1,022 research outputs found
Modeling lightning strikes to tall towers
No full textIn this chapter, we present a review of recent progress in the modeling of lightning strikes to tall structures. Since some tall structures are struck by lightning several tens of times per year, they can be used as ground-truth to measure and calibrate the location accuracy of lightning location systems. In addition, knowledge of the transient processes in tall objects when they a subjected to a lightning strike allows us to use them to calibrate the lightning return stroke currents reported by lightning detection and location systems. Tall objects constitute also a primary source of data from which channel-base lightning current statistics are obtained. These statistics are in turn used to improve the design of lightning protection devices and systems. This chapter is organized as follows: Section 5.2 presents a review of the extension of lightning return stroke models to include the presence of an elevated strike object. Section 5.3 deals with the computational methods for the evaluation of the electromagnetic fields generated by lightning strikes to tall structures. A review of available data on lightning currents from lightning to tall structures is presented in Section 5.4. Finally, a summary is given in Section 5.5.SCI-STI-F
Colophons as a Tool for Mapping the Literary History of Bali : Ida Pedanda Made Sidemen - Poet, Author and Scribe
No full textRubinstein Raechelle. Colophons as a Tool for Mapping the Literary History of Bali : Ida Pedanda Made Sidemen - Poet, Author and Scribe. In: Archipel, volume 52, 1996. pp. 173-191
Field-to-Transmission Line Coupling Models With Special Attention to the Cooray–Rubinstein Approximation
No full textThere are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal–Price–Gurbaxani model, the Taylor–Satterwhite–Harrison model, and the Rachidi model. The Cooray–Rubinstein approximation is a procedure used by scientists and engineers to estimate the horizontal electric field from the lightning that is used in the induced voltage calculations for lines located over a finitely conducting ground. The Cooray–Rubinstein approximation is usually incorporated in calculating the induced overvoltages using the Agrawal–Price–Gurbaxani model. In this article, it is shown how this approximation could be incorporated into the other two coupling models. The resulting coupling equations are compared to each other by calculating the voltages induced on two idealized overhead transmission lines.SCI-STI-F
Interaction of lightning-generated electromagnetic fields with overhead and underground cables
No full textIn this chapter, we discussed the TL theory and its application to the problem of lightning electromagnetic field coupling to transmission lines. After a short discussion on the underlying assumptions of the TL theory, we described seemingly different but completely equivalent approaches that have been proposed to describe the coupling of electromagnetic fields to transmission lines. The field-to-transmission line coupling equations were then extended to deal with the presence of losses and multiple conductors and expressions for the line parameters, including the ground impedance and admittance were presented. The time-domain representation of the field-to-transmission line coupling equations, which allows for a straightforward treatment of nonlinear phenomena as well as the variation in the line topology, was also described. Solution methods in the frequency domain and in the time domain were given and application examples with reference to lightning-induced voltages were presented and discussed. Specifically, the effect of ground losses was illustrated and discussed. When the travelling voltage and current waves are originated from lumped excitation sources located at a specific location along a transmission line (direct lightning strike), both the corona phenomenon and ground losses result in an attenuation and dispersion of propagating surges along transmission lines. However, when distributed sources representing the action of the electromagnetic field from a nearby lightning illuminating the line are present, ground losses and the corona phenomenon could result in important enhancement of the induced voltage magnitude. Finally, we reviewed the theory of electromagnetic field coupling to a buried cable. Solution methods in the frequency and the time domain were also presented. Examples of lightning-induced currents and comparison with experimental data were presented.SCI-STI-F
Lightning interaction with the ionosphere
No full textLightning discharges, including cloud-to-ground (CG) and intracloud (IC) lightning, are known to emit electromagnetic pulses (EMPs) in a wide frequency band ranging from few Hz up to hundreds MHz [1]. During the breakdown and ionization processes (mostly from leader processes and streamers), there are strong emissions in the HF (3-30 MHz) and VHF (30-300 MHz) bands. When high currents occur in previously ionized channels (mostly from return strokes and the active stage of cloud flashes), the most powerful emissions concentrate in the very low frequency (3-30 kHz, VLF) and low frequency (30-300 kHz, LF) bands [2]. Among them, the VLF/LF waves of lightning discharges can propagate long distances with low attenuation by reflection between the ground surface and the lower D-region ionosphere (60-90 km), namely the so-called earth-ionosphere waveguide (EIWG). In order to investigate the lightning EMPs interaction with the ionosphere, a number of models and methods have been developed in the literature, such as the wave-hop (ray theory) method [3-6], the waveguide mode theory [7-9], or numerical methods such as the finite-difference-time-domain (FDTD) method [10-17] and the full-wave finite element method (FEM) [18,19]. Previous studies indicate that the amplitude and phase perturbation for lightning VLF/LF signals have a complicated relationship with the ionospheric D region parameters. The propagation of lightning EMPs between the earth ground surface and the lower D region ionosphere can be affected by many factors, such as the propagation distances [10,14,20], the ground conductivity [14,20], the electron and neutral particle densities [13,21,22], the Earth curvature [23,24], the presence of the Earth's magnetic field [22,25-27], and the presence of mountainous terrain [24]. In this chapter, we will first introduce the propagation theory of lightning EMPs interaction with the ionosphere on the basis of the full-wave FDTD method. We will then investigate the propagation effect of lightning radiated electromagnetic (EM) fields in the EIWG by considering the effect of the Earth curvature, the effect of the ground conductivity, and the effect of different ionospheric profiles. Finally, we will present applications, including (1) propagation of narrow bipolar events (NBEs) at different distances, (2) lightning electromagnetic fields propagation over mountainous terrain, and (3) the optical emissions of lightning-induced transient luminous events in the nonlinear D-region ionosphere.SCI-STI-F
Una reflexión a partir de Sergei Leonidovich Rubinstein: Marcos de interacción y Campos constitutivos
No full textEl objetivo del presente texto es abordar la relación existente entre la filosofía y la psicología a partir de los postulados del autor soviético Sergei Leonidovich Rubinstein, pensador importante para el enfoque histórico-cultural de raíces marxistas-leninistas. A su vez, se plantea la posibilidad del desarrollo de nuevos conceptos (los Marcos y Campos), siguiendo algunos planteamientos del autor, pero con una clara diferencia: situarse en un ámbito ontológico-filosófico que permita un abordaje teórico de la psique como estructura y función, y mostrar que no se reduce a la práctica de los procesos psicológicos, es decir, que también se comunica y crea un diálogo esencial a partir de la filosofía.
Interaction of lightning-generated electromagnetic fields with overhead and underground cables
No full textSCI-STI-F
A Prony-Based Approach for Accelerating the Lightning Electromagnetic Fields Computation: Effect of the Soil Finite Conductivity
No full textThis work provides an approach for speeding up the evaluation of lightning ElectroMagnetic (EM) fields in the case of a finite soil conductivity. The soil conductivity is taken into account through the well-known Cooray-Rubinstein (CR) approximation, which corrects the radial term of the electric field. A comparative analysis with some of the existing methods reveals an excellent accuracy with a substantial improvement in the CPU performance.SCI-STI-F
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