| With the rapid development of electrified railway toward high speed and heavy load,the electrified railway in China is faced with new challenges and problems.Direct power supply system with return cable and auto-transformer(AT)power supply system are the common power supply system of China.The above system includes multiple conductors such as contact cable,carrier cable and rail,which forms complex structure and relation of electromagnetic field.In order to accurately grasp the electrical characteristics of the traction network system and provide a precise theoretical basis for the safety problems of the electrified railway operation,it is necessary to realize the accurate mathematical description of electrified railway traction network and the precise extraction of electrical parameters,based on electromagnetic spatial theory.Starting from the fundamental spatial electromagnetic theory and regarding the railway traction network as complex multi-conductor transmission-line(MTL)system,this paper aims to realize the accurate modeling and electrical parameter calculation of traction network By studying new method of electrical parameter calculation,a loop method of MTL system is proposed.The implementation process of this method is illustrated according to the route of 'Study on the spatial electromagnetic description method of MTL system->Fundamental electrical parameter calculation of MTL system->Internal impedance analyses of irregular cross-section conductors in traction network'.The application researches of the loop method of MTL system and its verification are also made,respectively aimed at the traction network impedance of the subgrade path,the traction network impedance of the tunnel path,the integrated current-carrying capacity of traction network and the distributions of rail potentials and rail currents.The main work of this paper is listed as follows.1)Considering that the traditional analysis method of MTL system using the earth as a reference conductor is lack of completeness and accuracy,the loop method of MTL system that uses current loop circuit as the fundamental spatial electromagnetic description unit is proposed.This method not only considers all the conductors that are actually involved in the transmission and return of currents,but also taken into account the return of the earth current.Then,focusing on the different types of multi conductor loop system,the analyses of spatial magnetic field and the deduction of analytical calculation formula of unit-length integrated inductance are performed.The effectiveness of aforementioned analysis and deduction method is proved using MATLAB/Simulink software.Meanwhile,the situation that overhead return condition exists in traction network is also considered.And the influence of the earth on the loop circuit of overhead conductors is analyzed.That is,the impedance values calculated by overhead conductor loop method,simplified Carson formula and Dubanton formula are compared,And the results indicates that the influence is negligible.2)Focusing on the conductors with irregular cross section such as rail,contact conductor and integrated ground wire,the application of finite element method in the electrical parameter determination is studied.The analyses of the electrostatic fields and the eddy current fields are combined,and the accurate unit-length electrical parameters of these conductors are obtained.3)Considering the essential characteristics that traction network system is composed of many loop circuits,the loop method of MTL system is applied to perform the spatial magnetic field descriptions,respectively for the direct supplying traction network and the AT supplying traction network(including long loop circuit and segment loop circuit)of single track and double tracks with different operation modes on subgrade path.Meanwhile,the electrical structure of AT supplying traction network is combined,and the concept of constraint equations and the iterative method of approaching current distribution are proposed.By using the iterative method,the spatial description of magnetic field is corrected.Further,utilizing the incidence formula of spatial magnetic fields and electrical parameters,the unit-length impedance of traction network on subgrade path is calculated.4)Combined with the specific features of tunnel in electrified railway,the impedance parameters of traction network in the tunnel environment are studied in detail.Then,by using the calculation method of traction network impedance on subgrade path,the magnetic field spatial description is given to obtain the unit-length traction network impedance,respectively for the direct supplying traction network and the AT supplying traction network(including long loop circuit and segment loop circuit)of single track and double tracks with different operation modes on tunnel path.5)On the basis of thermodynamic equation,the formula of conductor's temperature rise and conductor's current-carrying capacity are deduced.And the current distribution of each loop circuit is obtained,combined with the loop method of MTL system.Aimed at the direct supplying traction network and the AT supplying traction network of single track and double tracks,the analysis and calculation on comprehensive current-carrying capacity are made.6)Based on the calculation results of spatial magnetic field analysis and loop circuit method of MTL system,a method of solving rail potential and rail current is proposed.The proposed method considers three sources of rail potential and rail current,including the source excitation generated by the currents that flow into rail and flow out of rail,the interfering incident field excitation caused by the inductive couple of currents of conductors other than rail and the earth and the capacitive couple of traction network loop circuit voltages,and the interfering incident field excitation caused by the inductive couple of other rail-earth loop circuits in the studied rail-earth loop circuit.By applying this method,rail potentials and rail currents of direct supplying traction network and AT supplying traction network are calculated7)Combined with the short-circuit experiments of multiple actual railway lines(line from Chongqing to lichuan,line from Chengdu to Chongqing,etc),the comparison with the calculation results of traditional methods,the study on the current distribution index of each reflux conductor in electrified railway traction network,measurement and simulation results of existing literatures and so on,the validity and accuracy of the proposed analysis and calcculation methods on the traction network impedance of the subgrade path,the traction network impedance of the tunnel path,the integrated current-carrying capacity of traction network and the distributions of rail potentials and rail currents are proved,respectively. |
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