Research On The Response Of Overhead Transmission Lines And Cables Excited By High-altitude Electromagnetic Pulse

High-altitude electromagnetic pulse(HEMP)is a kind of pulse with high intensity,wide frequency band and wide action range.Its influence on power system has been paid much attention.In this thesis,the response of overhead transmission lines and cables excited by high-altitude electromagnetic pulse on the lossy earth is studied.The main research results are presented as follows:1.Based on iterative and adaptive perturbation technique and a single variable finite-element time-domain(FETD)method,this thesis propose a method for solving the response of overhead transmission lines and cables excited by high-altitude electromagnetic pulse on the lossy earth.The HEMP coupling effect of the nonuniform transmission lines can be obtained by the iterative solution of the uniform transmission line model,which is equivalent to the uniform transmission lines with additional distributed sources.The accuracy of the method is verified by comparing it with the calculations results of the bivariate FETD method.Based on this method,the influence of sag on the induced voltage of overhead transmission lines is analyzed.The results show that the horizontal electric field and the vertical electric field change along the line after considering the sag,which leads to the decrease of the peak value of induced voltage at the line end and the increase of the peak value of voltage at the line midpoint.Therefore,it is necessary to consider the influence of sag when calculating the HEMP coupling effect of transmission lines.2.Based on Sunde’s formula,Timotin’s formula and Orzan’s formula,a simple method to describe the ground resistance is derived.In view of the early and late time responses of the ground resistance,the characteristics of the poles and residues are discussed respectively,and the time domain general expressions of the transient ground resistance under different soil electromagnetic parameters are obtained.Since the expression has the form of exponential function,the ground resistance can be evaluated by a recursive convolution,which can effectively improve the computational efficiency.3.The effects of maximum sag,earth conductivity,incident pitch Angle,incident polarization Angle and incident azimuth on the responds of overhead transmission lines are quantitatively calculated and analyzed by using the method presented in t his thesis.The simulation results can provide a reference for the circuit design of power system and the protection of strong electromagnetic pulse.