Analysis And Application Of Lightning Overvoltage On Transmission Line

Most of power transmission lines are naked, therefore they are apt to be damaged by lightning, and it may cause power interruption and damage to electrical equipment and other accidents. So study on present situation of overhead transmission line has very important significance for lightning protection. The study can also provide a reference basis for operation work and design of lightning protection.This paper has analyzed the method of the calculation of overvoltage on transmission lines by direct and nearby lightning strokes. The main contributions of the analysis are:1) The analysis of lightning induced voltage: The lightning channel is treated as a vertical monopole antenna on the ground, and starting from the Maxwell equations, the electromagnetic field around lightning return stroke channel has been calculated; the Agrawal coupling model and time-domain finite difference method are combined to derive the FDTD iteration formula of voltage and current of each node on transmission line, and the soil resistance derived using similar methods has deal with the frequency-dependent parameters that exist in coupled model; using the above theory, it has calculated the lightning induced voltage on two kinds of line structure of 10kV class separately, which are triangular wiring and aligned wiring, and various factors affecting the voltage distribution have been analyzed.2) The study on direct lighting overvoltage: The study on direct lighting overvoltage trip rate includes straight lightning stroke on tower top (backstroke) and round stroke to conductor (shielding failure).Using the electrical geometry model and exposure distance to calculate the trip rate caused by shielding failure; based on the principles of IEEE flash program, using probability statistics method to calculate the trip rate caused by backstroke; applying this method, the lightning trip rates of Baoding 220kV double circuit transmission lines have been calculated, and according to the results it has proposed the measures which should be taken to improve the line insulation level.