| Stress control tubes(SCT)are used to relieve and improve vehicle high voltage cable terminals’ core part of the internal centralized electric field distribution,also an important part to ensure that the terminal has excellent insulation structure.Therefore,there are higher requirements for its design and installation in engineering.Due to those special operation conditions and installation positions,SCT are easily interfered by the continuous thermal stress from cable core and external environment temperature,resulting in the aging and modification of its material,defects,and the reduction of the stability of related electrical and mechanical properties,which eventually leads to the decline of the overall insulation performance of the terminal,and thus seriously threatens the operation safety of EMUs.For exploring those effects of long-term natural thermal aging on the electrical and mechanical properties of SCT,this paper follows the corresponding law between the artificial accelerated thermal aging rate and the natural aging rate of insulating materials,and designs the artificial accelerated thermal aging test scheme of SCT with reference to the relevant test standards,carries out these measurements and researches on the relevant characteristic parameters,and eventually verifies the degradation mechanism and evolution rules of electrical and mechanical properties of SCT samples under different aging conditions;.The main research work is as follows:Firstly,an artificial accelerated thermal aging test platform for SCT of vehicular high voltage cable terminals was built,and the change rules of dielectric constant,dielectric loss,volume resistivity and other electrical performance parameters of SCT samples under different aging conditions were studied in combination with the actual operation conditions and fault types of cable terminals;The influences of parameters changes on the electric field distribution of the whole cable terminals with the corresponding dielectric characteristics of SCT samples were verified with the aid of finite element simulation software.Secondly,the flashover test platform of composite interlayer interface model of cable terminals composed of aging SCT samples and EPDM was built,and the influences of SCT samples under different aging conditions on the discharge characteristics of composite interlayer interface model was verified,and the development process of discharge of composite interlayer interface of actual cable terminals was demonstrated.Combined with two parameters Weibull distribution,the parameters related to flashover voltage of the composite interlayer interface model were estimated,and the flashover resistance ability of the model under any electric field was determined by combining the fitting function relationship.Further more,the surface potential of SCT samples under different aging conditions was studied,the surface charge transport model was established,and the surface potential decay curve of the samples was drawn with supporting of MATLAB.The influence mechanism of the surface deep trap energy level center,peak density,carrier mobility and conductivity of SCT on the flashover characteristics of the interface between the composite layers was discussed.At last,a test platform for mechanical properties of SCT samples of vehicle mounted high voltage cable terminals was built.Through testing the tensile strength and elongation at break of SCT samples under different aging conditions,the critical point of material mechanical parameters aging failure was found out,and the degradation law of relevant mechanical properties was proved.With the aid of FTIR,SEM and other testing and analysis technologies,the different aging was studied from the micro level under the condition of degradation,the change rule of micro molecular groups and surface morphology of SCT samples,eventually those researches indirectly revealed the degradation and evolution rule of mechanical properties of SCT.The successful development of the above research and testing work could provide theoretical reference for the production,installation and evaluation of the overall insulation process of the terminal,which has certain engineering reference value and significance. |
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