Theoretical Analysis And Test Of Crosstalk Of Railway Signal Cables

With the development of economy,the demand for the speed and carrying capacity of railway transportation is increasing rapidly.Under the requirements of development,the electrified railway's traction power has also significantly increased.A variety of electronic equipment have been fully applied in the railway system.The electromagnetic environment of the railway signal equipment has become more and more complicated.Thus,the interferences between signal equipment are more frequent.There is an urgent need for relevant theoretical analysis,simulation and measurement of crosstalk between signal equipment,and finding out the effective measure to protect equipment from electromagnetic interference.In this paper,the theoretical analysis,mathematical models,simulation and measurement of the crosstalk between signal cables are carried out based on the current situation and the characteristics of the railway system in our country.The research objects include non-shielded cables,single shielded cables and double shielded cables.According to the complexity of the research objects,the coaxial and coplanar model,per-unit-length model and electromagnetic topology model are established,and respectively simulate and analyze the crosstalk using MATLAB software.The measurement system of the crosstalk is proposed based on the coaxial and coplanar model,which consists of a signal generator,a power amplifier,an oscilloscope,and a control software based on LabVIEW.The main contents of this paper include:(1)Appropriate model to analyze crosstalk between different types of cables.(2)The influence of locations(coaxial and coplanar)and media to the crosstalk of non-shielded cables.(3)The influence of signal circuit's grounding model(grounding or floating),the number of shielding layer(single or double)and the different combination of shield grounding model(double floating,single end grounding or double end grounding)to the crosstalk of the cables.According to the results of theoretical analysis,simulation and measurement,the effective measures to restrain the crosstalk between cables under different conditions are determined.The main conclusions of this paper include:(1)Crosstalk between coaxial cables is much stronger than that between coplanar cables.(2)Medium has little effect on the crosstalk of cables.(3)Grounding of signal circuit will introduce a grounding circuit,which increases the crosstalk between two circuits when frequency is low.(4)The shielding effect of double shielded cables is obviously stronger than single shield cables.(5)The shielding effect of shielding layer cannot be realized by floating,the grounding at one end can restrain the electric field coupling,and the grounding at two ends can restrain not only the coupling of electric field but also the coupling of magnetic field.(6)In terms of the double-shield cable,if the signal circuit is floating,the outer shield is grounded at two ends and the inner shield is grounded at one end,then the crosstalk between shield cables is the minimum.