Research On Lightning Electromagnetic Transient Model Of High-speed Railway On The Viaduct Section

In China,viaduct structure is widely used in the design and construction of high-speed railway,and viaduct section accounts for 54 percentage of total traffic mileage of high-speed railway.Compared with roadbed section,catenary in viaduct section is relatively higher.Scholars research the catenary in viaduct section with EGM and LPM.It has been found that lightning attraction scope of catenary in viaduct section is wider,and suffers much more threat from lightning strike.Lightning strike on catenary may cause operation faults of high-speed railway,which leads to train delay.It may threaten the security of train and passenger in severe case.However,the electromagnetic transient process in viaduct section is rather complicated because the existence of steel mesh structure,meanwhile the structure and geometric parameters of viaduct are different.This makes it very hard to achieve accurate electromagnetic transient model of viaduct.Therefore,the work deriving the electromagnetic transient model of high-speed railway in viaduct section,and conducting research of lightning characteristics base on the model is very significant to lightning protection for high-speed railway.Firstly,Spectrum of common lightning current is analyzed,and frequency range that should be concerned in lightning electromagnetic transient research is confirmed.Secondly,black-box principle is adapted,viaduct is considered as entirety and the bottom of catenary pillar is treated as port,then port impedance characteristic is studied,and the influence of structure and geometric parameters to impedance characteristics is analyzed.Thirdly,impedance function of viaduct is acquired with vector fitting method,and passive port equivalent circuit of viaduct impedance function is derived according to electrical network theory.Equivalence of circuit under impulse condition is verified by choosing different lightning waveform.Fourthly,the discrepancy of different insulator flashover criterion is analyzed,and lightning electromagnetic transient model of high-speed railway in viaduct section is established.At last,the influence of lightning strike point,grounding resistance and viaduct height to catenary lightning withstand level is researched with the model established above.By analysis of lightning current spectrum,it found that calculation frequency range should higher than 5MHz while making electromagnetic transient research.Geometric construction makes much difference to viaduct impedance,the peak number,amplitude and interval of impedance curve is various for different viaduct.First peak is higher than the following peak,and first peak always appears in 0?5MHz.It proved that the circuit can is equivalent to viaduct under impulse condition.It found that the insulator model using definition method criterion is not proper,as the voltage waveform of insulator might be short tail wave in actual operation.In the following research,it found that the insulator model using LPM criterion accord with physical process.Lightning withstand level of catenary in viaduct section is calculated under two typical waveform lightning,it found that shielding failure lightning withstand level is little,only-3.2 to-3.4kA,and grounding resistance and viaduct basically makes no effect to the shielding failure lightning withstand level.The strike-back lightning withstand level decreases with the increase of grounding resistance and pier height.The strike-back lightning withstand level under short wave-front time lightning is much lower than that under long wave-front time lightning case.With simulation calculation and contrast research,it confirmed that the electromagnetic transient model of high-speed railway in viaduct section established in the paper is accord to the physical reality,and the model can be adapted in lightning characteristics analysis for the high-speed railway in viaduct section.The research result can provides reference to the calculation of catenary lightning withstand level of high-speed railway in viaduct section and the research of electromagnetic transient model.