Time-domain Numerical Analysis Of Lemp Coupling Of Overhead Lines

As an indispensable infrastructure for the country,the power system plays a decisive role in the development of modern industry and the convenience of daily life.As an important part of the power system,overhead lines are widely used in many areas such as power grid systems and railway systems.Most of the power overhead lines are exposed to the outside environment and are highly susceptible to electromagnetic pulse interference in the environment.Lightning as a high-intensity discharge phenomenon occurs frequently in the natural world,and the strong electromagnetic pulse generated by it causes a great threat to the surrounding transmission lines.With the rapid development of microelectronics technology,the operating frequency of electronic components and circuits is greatly increased while the operating voltage is continuously decreasing.Therefore,the current generated by the electromagnetic pulse in the space to the cable in the shield body is increasingly destructive to the electronic circuit components.Furthermore,the analysis,prediction and protection of the strong electromagnetic pulse on the power system transmission line interference has important research significance and engineering application value for improving the stability and reliability of the power system.Since overhead line cables usually need to span over hundreds meters and the excitation signal band is very wide,general simulation software and numerical calculation methods are less computationally efficient.In view of this situation,lightning retrun-stroke model was established to analyze the interference on overhead line excited by LEMP,the excitation electric field distribution was calculated by the finite difference time domain method(FDTD).In order to get the induced voltage on overhead lines,transmission-line equation was discretized by FDTD.The reliability of the method was proved by comparing the obtained results with those of classical literatures.Compared with the traditional FDTD method,there is a great advantage in terms of calculation speed and memory usage.Then,three observation points at different positions on the overhead line are selected to calculate the induced voltage,and the effect of the overhead line coupling effect with distance changes is obtained.After that,the current speed and induced voltage strength are obtained by using different speeds of the channel current.The paper also explored the relationship between the height and number of overhead lines and the induced voltage.Finally,the reasons behind some of the phenomena are analyzed and the rules and methods of lightning protection for overhead lines are summarized.Finally,the paper introduces the characteristics of HEMP and compares the nuclear electromagnetic waveform parameters under different standards.After that,a variety of intensive electromagnetic pulse environment and shielding cavity model are established to solve the coupling problem of the transmission line in the non complete shielding cavity of the power system equipment.The coupling response law of the shielding cavity by the nuclear electromagnetic pulse is found through simulation and Simulation of the rectangular,circular,porous and other apertures.In order to explore the effect of different excitation wave types on coupling effect,the simulation of different polarization modes and incidence angles was carried out.The coupling law between polarization mode and incident angle is obtained by analyzing the results.Different shielded cables were selected for comparison and simulation.It was found that multi-conductor cables have better shielding effects than single-conductor cables.