Numerical electromagnetic analysis of lightning-induced voltage over ground of finite conductivity (original) (raw)
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Journal of Electrostatics, 2004
In the present paper, transient-induced voltages on a distribution line over finitely conducting ground, which are associated with lightning to a 200-m high stack, have been analyzed by Numerical Electromagnetics Code (NEC-2). An electromagnetic model (EM) of a lightning channel, which contains additional distributed inductance to simulate the reduced propagation velocity of lightning current, has been employed. Validity of the employed model which incorporates a tall structure and a lightning channel has been discussed by comparing calculation with measurements. r
IEEE Transactions on Electromagnetic Compatibility, 2021
The paper provides the implementation procedure, the validation and some considerations on the computational efforts of the developed analytical expressions for the lightning electromagnetic fields presented in the companion paper. The validation is presented with different configurations in terms of channel-base current, ground conductivity and distance to the lightning channel, comparing the obtained results with the numerical integration of the classical formulas. The comparative analysis shows a perfect agreement between the proposed analytical approach and reference numerical simulations. Moreover, the computational effort of the proposed method is discussed, focusing the attention on the choice of the points in which the channel has to be divided in order to maximize the CPU time savings without losing accuracy. Index Terms-Lightning electromagnetic fields, Channel base current, Engineering models I. INTRODUCTION ne of the most important causes of damages in distribution systems are lightning-induced voltages. As pointed out in Part I, their evaluation has been addressed by many researchers in the last years. It is important to note that all the proposed models for the computation of induced voltages rely on the knowledge of the electromagnetic fields. In the literature, their evaluation is usually achieved in two steps: 1) the electromagnetic fields in the presence of a perfectly conducting ground are computed assuming a vertical lightning channel [1-3], and 2) the effect of the ground conductivity is taken into account with the Cooray-Rubinstein formula [4, 5].
Journal of Geophysical Research: Atmospheres, 2008
1] In this paper, the developed formulation, which we shall call the ''reference'' one, is used to assess the validity of the most popular simplified approach for the calculation of the lightning electromagnetic field over a conducting earth, namely, the Cooray-Rubinstein (CR) approximation. This formula provides a simple method to evaluate the radial component of the electric field which is the component most affected by the finite ground conductivity and which plays an important role within the Agrawal et al. (1980) field-to-transmission line-coupling model. Several configurations are examined, with different values for the ground conductivity and different field observation points. A thorough analysis of all the simulated field components is carried out and comparisons are also made with the ''ideal'' field, namely, the field that would be present under the assumption of perfectly conducting ground. It is shown that for channel base current typical of subsequent strokes and for very low conductivities, the CR formula exhibits some deviations from the reference one but it still represents a conservative estimation of the radial field component, since it behaves as un upper bound for the exact curve. The developed algorithm is characterized by fast performances in terms of CPU time, lending itself to be used for several applications, including a coupling code for lightning induced overvoltages calculations.
Lightning Electromagnetic Fields Computation: A Review of the Available Approaches
Energies
Lightning represents one of the most critical issues for electrical infrastructure. In dealing with overhead distribution line systems, indirect lightning strikes can lead to induced voltages overcoming the critical flashover value of the line, thus damaging the insulators. The computation of lightning-induced voltages requires the modeling of the lightning current, the evaluation of the lightning electromagnetic fields and the solution of the field-to-line coupling equations. The numerical calculation of the lightning electromagnetic fields is time-consuming and is strongly dependent on the lightning channel modeling and soil properties. This article presents a review of the most widely adopted methods to calculate the lightning electromagnetic fields, starting from the classical formulation, which requires numerical integration, and highlighting the most effective approaches that have been developed to reduce computational effort. This is done first for the case of a perfectly con...
Evaluation of Lightning-Induced Voltages Over a Lossy Ground by the Hybrid Electromagnetic Model
IEEE Transactions on Electromagnetic Compatibility, 2009
In this paper, the hybrid electromagnetic model is applied to calculate lightning-induced voltages over a lossy ground. Results provided by this model are compared with experimental data obtained from a reduced-scale model and with results simulated by the numerical electromagnetics code. Good agreement is achieved in all cases.
Numerical Electromagnetic Analysis of Lightning Current in Elevated Strike Objects
2006
In this paper, an analysis of electric and magnetic fields radiated by lightning first and subsequent return strokes to tall towers using Numerical Electromagnetic Code (NEC-2) is presented. The advantage of the analysis using NEC-2 is that it can accurately compute the current distribution along a conductor system by the method of moments. It is shown that the presence of a tower tends, in general, to increase substantially the electric and magnetic field peaks. The presented results are shown to be consistent with the measured current in lightning strokes to the CN Tower and of the associated electromagnetic fields measured 2 km away.
A Mathematical Model for the Transient Lightning Response from Grounding Systems
Progress In Electromagnetics Research B, 2014
With the Fast Fourier Transform (FFT), a mathematical model for accurately computing distribution of a lightning currents flowing along a high voltage a.c. substation's grounding system buried in half infinite homogenous earth has been developed in this paper. It is a hybrid of Galerkin's method of moment (MoM) and a conventional nodal analysis method. The model can directly calculate the distribution of both branch and leakage currents along the grounding system. A dynamic state complex image method and a closed form of Green's function of a dipole or monopole in the half infinite homogenous earth model are introduced into this model to accelerate calculations of mutual impedance and induction coefficients. Analytical formulae for the mutual induction and impedance coefficients have been developed to accelerate the calculation for near field case by using Maclaurin expansion. With the inverse FFT, the model can be used to study the transient lightning response of a grounding system.
Evaluation of Lightning Horizontal Electric Fields Over a Finitely Conducting Ground
Lightning electromagnetic fields radiated during the return stroke phase may induce overvoltages on overhead conductors. These transients can damage sensitive electronic equipment and provoke line flashovers, thus degrading the performance of distribution and telecommunication networks. This paper presents and discusses the characteristics of the horizontal component of the electric field produced by negative cloud-to-ground flashes during the return stroke phase. The analysis considers the influences of the distance between the return stroke location and the observation point, the soil type and the stroke current propagation velocity. The TL model is adopted for the determination of the current distribution along the return stroke channel, whereas the effect of the finite ground conductivity is taken into account by using the Cooray-Rubinstein approximation. The results show that, regardless of the ground conductivity, the distance from the lightning strike point has a great influe...
2014 International Conference on Lightning Protection (ICLP), 2014
We use a full-wave finite-element-based solution of Maxwell's equations for the evaluation of lightning electromagnetic fields inside a vertically stratified, two-layer ground (oceanland mixed propagation path) and their induced currents on the shield of buried cables. For "normal" incidence (with respect to the ocean-land interface), it is shown that the vertical electric field is the component most affected by the ocean-land mixed path when the observation point is close to the ocean-land interface (i.e., 5 m or so). For "oblique" incidence, however, depending on the angle of incidence and the distance between the observation point and the ocean, all the field components are reduced by the ocean-land interface. For the calculation of induced currents, and for the case of a parallel layout (cable laying in parallel to the ocean-land interface); 1) for a strike to the land, when the cable is buried in the soil and the distance to the ocean is greater than about 100 m, the effect of the ocean is negligible. 2) For a strike to the ocean, the induced current magnitudes are appreciable only when the cable is entirely within the land. For the case of a perpendicular layout (cable perpendicular to the ocean-land interface); 1) for a strike to the ocean, when the cable is totally buried in the ocean, the effect of ocean-land mixed propagation is negligible. However, when the cable extends into the land through one end, the induced currents increase at both ends with increasing length of underland portion. 2) For a strike to the land, when the cable is located entirely inside the land, the effect of ocean-land mixed path on the induced currents at both ends is negligible. However, as the cable extends into the ocean, a remarkable enhancement in the induced currents is observed for the termination located inside the land. This enhancement can be as high as a factor of 2 with respect to the case of a cable in homogeneous soil characterized by the properties of the land.