Calculation of Transient Electromagnetic Field around a Transmission Line Subjected to Lightning Strokes zyx Babak Porkar zyxwvuts , Siyamak Porkar and Ali Naderian Jalzromi Abstract: In this paper, a new method for the calculation of electromagnetic fields around a trans- mission line subjected to a lightning strike is described and discussed. The electric fields and magnetic fields are presented graphically as a function of spatial coordinate, as a function of time and zyxwvut as a function of both. It is believed that this exact solution have not been published before. First, a double exponential lightning surge current is injected into a transmission line. Once The temporal variations of current is known, then electric and magnetic fields can be calculated by using the field expressions for electric dipoles over infinitely conducting ground. As the calculation was done for each frequency, temporal and spatial distributions of the electromagnetic fields are obtained by an inverse Fourier transformation of all these responses. I. INTRODUCTION In recent years, study of interference effects from AC power lines in pipelines, railways, communication lines and other such structures has resulted in numerous research reports and papers. Not only the steady-state interference but also a transient interference become significant due to increasing usage of IC and digital circuits in these days. But the propagation effects on the transients zyxwvutsr as they propagate along the power line are caused that calculation electro-magnetic fields due to such as waveforms is complex [ 1-61. The calculation transient electromagnetic fields around transmission line are similar to lightning channel. In the calculation of the electric fields, a lightning channel is decomposed into numerous dipoles, and the complex amplitude of a dipole is calculated in the frequency domain postulating a return-stroke model. After calculating the electric fields produced by all the dipoles, they are synthesized to yield the solution in the time domain. The electric field produced by a dipole having any inclination can be calculated through those produced by vertical and horizontal dipoles. Numerical calculation of the complete solution of the electric fields over lousy ground was produced of the complete solution of time consuming due to the existence of the Sommerfeld integrals zyxwvuts [7]. In this Babak Porkar is a Ph.D. student at the Electrical Engineering Department, Sharif University of Technology, Tehran, Iran (email: babak_porkar@meht..sharif.edu) Ali Naderian Jahromi is a Ph.D. student at the Electrical and Computer Engineering Department, University of Tehran, Tehran, Iran (e-mail: a.naderian@ece.ut.ac.ir ) Siyamak Porkar is a MS student at the Electrical Engineering Department, Amirkabir University of Technology, Tehran, Iran power line, with mentioned method in lightning channel has been used. The propagation effects on the transient as they propagate along the line are considered zyxwv by dividing power lines into short distance lines and modeling those by J.Marti model in EMTP. Also in this step and in this paper: 1) It is assumed that power line conductors that are straight horizontal wires carry the lightning current. For considering conductor sag, the current element can be divided in to a vertical dipole and a horizontal dipole, and the fields from both may be superimposed to provide the fields produced by the arbitrarily oriented source [7-81. 2)It is assumed that ground is perfectly conducting . Sommerfeld first evaluated the electric field due to a dipole over finitely conducting ground and the results were given in terms of integrals. Many researchers have considered different approximations for these integrals. Recently, Zeddom and Degauque [9] evaluated these Sommerfeld integrals and comp-ared the results with these well known approximations. Their results show that the fields over finitely conducting ground can be well represented by the results of Norton [ 101 among others. 11. METHOD OF ANALYSIS A. Electric Dipoles Over a Prefect Ground The simplest case of a source located near a conducting object is that of an arbitrarily orientated current element located over an infinite, prefectly conducting ground plane, as illustrated in Fig. 1. In this figure, the ground plane lies in the x-y plane at z=O. Ima*CkucFIP Fig.1. Geometry for a vertical or x-directed horizontal current element over a prefect ground plane. For analysis purpose, the current element can be divided into a vertical dipole and a horizontal dipole, and the fields from both may be superimposed to provide the fields produced by the arbitrarily oriented source. Generally, the vertical current element will radiate more efficiently than the horizontal element in 0-7803-7989-6/03/$17.00 02003 IEEE 258