Research On The Thermal Aging Properties Of Nonlinear Silicon Rubber

High-voltage direct current(HVDC)transmission technology has the advantages of large transmission capacity,long transmission distance,narrow transmission line corridors,asynchronous connection between power grids,high stability,low active power loss and good controllability.HVDC transmission has been widely used in the occasions of large capacity,long distance transmission lines and asynchronous AC system interconnection,etc.Along with the HVDC transmission technology is widely used in power grid,cable accessories(terminal and joint),as the main equipment of HVDC transmission system has also been widely used.However,the uneven distribution of electric field in the cable accessories is extremely easy to induce the electric field distortion.Compared with the cable,the failure probability of cable accessories is much higher.So the terminal and joint become the weakest part of high voltage cable application,and the performance will directly relate to the operation safety of the HVDC cables.In recent years,silicon rubber was widely used as high-voltage cable accessories due to the excellent insulating performance,good mechanical performance,wide range of working temperature,easy processing and molding,etc.And nonlinear silicon rubber composites can solve the problem of the electric field distortion in the cable accessories.But during the process of its operation,nonlinear silicon rubber composites will degenerate affected by the factors such as heat,electricity,and oxygen,which will reduce the service life of HVDC cable accessories.If the aging degree of HVDC cable accessory materials can not be assessed in time,it will easily result in the breakdown of accessories insulation,reduce the stability of HVDC cables,and endanger the power supply safety and reliability of the whole electric power system.Therefore,it has extremely important engineering significance but also economic and social benefits to study on the thermal aging properties of nonlinear silicon rubber and analyze the thermal aging mechanism.In this dissertation,the accelerated thermal aging experiments were performed on nonlinear silicon rubber as HVDC cable accessory insulation materials under the temperature of 130?,150? and 170?.Conductivity,DC breakdown strength,space charge,dielectric constant and dissipation factor,surface morphology,swelling index,thermal gravity analysis(TGA),tensile strength,thermal elongation of nonlinear silicon rubber insulation materials were tested under different aging time.The effect of thermal aging on electrical properties,physical and chemical properties,and mechanical properties of nonlinear silicon rubber insulation materials was studied.The results indicated that the thermal degradation reaction and cross-linking reaction existed at the same time during the thermal aging process of nonlinear silicon rubber.The cross-linking reaction played a primary role in the initial stage of thermal aging,and the conductivity properties,space charge distribution,surface morphology,crosslinking degree and mechanical properties of nonlinear silicon rubber materials all did not deteriorate.With the increase of aging time,thermal degradation reaction was dominant,and thermal aging created an obvious destructive effect on the electrical properties,physical and chemical properties,and mechanical properties.