| Space launch sites are mostly built in sparsely populated open areas with launch towers up to 90 m high,especially synchronous orbit launch sites close to the equator,where lightning and lightning activities are frequent and vulnerable to direct lightning strikes.The current direct lightning protection system in the launch site can effectively shield the rocket launch tower,but there are still accidents caused by the indirect effect of lightning at home and abroad.The transient electromagnetic field of lightning will cause the abnormal operation of equipment and even cause the fault through space coupling.Therefore,the modeling and analysis of the transient characteristics of the lightning protection system and the electromagnetic transient characteristics in the near area of the lightning strike at the launch site will help to improve the lightning protection level of the rocket launch site,and also provide reference for the lightning protection design of the launching position of the missile body.Focusing on the analysis and protection of the lightning transient characteristics of the direct lightning protection system at the launching site,this paper mainly carries out three aspects of research work,including modeling and analysis of the electromagnetic transient characteristics of the direct lightning protection system,analysis of the electromagnetic transient characteristics of the near area of the lightning strike of the launching tower and analysis of the optimization design of the lightning protection scheme.The specific contents are as follows: 1)Based on the method of moments,a three-dimensional electromagnetic transient model of the direct lightning protection system at the launching site considering the structure of both underground and aboveground conductors is established,and a circuit model of the direct lightning protection system is established based on the theory of wave impedance,which verifies the validity of the three-dimensional electromagnetic transient model.2)The transient characteristics of the protection umbrella scheme,the lightning-tower without down wire scheme and the lightning-tower with down wire scheme are analyzed by the three-dimensional electromagnetic transient model,as well as the transient characteristics of the lightning strike near the area.The transient characteristics of the direct lightning protection system and the electromagnetic transient characteristics in the near area of lightning strike are studied,including the number of ground wires,soil resistivity,ground grid area,lightning tower layout,lightning strike position,lightning current waveform and so on.3)Considering the transient characteristics of the direct lightning protection system and the electromagnetic environment in the near area of lightning strike in the launching site comprehensively,the scheme of adding independent grounding and drainage system,adding insulation protection and optimization of grounding system is proposed to optimize the lightning protection scheme of the launching site,and the recommended comprehensive protection optimization scheme is given.The results show that: 1)in the study of transient characteristics of direct lightning protection system,it is found that the number of ground wire,the layout of lightning tower,the position of lightning strike and the lightning current waveform have a great influence on the potential rise at the top of the four lightning protection towers and the uniformity of the current flowing through the lightning tower,while the soil resistivity and the area of grounding grid have a small influence.2)In the study of electromagnetic transient characteristics in the near area of lightning strike,it is found that the number of ground wires,the layout of lightning tower and the lightning current waveform have a greater influence on the electromagnetic field at the observation surface,while the soil resistivity,the area of grounding grid and the location of lightning strike have a smaller influence.3)The optimization scheme of lightning protection is put forward by adding independent grounding drainage system and grounding network encryption of lightning tower.This scheme plays a good role in pressure and current sharing,and the transient magnetic field in the area where the transmitting tower is located is small.When the lightning current is200 k A,the ground magnetic field in the core area of the launching tower is the minimum with the amplitude of 78A/m(0.9Gs),which is far less than the critical magnetic field(2.4Gs)for permanent damage of electronic equipment.The maximum value of ground magnetic field appears near the lightning arrester nearest to the lightning strike point,and its amplitude is 576A/m(7.3Gs),which is higher than the critical magnetic field for permanent damage of electronic equipment.Therefore,it is suggested that electronic equipment should not be arranged near the lightning arrester as far as possible.The research results in this paper can provide reference for the design of lightning protection system of rocket launch site and the design of strong electromagnetic pulse protection performance of missile body. |
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