Study On The Aging Characteristics Of ±500kV Ge-Nan D.C. Composite Insulators Shed Materials

Good pollution flashover performance of composite insulation made it widely used in high voltage D.C transmission line.But,with the increasing of composite insulators usage,as same as the operation life longer,problems of material performance degradation emerged,which includes efflorescence,harden,brittle,crack,appear the mark,dendritic channels,erosion,hydrophobic drop,local heating and mechanical strength decreased of shed materials,and so on.The aging of composite insulators has been got serious attention in recent years.Ge-Nan D.C transmission line is the first D.C line of our country with typical representative significance.This paper has investigated the aging performance by using of the composite insulators which were taken out of service in 2009 from Ge-Na line.The testing methods including traditional testing means like appearance inspection,hydrophobic and suppleness inspection;Silicone rubber material performance test,such as hardness,flame resistance,tracking and erosion resistance.Moreover,some new methods such as dielectric spectrum,thermal simulated current testing have been adopted to evaluate the aging properties of composite insulators.According to the test results,the silicone rubber shed material of Ge-Nan D.C transmission line will appear a variety of changes(including the change of color,micro cracks,etc.)after the long time operation.It usually could be found the occurrence of white powder precipitation(pulverization)after surface flashover occurred,but this phenomena could be observed sometime even though no flashover.;It also could be found that all of the surface hydrophobic disappeared,or even unrecoverable;Hardness and tensile strength would be changed along with the service time,but due to the vulnerable to external factors,the above parameters would be influenced and it would influence the judgment of the aging state of composite insulators.However,the dielectric spectrum test results shows that it has good relationship with the long time aging state of composite insulators which corresponding to the increasing of dielectric loss value that caused by destroying of polymer internal structure,polymer degradation,the main chain fracture and emerge silicon and polar group.In addition,it was found that the space charge quantity obtained from the thermal stimulation current curve would be increased along with the deepening of silicone rubber material aging degree.Based on above results,it is relatively effective method to use the dielectric spectrum and thermal stimulation current for the evaluation of aging state of composite insulator shed material.