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The evaluation of the lightning performance of overhead lines requires, mainly for distribution lines, the calculation of the voltages induced by nearby lightning strokes hitting the ground. Generally, when calculating lightning-induced voltages using the time-domain approach and the TEM assumption, the most time-consuming stage is the calculation of the source terms of the coupling equations, which means, in turn, the electromagnetic field radiated by the lightning channel. Hence, simplified approaches are still desirable in order to save computational time. Analytical solution of the lighting-originated electric- and magnetic field is available in literature for the case of an ideal transmission-line (TL) return-stroke model with channel-base current having a stepwise waveshape. This paper describes an analytical approach that applies to the case of a general waveshape of the channel-base current, based on the piecewise straight-line approximation, in cylindrical coordinates, which is functional when using the TL return-stroke current model and the Agrawal et al. coupling model. This paper reports the exact solution for the case of trapezoidal waveshape of the current at the base of the channel and the analytical solution for the case of piecewise linear waveform. [ABSTRACT FROM AUTHOR]

This paper presents a new physical model for shielded slow-wave coplanar waveguide structures. This lossy electrical model is based on physical behavior of the transmission lines. It allows a better understanding of the losses distribution along the structure. The ohmic losses in the coplanar strips, as well as the ohmic losses and the eddy current losses in the floating shield strips are studied for transmission lines having different geometrical dimensions and hence electrical characteristics. The model is then validated on different CMOS technologies and leads to the efficient optimization of the slow-wave transmission lines, especially concerning the floating shield dimensions. [ABSTRACT FROM AUTHOR]

In this paper, a time-domain variant of the generalized telegrapher's equations for transient electromagnetic field coupling to a finite-length wire above a lossy half-space is derived. The approach is fully based on the thin-wire antenna theory. The lossy ground effects are taken into account by means of the reflection coefficient approximation. The obtained equations are handled numerically via the Galerkin–Bubnov indirect boundary element method. Computational examples are presented for the case of a single-wire line excited by an electromagnetic pulse excitation source. The obtained results for the induced current along the line are compared with those obtained using 1) the method of moments solution of the electric field integral equation implemented in the numerical electromagnetics code (NEC-4), and 2) the transmission line (TL) theory. It is shown that the results obtained by the proposed method are in excellent agreement with those of NEC-4. It is also shown that the TL approximation yields in general results which are in reasonably good agreement with the full-wave results, especially for the early time response and even beyond the limits of the accuracy of the TL theory. The TL theory can, however, give accurate results only for times before the arrival of the first reflection from the TL terminations and it fails to reproduce accurately the dispersion effects occurring after the first reflection. [ABSTRACT FROM AUTHOR]

A new method for the numerical simulation of the stochastic electromagnetic environment of a mode-stirred chamber is presented in this paper. This method is based on the plane-wave integral representation for the fields and uses a Monte Carlo simulation to replace the analytical integration by numerical summation. Therefore, a field generator is implemented as a program. The numerically generated field distributions and spatial correlation functions are compared to the analytical solutions for the validation of the field generator. With this generator, the field coupling to a simple transmission-line structure can be numerically simulated. The coupled current or voltage has to be regarded as a stochastic value as well, and therefore, parameters like the mean value and the standard deviation along the line are calculated. For the special case of a matched line, an analytic solution is introduced in order to validate the numerical results. The simulation also allows for investigating the statistical distribution and correlation of the coupled current along the transmission line. Numerous simulated results are compared with measurements. [ABSTRACT FROM PUBLISHER]

The calculation of voltages induced by external electromagnetic fields on multiconductor transmission lines (MTLs) has been the subject of several studies. In this paper, discrete equations for MTLs exposed to incident fields are derived based on the time-domain finite-element method and the backward differentiation formula. Based on these equations, a value-delivery table characterizing the MTLs is presented. Combining this table with modified node analysis formulation, it is convenient for analyzing the responses of transmission lines composed of complex termination networks or complex transmission-lines networks. The validity and efficiency of the proposed algorithm is demonstrated using several examples. Finally, a 1-km 35 kV overhead line above an imperfectly conducting ground is studied, and the influences of ground wire and a metal-oxide arrester to the lightning-induced voltage are both discussed. [ABSTRACT FROM PUBLISHER]

A novel high-efficient two-step finite-difference time-domain (FDTD) method is proposed to analyze the lightning-induced voltages on transmission lines (TLs) in this paper. The proposed method includes two steps. The first step is to calculate, using the 2-D FDTD method, electromagnetic fields that are radiated from a vertical lightning channel and illuminate the nearby TLs. The second step is to calculate, using the 3-D FDTD method, the electromagnetic response of the TL that is illuminated by the incident electromagnetic fields added at the total field–scattered field connecting the boundary of the 3-D space. To validate the proposed two-step FDTD method, the results calculated using the two-step FDTD method are compared with those calculated with Agrawal coupling model, and with those calculated using the 3-D FDTD method. The two-step FDTD method shows high computational efficiency in analyzing lightning-induced voltages on TLs. [ABSTRACT FROM AUTHOR]

Four model types that could be used to theoretically approximate lightning events currently exist. These are namely gas dynamic (physical) models, electromagnetic models, distributed-circuit models, and “engineering” models. In this paper, a modified transmission line (TL) “engineering” modeling approach, which incorporates the presence of a tall object in the lightning path is adopted. The associated discontinuity at the lightning channel front is treated by introducing reflected and transmitted components, with constituents that are less influential omitted. All computations are performed in the time domain. The considered tall structure is the CN Tower and it is represented by either one, three, or five transmission line sections connected in series. The lightning channel is represented by two more transmission line sections of variable length. The models allow for calculation of current at any height of the CN Tower or the lightning channel and at any time, as needed for determination of the electric and magnetic fields at a distance. The approach is applicable to any other tall structure. [ABSTRACT FROM AUTHOR]

This paper discusses the issue of skin-effect impact on a current's distribution. It presents an analytical approach for determining temperature distribution by using the Electromagnetic Field Analysis Tool's two-dimensional (2-D) program (ELEFANT 2D) over the cross sections of tube-type conductors. Using this implemented model, the authors determine the conductor's current density by taking into account the skin-effect impact on a multi-layered bare conductor by the overhead power transmission lines of the ACSR 490/65 mm² type, and the optical cable of the optical ground wire (OPGW) type. An ELEFANT 2D is given an enabling determination of temperature distribution over the tube-type conductor cross section. The authors have developed, using this program, a computerized mathematical model for temperature determination by considering the skin effect in a multilayer ACSR 490/65 mm² conductor, and the optical cable of the OPGW type. The results show temperature distribution in individual layers of the ACSR 490/65 mm² conductor and the OPGW cable by adiabatic heating at different short-circuit currents. [ABSTRACT FROM AUTHOR]