Study On Nonlinear Dielectric Properties And Improvement Of Electric Field Distribution Of ZnO/EPDM Composites

As one of the key high-voltage equipment of high-speed train,the health status of onboard high-voltage cable directly affects the safety and reliability of high-speed train.As an important component of the vehicle cable,the cable terminal is faced with a very complex insulation structure and frequent overvoltage impact in the severe operating environment,which leads to partial discharge(PD)in the interlayer electric field distortion of the cable terminal,which often leads to safety risks.Because of the universality and potential harmfulness of the electric field distortion in the cable terminal,in order to solve this problem,this paper focuses on the nonlinear dielectric composites to improve the electric field distribution of the vehicle terminal and ease the local high electric field intensity.Using Zn O/EPDM nonlinear dielectric composite material as the stress control layer of the cable terminal,the dielectric constant of the stress control layer changes automatically with the change of the field strength when the overvoltage occurs Thus,it has important theoretical significance and engineering value to improve the internal electric field distribution of the cable terminal and improve the safety and reliability of the long-term operation of the vehicle cable terminal.This paper first introduces two kinds of cable terminals in active service in high-speed trains: prefabricated cable terminals and multi-layer heat-shrinkable cable terminals.At the same time,the finite element simulation model is established based on the geometric structure and material of the actual cable terminal.The electric field distortion of two kinds of cable terminals and the target dielectric properties of the materials needed to improve the electric field distribution stress control layer are obtained.Then the preparation platform of Zn O/EPDM nonlinear dielectric composites is built.Composites with different nonlinear dielectric properties were prepared by changing the size and concentration of doped Zn O ceramic particles.The prepared materials were characterized and tested,and the mechanism of nonlinear dielectric characteristics of the materials was explained.Finally,the effectiveness of nonlinear dielectric composites for electric field regulation is verified based on simulation and experiments.The materials that meet the requirements of the target dielectric properties are fitted and brought into the simulation model calculation.The results show that for prefabricated cable terminals and heat-shrinkable cable terminals,when nonlinear dielectric composites are used in the stress control layer,the internal electric field distortion is obviously improved.the larger the nonlinear coefficient β of the material,the better the effect of alleviating the local high electric field strength.At the same time,a test platform for needleplate gap corona discharge was built to study the inhibitory effect of different nonlinear dielectric materials on needle-plate gap corona discharge.The results show that compared with the materials with fixed dielectric constant,the nonlinear dielectric composites can effectively alleviate the electric field concentration in the extremely non-uniform electric field and weaken the intensity of the corona discharge in the needle-plate gap.The voltage required in each stage of the development of corona discharge is increased.And the larger the nonlinear coefficient of the material is,the more obvious the effect is.