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Abstract-This paper presents a novel time-harmonic electromagnetic model for determining the current distribution on conductor grids in horizontally stratified multilayer medium. This model could be seen as a basis of the wider electromagnetic model for the frequency-domain transient analysis of conductor grids in multilayer medium. The total number of layers and the total number of conductors are completely arbitrary. The model is based on applying the finite element technique to an integral equation formulation. Each conductor is subdivided into segments with satisfying the thin-wire approximation. Complete electromagnetic coupling between segments is taken into account. The computation of Sommerfeld integrals is avoided through an effective approximation of the attenuation and phase shift effects. Computation procedure for the horizontally stratified multilayer medium is based on the successful application of numerical approximations of two kernel functions of the integral expression for the potential distribution within a single layer, which is caused by a point source of time-harmonic current. Extension from the point source to a segment of the earthing grid conductors is accomplished through integrating the potential contribution due to the line of time-harmonic current source along the segments axis.

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Abstract-Exact formulas for internal impedance per unit length of tubular cylindrical conductors energized by time-harmonic current involve Bessel functions. These functions are defined by infinite series, which yield unstable and often erroneous results for complex arguments of large magnitudes. Although it is well known how to evaluate Bessel functions numerically and many routines are now available to perform the actual computation, the available software routines often fail when computing equations that consist of a product and a quotient of Bessel functions under large complex or real arguments. For such cases, different approximate formulas can be used. In this paper, three types of approximate formulas for internal impedance of tubular cylindrical conductors are compared with respect to numerical stability and accuracy.

SUMMARYThe aim of the proposed paper is to present an effective numerical algorithm for the computation of Heidler function parameters. The basic six channel-base current quantities can be prescribed: current peak value, front duration, time to half value, current steepness factor, charge transfer at the striking point and specific energy. The approximation of the unknown three lightning current parameters for Heidler function is achieved using the least squares method. For the purpose of better convergence, the Marquardt least squares method has been applied. The proposed algorithm can be successfully applied for lightning current modelling in power engineering as well as in research on electromagnetic compatibility.