| The radiated electromagnetic field generated by lightning striking towers during the return stroke is a great threat to the surrounding electrical equipment.It is of great significance to study the spatial distribution,propagation characteristics and various factors affecting the radiated electromagnetic field of lightning striking towers.Under the action of great lightning current,the corona effect on the surface of high tower may cause the change of lightning current propagation characteristics along the high tower,and then affect the radiation electromagnetic field,which is often ignored in previous analysis.The finite difference time domain(FDTD)method has certain advantages in the calculation of lightning electromagnetic field and the simulation of corona on conductor surface.In this paper,the electromagnetic model of lightning tower considering side corona effect is established by FDTD method in two-dimensional cylindrical coordinate system,and the possible influence of corona effect is simulated and analyzed efficiently by Huygens subgrid technology.In the simulation,the high tower is simplified as an ideal cylindrical conductor with a certain radius,and the corona effect is represented by the high conductivity area developing radially around the high tower.Firstly,the electromagnetic model of lightning tower is established based on FDTD method,and the influence of different excitation sources on the current distribution of lightning tower is simulated and compared.The results show that the ideal voltage source can better simulate the refraction process of waves at the top of the tower than the ideal current source,and is more suitable for simulating lightning strikes on the tower for a long time.At the same time,the reflection and refraction coefficients at the top of the tower can be further adjusted by adding lumped resistors with certain resistance values at the top of the voltage source and the bottom of the lightning channel.After that,Huygens subgridding technology is introduced into the FDTD analysis of lightning-struck towers,which realizes that a small space step is adopted in a small area including lightning channels and towers,and a large space step is still adopted in other areas,thus greatly improving the calculation efficiency.On this basis,this paper deeply tests the possible errors of sub-grid calculation model in lightning electromagnetic field calculation.The results show that when the inner boundary on the right side of the sub-grid area is close to the axis,and the space ratio between the main grid and the sub-grid is large,there may be some errors in the calculation results of the improved sub-grid calculation model,which can be reduced by slightly expanding the distance from the inner boundary to the axis.Finally,in the subgridding FDTD calculation model,the influence of corona effect of lightning striking tower is simulated and analyzed efficiently.The results show that the corona on the side of the tower will cause additional attenuation when the current wave propagates along the tower under the extremely high lightning current,and then the waveforms of vertical electric field and horizontal electric field radiated by lightning striking the tower will change,and the influence degree will decrease with the increase of observation distance.Among them,the vertical electric field is greatly affected,the overall trend of its waveform remains unchanged,and the peak value and subsequent electric field values are reduced;The influence of horizontal electric field is relatively small,and its peak value also decreases,but the degree of decrease is weakened.At the same time,the subsequent falling waveform after the peak value becomes gentle and the attenuation of electric field value slows down.The above effects are significantly reduced with the decrease of peak input current and the increase of tower radius.In addition,due to the different polarity of corona,the influence of corona is greater in positive lightning than in negative lightning. |
PDF Full Text Request