XLPE Cable Intermediate Connector Research On Dielectric Properties And Aging Characteristics

Power cable is the carrier of energy transmission in the power system,and the reliability of its cable accessories has always been the core element of the safe operation of cable lines.However,with the increase of operating years,cable joints are prone to deterioration and failure of insulation performance,resulting in power cable operation failures.Silicone rubber is the main insulation material of the cross-linked polyethylene cable intermediate joint.The physical and chemical properties and electrical properties of the silicone rubber material are the key to the stable operation of the cable intermediate joint.The dielectric properties and physical and chemical properties of silicone rubber insulation of joints with different service years were studied,the corresponding changes of the physical and chemical properties of silicone rubber and insulation degradation were revealed,and the mechanism of insulation degradation was analyzed.Infrared spectroscopy was used to characterize the changes in the chemical composition of the silicone rubber material.It was found that with the increase in service life,the infrared absorption peak area of the main chain structure of the silicone rubber sample continued to decline,indicating that aging occurred,but the width of the vibration peak was not obvious.No serious deterioration of the insulation material;through the density test,it can be found that the density of the silicone rubber sample shows a downward trend with service time,which may be related to the electric heating effect after the cable joint is put in;the thermal weight loss analysis is used to study the heat of the silicone rubber insulation Stability,it was found that the initial decomposition temperature,residual carbon content and other parameters of the running sample were reduced to varying degrees compared to the non-running sample,indicating that the silicone rubber after operation was affected by thermal aging and the thermal stability decreased.The physical and mechanical properties of the four samples were tested,and the results showed that the tensile properties of the running samples showed a downward trend compared with the non-running samples,but the elongation at break of samples with short service life increased instead.This may be related to the thermal rearrangement effect at high temperature and high field strength.After service,the elongation of the silicone rubber sample under load increased to varying degrees,indicating that the degree of crosslinking decreased.It can be seen from the dynamic thermomechanical analysis that the storage modulus of the silicone rubber insulation put into operation is reduced,indicating that the general elastic deformation caused by the change of the molecular segment causes the silicone rubber to decrease in rigidity and increase in flexibility.The volume resistivity,breakdown field strength,dielectric constant and dielectric loss tangent of the silicone rubber material were tested,and the activation energy calculation was performed based on the volume resistivity test results.It was found that the unactivated samples had the highest activation energy and interface barrier.After putting into operation,the carrier concentration of the sample increases,and the activation energy decreases.The breakdown field strength results show that the breakdown field strength of the sample after operation shows a downward trend with service time,which is related to the distortion electric field formed after the sample ages.The broad-band dielectric spectrum curve shows that the thermal insulation of the silicone rubber insulating molecular chain structure undergoes thermal degradation,and the main chain is broken to undergo a depolymerization reaction.This process destroys the main chain symmetry of the silicone rubber,resulting in an increase in dielectric constant.As the temperature increases,the dielectric constant and dielectric loss of the silicone rubber sample change significantly in the low frequency band,which shows that the dielectric constant decreases and the dielectric loss increases.