Resarch On Lighting Fractal Propagation Conforming To Existence Of Catenary System Of High-speed Railway With Viaduct Based On Numerical Method

High speed railway plays a protagonist to overcome traffic congestion due to the advantages,such as strong transportation capacity and rapid transportation,meeting the modern economic requirements in China,a country with large population.The vast territory of China results in diversity of climates and regions which is one of primary causes to make a decision to employ viaduct application design.Eventually,the power supply system of high-speed railway is suffered from lightning stroke more easily because of employment of viaduct mentioned before.Therefore,to work on lightning protection research,which is according with Chinese high-speed railway conditions,is a significant task for China.According to real situations of power supply system of Chinese high-speed railway,this paper systematically studies lightning fractal propagation mechanism and associated lightning stroke performance when lightning stroke occurs on power supply system or in regions near the viaduct,based on numerical analysis theory and fractal theory.In this paper,a related lightning fractal model is established based on the fractal theory,finite difference method and overrelaxation iterative method.The simulation results of this model are compared with the existing research results aiming to verify correctness of the model.In further study of the model,It could be concluded that the upward leader incepts difficultly form catenary system before the last jump from lightning downward leader to stroke object.The results not only confirm the obvious difference from high speed railway catenary system with viaduct to the both EHV and UHV transmission power systems.It shows that the upward leader incepting from catenary system does not affect the final lightning stroke point and the result means the model can be simplified as a unconsidered upward leader model which is the basic model used in later research.Based on the simplified model,this paper studied the space electric field distribution,lightning stroke rate distribution and lightning attraction scope distribution related to each condition of the four conditions mentioned above.The former two and the latter are respectively carried on by changing schedule and parameters of basic model,and combining with two numerical analysis theory that are the least squares polynomial curve fitting algorithm and the Newton iteration method.The research results of space electric field are shown: Compared results with working voltage condition to results without working voltage condition,the distribution of space electric field is more symmetric and the distribution of the strong field part is more concentrated;the higher the height of the viaduct,the greater the distortion degree of space electric field in the vicinity of viaduct;The magnitude of space electric field is increased with the increment of lightning current amplitude,and the distribution of electric field in the space——the height of which is lower than the height of last jump happening——is more uniform at the moment before the breakdown.The research results of lightning distribution stroke rate are shown: with or without working voltage on both the AF and T wires has a weak effect on lightning stroke rate;the lightning stroke rate is increasing to the maximal,but the velocity of the rate increment is increasingly reducing with the increment of the height of viaduct and lightning current amplitude;curve of lightning stroke rate distribution related to horizontal distance between inception position of downward leader and viaduct has a symmetrical distribution around perpendicular bisector of bridge floor in which the farther horizontal distance,the lower lightning stroke rate;if the horizontal distance mentioned above is larger than 70 m,the lightning attraction capability of catenary system depends on left AF wire or right AF wire respectively;with each of four conditions mentioned above,AF wire could protect T and PW wire from lightning stroke.The research results of lightning attraction scope distribution are shown: lightning attraction scope with working voltage on both the AF and T line is slightly larger than the one without working voltage;the lightning attraction scope is increasing with increment of height of viaduct the lightning attraction scope is increasing firstly then decreasing with increment of amplitude of lightning current until rising up to a constant value.