Frequency domain modeling of nonuniform multiconductor lines excited by indirect lightning

Abstract

This paper describes a methodology in the frequency domain for the modeling of a multiconductor transmission line excited by a lightning stroke hitting the nearby ground, considering also variations of the line parameters along its length (nonuniform line). Modeling of the line excited by an external field (also known as illuminated line) is based on Taylor’s formulation, while the incident electromagnetic field representing the nearby lightning stroke is computed following the expressions defined by Master and Uman. This formulation computes a nonuniform electromagnetic field dependent of the lightning’s point of impact with respect to the line. A nodal form is used to completely describe the field excited line, including the effect of the incident field by means of current sources connected at the line ends. From this description, nodal voltages are computed in the frequency domain, using the inverse numerical Laplace transform algorithm to obtain the corresponding time responses. As an initial verification of the method, a comparison with an experimental result previously published is provided. As a second application example, a test case is used to analyze the effect of the point of impact on the magnitude and waveshape of the transient overvoltages obtained, as well as the effect of line’s sagging between poles. Finally, it is demonstrated that the inclusion of lightning arresters can be considered in this frequency domain model by means of a combination of a piecewise linear approximation and the superposition principle.