| For the high-voltage cables,the insulation level is a key factor affecting their long-term operation safety.Silicon rubber(SR)has good machinability,corrosion resistance and adhesive properties,is commonly used as the reinforced insulation components for stress cones in cable accessories.In the interior of cable accessories,the local electric field distribution is extremely uneven because the conductivity and other parameters of insulating materials cannot achieve continuous transition,while the presence of internal and external temperature differences further exacerbates the non-uniformity of electric field distribution.The local field strength borne by the insulation part of the accessory is much higher than the average value,it is easy to cause partial discharge within the equipment,and even directly cause insulation failure in severe cases,posing a great threat to the safe operation of power system equipment.Reducing the local high field strength at key locations and promoting the rapid release of accumulated heat energy is an important issue in the insulation design of high-voltage cable accessories.Using functional SR materials with adaptive electrical conductivity changes with the electric field as accessory insulation is an effective technical way to regulate local electric field distribution.However,there is a contradiction between nonlinear conductivity regulation and improving thermal conductivity.Incoordination of electrothermal properties will reduce the matching degree between functional SR and the application scenarios.How to solve the contradiction of co regulation of electrothermal properties is a key problem in the design of SR materials.In order to solve the above problems,this paper makes comprehensive use of micro-simulation and experimental observation methods to carry out systematic research on the functional SR aided design method,the internal correlation mechanism of thermal conductivity and conduction path,as well as the cooperative control schemes of electrothermal properties,with a view to providing theoretical basis and technical support for the enhanced design of stress cone insulation for high-voltage cable accessories.A molecular model for SR composites with actual conformation was constructed by using the cross-linking relaxation alternative strategy.The calculation error of the model was less than 5%,laying a methodological foundation for subsequent filler selection.Based on nonequilibrium molecular dynamics and electron Boltzmann transport equations,molecular simulations were conducted for five candidate fillers,and key physical parameters such as thermal conductivity and electrical conductivity for the optimal selection of fillers were calculated.Using these physical parameters,a filler potential evaluation index with equivalent mathematical form to the Schottky effect description formula was proposed,and the optimization selection method of SR composite doped with inorganic filler was established,which can achieve targeted molecular simulation assisted design for performance regulation goals.Based on the optimization of fillers,the internal correlation mechanism between thermal conductivity and conduction path of functional SR was further studied.A multi-particle random distributed model of SiC/SR composite was established,which integrates the actual particle size distribution,and reduces the calculation error of the model.Based on the established model,the definition and ergodic calculation method of SiC particle contact probability in composites were proposed.The particle contact probability was used to quantitatively characterize the contribution ratio of the connecting particle phase and the discrete particle phase to the thermal conductivity,and a highly reliable model for predicting the thermal conductivity of SR composites was established,with an accuracy exceeding the existing model by more than 20%,providing theoretical guidance for the follow-up SR composites electrothermal coordinated control.As a regulation method based on the electrothermal conduction path,compound modification provides a pathway for phonons by improving the particle contact probability,and also promotes the electron migration.The experimental results show that the compound modification can effectively regulate the electrothermal properties of SR,and the thermal conductivity can easily meet the regulatory requirements,but there are still certain limitations in the regulation of electrical conductivity.In order to achieve the goal of coordinated regulation of nonlinear conductivity and thermal conductivity,we start with the differences between electrical and thermal conduction behavior,and constructs SiC micro-structure with high contact probability and high potential barrier by regulating the distribution characteristics of fillers.The distribution control scheme of micro/nano SiC based on electrostatic adsorption was proposed,and the preparation process of SiC self-assembled structures oriented to the control goal were determined,that is,system pH is set as 7.the adsorption temperature is set as 40℃-60℃,and the adsorption time is set as 2 h-3 h.Based on the normalization process and screening functions construction,a binary function evaluation index for the volume ratio and particle diameter ratio of micro/nano SiC structures was proposed,and an optimization method for SiC self-assembly patterns was established.The optimization and selection of SiC self-assembled structures is transformed into a mathematical problem for solving the maximum value of the evaluation function.The optimal SiC self-assembly structure is the volume ratio of nanometer to micrometer 1:10.and the particle size ratio 1:200,which realizes the coordinated regulation of the electrothermal properties of SR composites.The mechanism of the micro/nano coating structure formed by the self-assembly mode on the electrical and thermal properties of SR composites was clarified.The micro/nano coating structure formed by using SiC self-assembly mode improves the compatibility between filler and matrix,resulting in a 10%reduction in interfacial thermal resistance.Meanwhile,the constructed micro/nano contact surface increases the SiC contact probability by 24%.The combined effect of the above two factors further improves the thermal conductivity of the SR composites.The self-assembly mode changes the barrier structure at the micro/nano SiC interface,increasing the barrier height by 13.6%,limiting the carriers involved in the conductive process,and allowing the conductivity of the composite to enter the desired regulatory region.Using the self-assembled SiC/SR material designed in this paper as the field grading layer for cable terminals can reduce the local field strength in key areas by more than 60%.Simulations and sample testing results verify the effectiveness of the composite materials prepared. |
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