Application Of Electromagnetic Field Equation Of Moving Charges For Calculation Of Lightning Electromagnetic Pulse

Due to the sharp change of current pulse during the lightning discharge,a strong electromagnetic pulse will be generated around the channel.The detailed analysis and accurate calculation of the electromagnetic pulse have important practical significance for lightning protection and lightning location.The formation and transmission of current pulses are essentially the result of charge movement,so the current pulses can be regarded as moving charges.It should be noted that the charge moving in the channel described in the paper is the macroscopic equivalent motion charge,not the real charge.Based on the radiated electromagnetic field equation of moving charged particles,the lightning electromagnetic field can be calculated by analyzing the motion state of charge in the discharge channel.Based on the moving charge field equation and dipole method,the electromagnetic fields of CP and CG return stroke models are calculated respectively.In the CP model,the return stroke is the upward transmission of the current pulses originating from the ground along the channel.At the bottom of the channel,the accelerated radiation field will be generated when the moving charge accelerates from stationary to return velocity,and the velocity field will be generated when the charge moves uniformly along the channel.The return current in CG model consists of corona current released by channel element.There is no velocity field,because the corona current is transmitted at the speed of light.The result shows that although the electromagnetic field components obtained by the two methods are different,the total electromagnetic field is basically the same.The method can also be used to calculate and analyze the electromagnetic field of the model for lightning strikes to tall towers,which is the extension of the return stroke model.When the lightning strikes the tower,the charge moves differently in the tower and the lightning channel.The charge in the tower reflects back and forth between the top and the bottom of the tower at the speed of light,which means the radiation field will be generated at these places.The motion state of charge in lightning channel is related to the selected model.When the channel current decreases with height,part of the charge slows down to a static state along the channel.In this process,the decelerated radiation field will be generated,and the static charge in the channel will also generate electrostatic field.When calculating the electromagnetic fields of various models of lightning strikes to towers,it is found that in the close field region,the MTLE model whose current decays exponentially with height has the largest total electric field due to the relatively large electrostatic field.In the far field region,the electric field of MTLE model is the smallest because of the reduction of velocity field and the effect of channel deceleration radiation field.The calculated results of electromagnetic field of lightning strikes to towers in the paper are in agreement with those of other methods in the literature.The method can be used not only to calculate the electromagnetic field of various return shocks,but also to simulate the electromagnetic field produced by the avalanche process.Compared with other conventional methods,the method used in this paper can first judge the components of electromagnetic field by the relationship between the velocity of charge motion and the velocity of light.Then,according to the change of the motion state of charges in the channel,the position of each electromagnetic field component can be determined,and the cause of the change of the total electromagnetic field can be determined.Although the electromagnetic field of lightning return stroke can be accurately described by using the field components(electrostatic field,induction field and radiation field)associated with the short dipoles in the conventional method.However,the one-to-one correspondence between the electromagnetic field components and the physical processes that gives rise to them is lost.In this paper,based on the field equation of a moving charge,the electromagnetic field expression of the current pulse is obtained,which is divided into electrostatic field,velocity field and radiation field.From the point of view of charge motion,the physical process of the channel corresponding to the generation of the field component and the reason of the fields varying as 1/r~n can be explained.