Analysis of Lightning Surge on Transmission Line by New Numerical Electromagnetic Field Computation Method

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Although only the linear phenomenon had been treated in the numerical electromagnetic field calculation method, we studied how to treat an electric discharge phenomenon and added the function to simulate nonlinear phenomenon to the simulator in this research. Since the impedance changes every moment by the nonlinear phenomenon, a system equation will need be changed for every simulation time step and there is a problem which the computation time increases greatly. We noted that electric discharge and lightning arrestor are limited to be a part of transmission line, and used the algorithm which sets the number of current variables in order automatically so that it becomes the minimum change at the time of creation of a system equation. Even when the nonlinear element existed in the transmission line, it held down to the increase in about 10% of calculation time by this algorithm, and it becomes possible to simulate lightning surge within allowable calculation time.Lightning which compri … More ses electric discharge phenomena complicated from streamers to leaders and the return stroke is also a nonlinear phenomenon. It is important how a model is created in lightning surge analysis. We examined two kinds of models, the first is made by the inductive element and the second is a plasma core surrounded by space *rges. The later model could be easily programmed in the electromagnetic field analysis method, and also clarified that tne surge impedance of lightning channel becomes about five hundreds ohm and a little higher than the conventional lightning channel impedance used in circuit simulator.We have studied two methods to compute parameters for the impulse voltage expressed by the double exponential functions under given front time and tail time. The first method is based on the Newton method and shows good convergence in several iterations over wide ratio of front time and tail time. The second method uses an acceleration factor to decrease the differences of time parameters which are given by the iteration process. We can determine a double exponential function under a millisecond by both methods. However, a short tail impulse needs more number of iterations than standard lightning impulse Less