Defects Evolution Process And Mechanism Of Discharge Embrittlement Of GIL Post Insulator Inserts And Epoxy Interface

Gas insulated transmission lines(GIL)have the advantages of high ampacity,high reliability and small transmission loss,and have become one of the important solutions to solve long-distance large-capacity power transmission projects such as cross-river and cross-sea,and insulation failure is always one of the important reasons affecting the stable operation of GIL.In this paper,it is considered that the evolution of pillar insulator insert-epoxy interface defects is closely related to explosion,so it is of great significance to clarify the evolution process of GIL pillar insulator insert-epoxy interface defects,explain the explosion mechanism,and finally propose an insertepoxy interface insulation reinforcement design method,which is of great significance to improve the insulation performance of GIL insulators.The main research work and research results obtained in this paper are as follows:In order to study the typical characteristics and key influencing factors of pillar insulator explosion,a pillar insulator with air gap defect was designed and a pillar insulator explosion simulation experimental platform was built under the action of electrical-thermal-mechanical coupling stress,and the evolution and explosion process of insulator insert-epoxy interface defects were studied.Based on the experimental results,the explosion process of pillar insulator is divided into three characteristic stages:crack generation and propagation stage,fracture stage,explosion stage,partial discharge caused by air gap defect will induce crack generation and deterioration propagation,resulting in rapid fracture of the insulator in a very short time and explosion under multiple high-energy arc impacts,showing the characteristics of brittle fracture.At the same time,the key factors affecting the explosion of pillar insulators are analyzed experimentally,and the explosion probability of insulators under DC voltage is 10-20%lower than that of AC voltage.Finally,the interaction between surface metal foreign matter and interface defects was analyzed experimentally,and when the metal foreign matter was adsorbed in the middle of the insulator,the explosion probability of the pillar insulator increased the most,increasing to 20%.In order to study the bursting mechanism of pillar insulators,this paper further constructs a crack propagation phase field simulation model under electro-mechanical coupling,and analyzes the dominant mechanism of different bursting stages of pillar insulators.In the stage of crack generation and propagation,electric potential energy plays a major role;In the fracture stage,the role of electric potential energy gradually weakens,the mechanical potential energy gradually increases and plays a leading role,when the mechanical potential energy reaches the critical point of material stress,the insulator bursts brittlely.In addition,the influence of the stress in the insulator on its crack propagation is revealed,and when the microbubble appears near the evolved crack,the energy fluctuation of the crack tip evolution can be transmitted to the bubble,resulting in microcracks around the bubble,which causes the scope and number of cracks to continue to expand,and eventually leads to the explosion of the insulator.On this basis,the interaction mechanism between surface metal foreign matter and insertepoxy interface defects was analyzed.An insulator insert-epoxy interface insulation reinforcement design method is proposed.Based on the nonlinear conductivity coating,an epoxy resin coating with SiC as the main filler was designed and manufactured,and it was found that the epoxy resin coating with 40%SiC content could effectively reduce the explosion probability of the pillar insulator,and to a certain extent,the degree of bonding between the epoxy resin and the insert was improved.In summary,metal insert-epoxy interface defects will have a serious impact on insulation performance,which is an important cause of insulation failure in the longterm operation of GIL.The research content of this paper is of great significance for improving the reliability of GIL in long-term service,and can provide an important basis for subsequent in-depth research.