Study On Lightning Current Model And Its Transient Electromagnetic Effect

With the improvement of intelligence and informationization of buildings and power system equipment,the complexity of lightning protection work increases,so it is of great practical significance to conduct more in-depth research on lightning protection.The electromagnetic effect of lightning is mainly caused by lightning current.firstly,the lightning current double exponential model,Heidler model and pulse function model are established by MATLAB software.The frequency domain function and peak accumulation function of three lightning current models are derived by using Fourier fast transform(FFT),and then the frequency domain waveform diagram and normalized peak ratio spectrum diagram of the three models are obtained The energy spectrum functions of three models of lightning current are derived by frequency domain integration method,and the energy spectrum waveforms and energy ratio characteristic diagrams of the three models are further obtained.Secondly,around the problem of internal electromagnetic interference when the building is directly hit by lightning,the transmission line network model of the building lightning protection system is established,and the frequency domain distribution of lightning current in the branch conductors of the lightning protection system is calculated without considering the coupling.In this model,the conductors do not need to be segmented and the coupling is ignored,so the calculation amount is small.The temporal distribution of lightning current in building lightning protection system is obtained.In view of the same problem,on the one hand,the results calculated by this method are compared with those in the international lightning protection standard IEC62305-4,and on the other hand,the analysis results considering coupling and excluding coupling are compared,thus verifying the accuracy of this method;In order to improve the calculation accuracy of branch conductor current,the conductors in the lightning protection system of buildings are finely divided.According to the lightning current distribution of each conductor in the building lightning protection system,the transient magnetic field distribution in the building is calculated,and the electromagnetic interference of direct lightning to indoor electronic equipment can not be ignored through analysis.The transient magnetic field near the lightning point and the main lightning current discharge channel is strong,and the attenuation of the magnetic field in space is serious,which provides a basis for studying the electromagnetic interference of electronic equipment in buildings during lightning stroke.According to the accurate analysis of transient electromagnetic phenomena when wind turbine encounters direct lightning,the lightning protection system model of wind turbine is established,the network equation of wind turbine transmission line is solved in frequency domain,the current distribution of all conductors in lightning protection system is obtained,and the oscillation phenomenon of waveform in the process of solving current is further analyzed and improved.Then,according to the conductor current distribution,the transient electromagnetic field distribution in the fan is calculated.The lightning protection system and its electrical parameters during lightning stroke are analyzed.The influence of lightning current waveform parameters,different lightning rod installation points,conductor diameter,conductor conductivity and grounding resistance on the transient electromagnetic field inside the lightning protection system is quantitatively analyzed by using the method designed in this paper.The influence laws of the above factors on the transient electromagnetic effect of direct lightning are obtained by comparison.In order to reduce electromagnetic interference,this paper puts forward some reference opinions from the design and installation of lightning protection system.