Composite insulator's surface will meet higher field intensity due to continuous improvement of operating voltage level,which may lead to higher temperatures during processes of partial discharges.Under effects of high electric field and high temperature,aging problems of composite insulators will be more prominent.However,current researches mainly focused on the aging of composite insulators by high voltage experiments,and then deduced aging states from macroscopic characterizations.But they failed to reflect structural evolution processes of materials under effects of electric field intensity and temperatures.In view of this,the thesis selected the high temperature vulcanized silicone rubber used for composite insulators as the object.Based on the molecular simulation method,changes of the micro characteristics of the material during different temperatures and electric field intensities were analyzed,and the evolution process of silicone rubber's micro structure was explored.The results could provide a theoretical basis for relationships between the micro morphology and macro characteristics,which could provide further references for the fine assessments of aging states of composite insulators and optimizations of substrates.The results showed that the electric field intensity had the most significant effect on bond lengths and potential energy of molecular chains.When the electric field increased gradually,atoms of silicone rubber moved violently and bonds of molecular main chains elongated,while crosslinking bonds shortened.The main chains spiralized and curled significantly,it even shrunk into a cluster at the end of chains resulting in the reduction of molecular potential energy.The total energy was mainly affected by the potential energy,and the depletion of the two were all serious at 0.0025V/?.Accordingly,elastic moduli of silicone rubber increased gradually as well as hardness,thus aging cracks were apt to occur.However,the extremely high field intensity decreased the elastic constants greatly as well as the stiffness,so the mechanical load capacity was poor.Temperature had the most prominent effect on atomic motions,molecular kinetic energy and bond angles.When the temperature increased,the molecular main chains did not move significantly,but the movement of silicone rubber atoms were strengthened.The main chain absorbed energy and stretched while the bond angles increased.The molecular kinetic energy,potential energy and total energy increased linearly.Therefore,although the elastic properties of silicone rubber were poor at low temperatures,it could be improved by rising temperature,so the texture of materials became soft.With the further increase of temperature,the elastic modulus fluctuation and stiffness of silicone rubber rose.However,the extremely high temperature would reduce elastic properties greatly,the resistance of silicone rubber to deformation was also weakened.Accompanying,mechanical properties were degraded.Under the synergistic effects of electric field and temperature,the interaction of the two were weakened or strengthened sometimes,which resulted in the fluctuation in micro characteristics of silicone rubber.During the process,the motions of silicone rubber atoms were weakened,but the helical crimping shrinkage of molecular chains were obvious.When the temperature was too low or too high,enhancing actions of electric field intensity could improve molecular energies of silicone rubber.At lower temperatures,the elastic moduli of silicone rubber increased first and then decreased with rising electric field intensity,thus the material's stiffness increased first and then weakened.When the temperature was increased further,the rising electric field was weakened by temperatures,therefore,the elastic moduli decreased gradually,as well as stiffness and mechanical properties.Especially,when the electric field was about 0.0025V/? at 293 K,the synergistic effects destroyed molecular energies of silicone rubber seriously,so the elastic moduli were the smallest.Accordingly,mechanical properties of silicone rubber used for composite insulators declined severely.