Thermal Aging Characteristics Of Semicon Materials For Cable And Accessory

The Polymer-based semicon material is often used in cable body and cable accessories to uniform electric field distribution and restrict partial discharge,so as to ensure long-term stability of power cable.The Polymer-based semicon material is a kind of filled conductive polymer.Physical blending method is usually used to product composite materials by adding conductive components into polymer insulate materials.The comprehensive properties of semicon material is not only related to the preparation process,but also affected by other factors.The direct current(DC)volume resistivity of semicon shielding material is used as the evaluation index both in national and abroad standard.However,it is not applicable to the actual operating condition that the cable operating under power frequency voltage for a long time and may withstand lightning overvoltage.The physical and chemical properties of the semicon shielding layer of the cable will be changed by aging during the long period of use.At present,the research on semicon material for cable and accessory is mainly focused on the development of initial properties and material formulations,but the research on the thermal aging dielectric properties of the semicon material is still rare.In this paper,Ethylene-Vinyl Acetate Copolymer(EVA)based shielding materials for cable body and silicone rubber based semicon materials for cable accessories are taken as the research object.The mechanical properties and dielectric properties of two kinds of materials before and during aging were tested,and the simulation model of cable accessory connectors was established based on the experimental data.The effect of aging of semicon materials on electric field distribution of cable connector is analyzed by simulation.The results of mechanical properties test of semicone materials show that after aging,the tensile strength of EVA based semicon materials increases than that of before aging,and the elongation at break decrease.The mechanical properties testresults of silicone rubber based semicon materials are so scattered that the effect of aging time and stress on the mechanical properties of silicone rubber based semicon materials are not obvious.The test results of dielectric properties of semicon materials show that the DC resistivity of EVA based semicon materials decreases first and then increases with aging time,and the DC resistivity of silicone rubber based semicon materials increases significantly with the prolongation of aging time.Both of the dielectric constant and the mode of complex dielectric constant of EVA based semicon material increased with the prolongation of aging time;the dielectric constant of silicone rubber based semicon material increased with the prolongation of aging time and the mode of complex dielectric constant decreased with the prolongation of aging time.In the early stage of aging,the loss factor of EVA based semicon material increased with the prolongation of aging time,and then decreased with the prolongation of aging time.The loss factor of silicone rubber based semicon material decreases with the prolongation of aging time.The electric field simulation results show that the maximum electric field strength inside the stress cone increases gradually with the decrease of the conductivity of semicon stress cone under DC steady state.