Analysis Of Propagation Characteristics Of Electromagnetic Fields For The Lightning Striking To The Flat Ground And Tall Tower Based On Electromagnetic Field Equations Of Moving Charges

Studying the propagation characteristics of the lightning electromagnetic fields is of great significance for the error analysis of the lightning location and the correction of lightning parameter inversion.In this paper,the equivalent current pulse equation of the moving charge radiational equation and the Wait formula are used to obtain the electromagnetic fields’ propagation characteristics of the lightning striking to the flat ground and tall tower.First,the equivalent current pulse equation of the moving charge radiational equation is used to analyze the effects of horizontal distance,return-stroke speed and vertical height on the electromagnetic fields of the lightning striking to the ideal ground;then,in combination with the Wait formula,we analyze the effects of horizontal distance,return-stroke speed,vertical height,soil conductivity,and soil horizontal stratification on the electromagnetic fields of the lightning striking to the smooth and lossy ground;finally,consider the effects of different parameters on the electromagnetic fields of the lightning striking to the tall tower above the ground.The results of the method in this paper are in good agreement with FDTD and the method solves faster.The obtained propagation characteristics of the lightning electromagnetic pulse are as follows:When the lightning strikes the flat ground:(1)In the case of ideal ground,the electromagnetic fields decrease with the increasing of distance.As the return-stroke speed increases,the electric fields decrease,but the magnetic fields increase.As the height increases,the vertical electric fields decrease and the value of the surface is the largest,the horizontal electric fields increase and the value of the surface is 0,and the azimuth magnetic fields are basically unchanged.Under the same conditions,the horizontal electric fields are much smaller than the vertical electric fields,indicating that the energy of the electric fields are mainly concentrated in the vertical electric fields.(2)In the case of smooth and lossy ground,the vertical electric fields and azimuth magnetic fields can be directly replaced by the waveforms of the ideal ground,but the horizontal electric fields are different.The horizontal electric fields change from unipolar to bipolar as the distance increases.The horizontal electric fields decrease as the return-stroke speed increases.As the height and conductivity increase,the positive values of the horizontal electric fields become larger,and the negative offset become smaller,and the waveforms change from bipolar to unipolar.When the conductivity of the upper layer is greater than that of the lower layer,we can use non-layered soil with large conductivity instead.When the conductivity of the upper layer is less than that of the lower layer,we must consider the effect of the soil horizontal layering on the horizontal electric fields.When the lightning strikes a tall tower above the ground:(1)Under the ideal ground,as the distance increases,the vertical electric fields increase first and then decrease.The return-stroke speed increases and the electric fields decrease.The peak values of the vertical electric fields do not change significantly with the increase of the height.Due to the tall tower,the sensitivity of the vertical electric fields of a tall tower struck by the lightning to the height becomes smaller.The waveforms of the horizontal electric fields are bipolar and the absolute values of the negative peak decrease more with distance than the positive.As the height increases,the absolute values of the negative peak of the horizontal electric fields first increase and then decrease,and the positive peak values always increase.As distance increases,the azimuth magnetic fields decrease.The impact of the return-stroke speed on the azimuth magnetic fields is negligible.The change of the azimuth magnetic fields with the height is consistent with the vertical electric fields.(2)In the case of smooth and lossy ground,the vertical electric fields and azimuth magnetic fields of the uniform ground can be replaced by the uniform ideal ground,and the layered ground cannot be replaced.Its relationship with the horizontally layered soil is consistent with the horizontal electric fields of the smooth and lossy ground.The relationship between horizontal electric fields and distance,return-stroke speed and vertical height is consistent with the ideal ground.As the soil conductivity increases,the horizontal electric fields increase.The relationship between the horizontal electric fields and the horizontal layering of the soil is consistent with the vertical electric fields of the smooth and lossy ground.In fact,the lightning striking to the flat ground can be seen as a special form of the lightning striking to a tall tower(the height of a tall tower is 0).In the tall tower,due to the multiple reflections and transmissions of the current,the electromagnetic fields generated by the lightning striking to the tall tower appear multiple oscillations.At a short distance,the vertical electric fields of the lightning striking to the flat ground are larger than the lightning striking to a tall tower,the distance is slightly larger,and the vertical electric fields of the lightning striking to the flat ground are smaller than the lightning striking to a tall tower.The waveforms of the horizontal electric fields of the lightning striking to the flat ground and the tall tower are very different,not only the difference in peak value,but also the polarity.At the same observation point,the azimuth magnetic fields of the lightning striking to a tall tower above the ground are larger than the azimuth magnetic fields of the lightning striking to the flat ground.