Electromagnetic Fields Calculation Of Lighting Return-Stroke Based On FDTD Method

In this paper, a physical model for nature lightning is built, analytical and numerical methods for calculating lightning electromagnetic plus (LEMP) are studied, computer program about numerical calculation and simulation is developed and implemented in Grid computing environment. The main contents include the following aspects.About current models of lightning, the mechanism and characters of nature lightning are described at first, six engineering models about return-stroke current are calculated and discussed, and features of every model are compared. Especially, MTLL model is studied and discussed, its base current waveform and expression are presented in this paper.About theoretic calculation for lightning electromagnetic field, Quasi-Images method and dipole method are used. By using these two methods, Maxell's equations for vertical channel are solved. By building a dipole model for lightning, differential equations regarding horizontal electric field Er , vertical electric field E zand tangential magnetic field Bφof any field point in lightning space are derived. For E zand Bφof field points on ground, analytical formulations are derived directly.About numerical calculation for lightning electromagnetic field, two numerical methods based on analytical formulas are studied. The numerical method from FDTD formula is obtained by scattering lightning current at time and space, and the numerical method from time-varying field formula is obtained by scattering lightning current at time. With finite difference time domain (FDTD) method, lightning space is dispersed and electromagnetic fields for whole free space are solved. Errors between two methods are analyzed and compared, the results indicate values of electric field and magnetic field from two numerical methods are consistent with classical analytical methods. With the proposed FDTD method, the effect of channel height, return-stroke speed and ground permittivity on electromagnetic field is analyzed, and some significant conclusions are obtained.Finally, the work in this paper is summarized and main contents about the study are indicated, which is method for calculating oblique channel, one numerical method, finite difference time domain (FDTD) method, for calculating electromagnetic field of any point in lightning space is presented. Errors between two methods are analyzed and compared, the results indicate FDTD method is an effect method for calculation of lightning electromagnetic field. With the proposed FDTD method, the effect of channel height, return-stroke speed and ground permittivity on electromagnetic field is analyzed. Besides, the further research problems are indicated.