Temperature Differential-based Characterization Method For The Location And Depth Of Internal Defects In Vehicle Cable Terminals

As an important hub for energy transmission of high-speed trains,the service status of vehicle cable terminals will directly affect the safe operation of trains.Affected by the construction process,car body vibration,sudden changes in ambient temperature and other factors,the insulation defects between the layers of the vehicle cable terminal are very easy to produce,thus affecting its normal service.Therefore,timely and accurate location detection of the internal defects of the on-board cable terminal can effectively avoid the occurrence of faults.In view of the poor anti-interference ability of the partial discharge detection method and the susceptibility of the temperature detection method to environmental temperature changes,this paper proposes a temperature differential method to provide a new way of thinking for the characterization and detection of internal defects in vehicle cable terminals.The paper completed the theoretical derivation of the analytical solution of the multiorder function of the surface temperature of the vehicle cable terminal under the action of the heat source of internal defects,constructed the analytical relationship between the differential parameters of the surface temperature and the location of defects,built an experimental platform to verify the differential method,established a finite element simulation model of the electric-thermal coupling of the vehicle cable terminal containing defects,and further verified the feasibility of the proposed method in the localization and detection of internal defects.The main work is as follows:(1)A differential model of the temperature field of the vehicle cable terminal under the action of internal thermal defects is constructed.Firstly,based on the operation state,structural composition,material parameters and Fourier’s law of the vehicle cable terminal,the thermal equivalence analysis method is studied,which simplifies and equates the multi-layer composite structure of the vehicle cable terminal into a single-layer columnar structure and the internal defects to an internal heat source.Secondly,based on the equivalent single-layer model of the vehicle cable terminal and the solid heat conduction law,the surface temperature distribution,tangential temperature distribution and its second-order,fourth-order and sixthorder derivative under the action of internal defective heat sources are analyzed.The surface temperature distribution,tangential temperature distribution and their second-,fourth-and sixth-order derivatives under the action of internal defect heat source are analyzed.(2)A temperature differential characterization method for the location and depth of internal thermal defects is proposed.Firstly,based on the differential model of temperature field,the characteristics of surface two-dimensional temperature and one-dimensional curve temperature differential distribution are analyzed,and obtained that the surface twodimensional temperature differential distribution has the main peak feature and the onedimensional curve temperature differential distribution has the main side peak feature.Secondly,the relationship between the location and depth of thermal defects and the differential characteristic parameters is analyzed,and the analytical formula shows that the location of the main peak of the two-dimensional temperature differential distribution and the one-dimensional curve differential distribution is the location of thermal defects,and the distance of the main side peak of the one-dimensional curve temperature differential distribution can calculate the depth of thermal defects.Thirdly,a heat transfer model with multiple thermal defects was established to investigate the influence of defect depth and size on the differential distribution of the temperature field,and it was found that the larger the defect depth and smaller the size,the smaller the error of the temperature differential method.Finally,an experimental platform was built to verify by experimental means that the temperature differentiation method can detect the location and depth of internal thermal defects.(3)The simulation calculation of temperature differential method of vehicle cable terminal with internal defects is completed.Firstly,according to the electric-thermal field coupling theory and mathematical equations,the electric-thermal field finite element simulation model of the vehicle cable terminal under normal operating conditions and air gap defects is established,and the simulation results show that the existence of air gap defects increases the surface temperature.Secondly,the surface temperature distribution and tangent temperature distribution of cable terminals under the action of air gap defects are extracted,and the error of air gap defect depth calculated by using surface temperature differentiation method is within 10%,which further verifies the feasibility of the proposed method in characterizing the location and depth of the internal defects of the vehicle cable terminals.