Analysis And Calculation Of Lightning Induced Voltages On Overhead Lines Due To Nearby Lightning

Most overhead distribution lines are exposed in the air, so they are apt to be damaged by lightning caused overvoltage, which will interrupt power supply. Since the damage of direct lightning is worse than induced lightning, so the research has mainly focused on direct lightning long before, while the investigation of induced lightning is rather less. But recent researches indicate that, instead direct lightning, the induced one produces exceeding 90% flashover of 10kV overhead distribution lines. Therefore, it's significant to study the analysis and calculation of lightning induced overvoltage on overhead distribution lines.First, the mechanism and characteristic of nature lightning are described at first, six engineering models about return-stroke current are compared and discussed. MTLL model is regarded as the most promising one, and then its base current waveform and expression are presented in this paper.Secondly, to predict lightning electromagnetic fields, Quasi-Images method and dipole method are used to combine Maxwell's equations for the formulation of vertical discharge channel. By assumption of a dipole model, the horizontal and vertical components of electric field, Er and E,, as well as magnetic field BΦare respectively derived. For field points on ground, analytical solution can be achieved, while the lightning electromagnetic field in arbitrary space position, numerical method is employed.Then, we analyze transmission lines transient process. Begin with transmission line circuit model -- telegraph equations (a hyperbolic partial differential equations), a simple and quick and effective numerical solution in time domain has been deduced in the aid of circuit theory and computational mathematics. In this thesis, the partial differential equations has been discretized by FDTD formulae, which results in a brand-new computational algorithm. Furthermore, boundary conditions have been impressed on the basis of lumped equivalent circuit model.Finally, Voltage and current waveforms has been simulated in terms of different simple boundary conditions and initial conditions, which compared with EMTP-ATP, achieving satisfactory results. The detailed analysis of a illustrated example has provide useful conclusions on return stroke velocity and amplitude, different height of overhead line.