Study On Nondestructive Detection Methods For Aging Characteristics Of Silicone Rubber Materials

Compared with other regions in China,southwest China is always in high humidity,which leads to frequent corona discharge at the end-fitted metallic of composite insulator.Due to the corona discharge and high humidity,the silicon rubber material of composite insulator tends to be aging.It can weaken insulating properties,and even cause flashover accidents.Therefore,it is significant to test the performance of composite insulators and assessing their ageing condition.Traditional detection methods require strict laboratory environment and sophisticated and expensive measuring instruments and they cannot achieve non-destructive aging detection for insulators in operation.To solve this problem,this paper adopts two non-destructive testing methods to detecting the corona aging state of silicone rubber materials:nuclear magnetic resonance method（NMR）and image-processing-based droplet area method.In this research,silicone rubber samples with relative humidity of 40%,60%,80%,and95% are prepared under laboratory conditions.They are tested respectively by the non-destructive testing method and the traditional aging state testing method（FTIR,static contact angle）.After comparing the test results,the accuracy and reliability of the non-destructive testing method in this paper are verified.Meanwhile,the corona aging conditions of the silicone rubber material with different humidity are obtained.The results include:（1）The NMR method can effectively detect the changes of Si-CH₃ groups in silicone rubber materials’ molecular side chain before and after corona aging.The degree of aging can be indicated byΔT_2eff,the decrease of the equivalent transverse relaxation time.In contrast to the FTIR test results,the NMR method can accurately and clearly reflect the corona aging state of the silicone rubber.（2）The adaptive smoothing filter algorithm and the adaptive contrast enhancement algorithm are used in droplet area method to improve the Grab Cut algorithm.With this method,the hydrophobicity of clean samples,naturally contaminated samples,clean samples with different hydrophobicity,and corona aging samples are obtained.The results have verified the validity and reliability of the algorithm in this paper.The algorithm of droplet area method can test the droplet area changes before and after the aging process.（3）With the increase of the ambient humidity,the decrease amplitude in the equivalent transverse relaxation timeΔT_2eff gradually increases,and the droplet area on the surface of the sample also increases.This indicates that corona discharge in high humidity environment causes more serious damage to the nonpolar group-CH₃ of silicone rubber molecular structure,and also intensifies the loss of hydrophobicity of silicone rubber material surface.The non-destructive testing method can effectively detect the aging state of the silicone rubber material from both micro and macro perspectives,which guarantees the aging state of insulator is accurately judged in all directions.Meantime,portable equipment and simple operation applied in the non-destructive testing method meet the demands for on-site testing of composite insulators in complicated operating environments.