Study On The Decay-like Degradation Mechanism Of Epoxy Resin In The Core Rod Of Composite Insulator

Silicon rubber composite insulator is favored by power system because of its excellent anti pollution flashover performance.Among them,the core rod is an important structural component to bear the mechanical load of composite insulator.In recent years,there have been a number of composite insulator decay-like fracture faults characterized by resin degradation and irregular fracture morphology,which seriously threaten the safety and stability of power system.At present,the research of composite insulator's decay-like fracture is still in the initial stage at home and abroad,and there is no clear conclusion on the causes of its fracture,influencing factors and other important scientific and technical issues,and there is no unified understanding of the mechanism of decay-like fracture.In view of the above problems,this paper has carried out single factor heat and acid aging tests and multi factor electric erosion aging tests on the epoxy resin samples of the core rod.By analyzing the micro morphology,epoxy resin content,characteristic groups and characteristic elements of the samples,the degradation mechanism of the epoxy resin of the core rod by the electrochemical reaction process under the synergistic action of single factor and multi factor of electricity,heat and acid is summarized.Through the failure analysis and material analysis of the actual crisp/broken edge core rod on site,the decay-like fracture characteristics in actual operation are obtained,and the feasibility of laboratory simulation of crisp aging and the correctness of degradation mechanism of epoxy resin under various factors are verified.The main conclusions are as follows(1)Thermal effect is one of the factors that cause the degradation of epoxy resin The thermal decomposition of the epoxy resin satisfies the Arrhenius equation,that is,the reaction rate is directly proportional to the temperature,resulting in the inverse ratio of the bending strength of the core rod to the temperature.At the same time,the degradation of epoxy resin is also related to the heating time.When the temperature is low but the heating time is long,the content of epoxy resin will be reduced and the mechanical properties will be reduced.The interface between glass fiber and epoxy resin is a weak point,where the epoxy resin will take the lead in decomposition.Glass fiber lost the protection and bonding of epoxy resin,and became fluffy and even fractured under the impact of gas products and thermal stress.Acid corrosion is one of the factors that cause the degradation of epoxy resin.With the increase of nitric acid concentration and soaking time,the degradation rate of epoxy resin is accelerated,and the core rod sample gradually changes from emerald green to yellow brown,then to light yellow,and finally to white hairy glass fiber.The effect of the sample under the action of low concentration nitric acid for a long time is the same as that under the action of high concentration nitric acid for a short time.Nitric acid will continue to erode into the core rod,resulting in the decrease of hardness and performance on the surface of the core.The effect of nitric acid on epoxy resin is mainly corrosion dissolution,and the fiber has not been broken due to thermal stress.(2)In the heat and acid aging test,the heat energy and strong oxidizing nitrate:ions will attack the core epoxy resin matrix,resulting in the main chain(C-O-C,C-C)fracture,methyl(-CH3),aromatic(benzene ring)structure reduction,and the polymer macromolecules of epoxy resin gradually degradation.The ester group is hydrolyzed in acid environment to form carboxylic acid(-COOH)and alcohol.The silane coupling agent and the anhydride curing agent decompose and the crosslinking network is destroyed.With the gradual degradation of epoxy resin on the surface and the exposure of glass fiber,the content of C element on the surface of the sample decreased,and the content of O,Si and Ca element increased.The process of electric erosion includes thermal effect and acid erosion,the degradation mechanism of epoxy resin is as follows:In the discharge environment,the main chain of epoxy resin matrix breaks,the structure of methyl and benzene ring decreases,polymer macromolecules decompose gradually,and finally degrade into CO2 and H2O;In humid environment,the ester groups of coupling agent and curing agent in epoxy resin hydrolyze,the crosslinking network of epoxy resin is destroyed,and the epoxy resin is powdered;In the presence of water,strong oxidizing nitrate ions(NO3-)and amino compounds are formed by discharge,which further oxidizes the epoxy resin;The metal ions in the three-dimensional skeleton of glass fiber are replaced by H+,which causes the fiber to break.The nitric acid and amino compounds were Only detected in the samples under humid environment,which proved that the water intervention was the necessary condition for the formation of acid(3)The epoxy resin content of the crisp and broken core rod in the field was greatly reduced.By comparing the SEM images,TGA thermogravimetry curves and FTIR spectra of the field samples and the laboratory samples,it is considered that the laboratory samples reproduce the decay-like aging to some extent.The changes of the micro morphology,epoxy resin content and characteristic group content at different wave numbers are consistent with the field,which better proves the equivalence of single factor and multi factor aging tests and the correctness of the degradation mechanism of epoxy resin.