Research On Early Warning Of Power Supply Line Joint Failure In High Speed Railway

In recent years,with the rapid development of high-speed railway in China,27.5kV single-core cross-linked polyethylene insulated high-voltage cable for traction power supply has been widely used.However,the cable joint in the production and installation process is prone to the problem of insulation defects,its insulation is aging to breakdown under the action of long-term voltage,eventually cable joint failure comes out.In order to ensure the safe and reliable power supply of the cable line,the insulation status of the power cable joint should be mastered in time,and the problems existing in the cable joint should be discovered in advance,so as to avoid the accident of the cable joint failure.Therefore,it is very important to study the change of electrical characteristics in the process of cable joint insulation aging.The main content of the thesis is as follows:Firstly,the relationship between the electric-thermal-mechanical coupling field during the aging of cable joint insulation is analyzed,and the mathematical model of the electric-thermal-mechanical coupling field is established,including the control equation,the boundary condition setting,and the simulation flow between multiple physical fields.The numerical solution method of the electric-thermal-force coupling field of cable joints is determined.The emphasis is on the calculation of electric-thermal-mechanical characteristics of cable joints under the effect of insulation aging and the analysis of their laws under the influence of insulation aging and ambient temperature,and on this basis,determine the characteristic signal of insulation aging state,the characterization method and the criteria for insulation aging and breakdown.Then,according to the principle of ultrasonic wave generated by partial discharge of cable joint insulation,the relationship between electric-thermal-mechanical-acoustic coupling field when the cable joint insulation is discharged is analyzed,and the mathematical model of acoustic-solid coupling field is established.The numerical solution of electric-thermal-mechanical-acoustic coupling field of cable joint is determined.Emphasis is placed on analyzing the variation law of ultrasonic characteristics and the influence of frequency on sound pressure during the development of partial discharge of cable joints,and on this basis,determine the characteristic signal and characteristic quantity to distinguish the degree of cable joint insulation defects.Then,the calculation method of heat loss of cable joint connection parts is studied,and the simulation flow of thermal-mechanical coupling field of cable joint under pressure welding process defects is analyzed.The emphasis is on the calculation of thermal-mechanical characteristics of cable joint under the action of pressure welding process defects and the analysis of its rule under the influence of contact coefficient and contact pressure,and on this basis,the characterization method of cable joint pressure welding process defects is determined.Finally,according to the above research,the diagnosis method of cable joint fault is determined,and a scheme of cable joint fault early warning system is designed.