Some Theoretical Studies On Pantograph-catenary Arc Electromagnetic Interference Propagation

Laboratory test results show that Electro-Magnetic interference of pantograph-catenary arcing, which has a wide frequency specturm, is a powerful interference source. On the one hand, the conductors of traction power:catenary, feeder, rails and so on, constitute the multi-conductor transmission line (MTL). Therefore, the EMI of pantograph-catenary arcing can propagate along the MTL. On the other hand, the electromagnetic wave radiated by the EMI signals through the MTL can affect the normal operation of sensitive electronic equipments along the railway line. All the MTLs are set up above the lossy earth. Due to the long-term deposition, the lossy earth, which composed of a solid particles, water and air, shows obviously characteristics of multi-layer. Because of the trapped surface wave existed in the surface of hierachy, the propagation of EMI signals along the MTLs has undergone a significant change. In order to simplify the analysis, the earth is modelled as two-layer structure, and the lower layer is infinite. This thesis gives an investigation of the influence of auto-transformer, track circuit. Also analysis the propagation characteristic of EMI signals in the two-layer earth structure, which produced by pantograph-catenary arcing.This thesis presents the propagation characteristic of pantograph-catenary arcing EMI, based on Finite-Difference Time-Domain (FDTD) method of MTL. Firstly, the overhead MTL are equivalent to three or four conductors according to the different research objects. The self and mutual impedance matrix of two-layer soil are calculated, which is approximated by vector matching. Secondly, considering the influence to the electromagnetic wave propagation of EMI signals by the AT transformer and track circuit equipment, the steps to obtain the equivalent circuit is presented. Moreover, according to the state equation and output equation of the equivalent circuits, the FDTD iterative equation of the lumped element connected the MTL terminal and intermediate is deduced. From the results, we can see that the iterative formula is no longer a diagonal matrix, because the auto-transformer and the track circuit equipment is not connected between the the active line and the reference line.Based on the FDTD iterative formula, the trapezoidal voltage wave as the mathematical model of the pantograph-catenary arc electromagnetic interference sources is adopted. By adjusting the rise and fall times of the trapezoidal, the bandwith of EMI can be tuned. Therefore, the propagation characteristic of EMI with different bandwidth of soure can be analysised. The ground impedance of two-layer earth can affect the propagation characteristic of EMI, and thus, this thesis also disscuss the influence of different depth of two-layered earth on the propagation characteristic. Meanwhile, the propagation characteristic v.s. the distance between the arcing point and the auto-transformer and the number of AT are also analysised.Finally, the thesis studies the influence of the two-layer earth structure on the propagation charecteristic of EMI. Based on the frequency-domain Maxwell equation, the integral formula of infinitely long wire above the two-layer earth is derived. According to the contour integral theory, the total field in the surface of earth consists of direct wave, reflected wave, lateral wave and trapped surface wave. It is noted that the trapped surface wave is determined by the pole residue of the integrand. Meanwhile, it is demonstrated that the amplitude of trapped surface wave decay rapidly when leaving the ground. Based on the analysis of this thesis, it concluded that when the antenna above the earth1-3meters, the trapped surface wave can be neglected. Therefore, the testing standard of Railway applications-EMC could not show propagation charactersitc of the trapped surface wave. Meanwhile, the analysis results show the test results are not enough when the sensitive electronic equipment is close to the earth. An importamt additional test of electromagnetic interference close to the earth is essential.