1,721,005 research outputs found
Field-to-transmission line coupling models
No full textThis chapter presents the coupling of lightning electromagnetic fields to overhead and underground lines based on the transmission line approximation. The chapter starts with an introductory section in which the advantages and the drawbacks of three approaches, namely the quasi-static approach, the transmission line approach, and the antenna approach, are presented and discussed. The conditions of validity of the application of the transmission line approximation and its suitability for the case of lightning generated fields are also presented in that section
On the Stability of FDTD-Based Numerical Codes to Evaluate Lightning-Induced Overvoltages in Overhead Transmission Lines
No full textOne of the main issues that has to be faced when evaluating lightning-induced overvoltages on a realistic network configuration is to implement the algorithm that solves the field-to-line coupling problem into an electromagnetic simulator that is able to represent with a high level of detail all the power system components. On one hand, numerical stability conditions of the finite-difference time-domain schemes have been deeply investigated in the presence of boundary conditions known analytically; on the other hand, there is not so much literature on the situations in which such conditions are provided in a numerical way through an external electromagnetic simulator. The study reveals that the commonly used linear extrapolation of currents at the line extremities might rise to numerical instabilities. An efficient solution using the method of characteristics is presented and validated
Mitigation of Lightning-Induced Overvoltages Using Shield Wires: Application of the Response Surface Method
No full textLightning Performance of Overhead Power Distribution Lines in Urban Areas
No full textBuildings nearby urban overhead power lines are expected to reduce the number of direct strikes to the line conductors and also to attenuate the lightning electromagnetic pulse (LEMP) radiated by indirect lightning strokes. The statistical method described in IEEE Std. 1410 for the lightning performance assessment, as the other methods available in the literature, includes only the former effect. In order to take into account also the latter effect, in this paper, the LEMP attenuation due to the buildings is represented by means of specific weighting functions applied to the LEMP analytical expressions valid for open terrain. For both the cases of ideal and lossy ground, the parameters of the weighting functions are identified through the least-square minimization of the differences with the results provided by a finite-element method model that is assumed as reference for the configurations analyzed. The weighting functions can be used for lightning return stroke current waveform and distances between the line and the stroke location different from those used for their identification with reasonable accuracy. Finally, this paper compares the lightning performances of a power line evaluated with and without the presence of nearby buildings
Overvoltages caused by direct lightning strokes to a hybrid overhead line
Get PDFThis paper presents an analysis of the overvoltages caused by direct lightning strokes to a hybrid overhead line with 138 kV, 13.8 kV, and 220 V circuits. The primary focus is on medium voltage line overvoltages and their dependence on key parameters, including ground impedance, soil resistivity, stroke current front time, conductor characteristics, lightning channel impedance, insulator capacitance, conductors' sags, and tower surge impedance. Using specific models for the transmission tower and high-voltage insulators, validated through laboratory tests and EMTP simulations, critical currents are determined for varying soil resistivity and impulse impedances. The analysis confirms the line robust performance against stroke-induced backflashovers
Evaluation of the Mitigation Effect of Shield Wires on Lightning Induced Overvoltages in MV Distribution Systems using Statistical Analysis
No full textSCI-STI-F
Lightning induced overvoltages on overhead lines shielded by nearby buildings
No full textIn urban areas the presence of buildings is expected to reduce the amplitude of lightning induced voltages on overhead lines with respect to the case of open terrain. This paper presents a method for estimating such a reduction effect. For this purpose weighting functions are applied to the electrostatic, induction and radiation terms of the expressions adopted for the lightning electromagnetic field calculation assuming open terrain. The parameters of the weighting functions are identified by means of a least square fitting procedure using a finite element method model as benchmark for the field calculation. These functions are shown to be rather independent of the lightning return stroke current waveform and of the distance between the line and the stroke location. Although this paper presents only results obtained for the case of a single line, the method is conceived in order to be applicable for the lightning performance assessment of more complex power distribution networks
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Analysis of measured lightning-induced voltages on a matched experimental overhead line.
Get PDFEste trabalho apresenta uma análise de 64 tensões induzidas por descargas atmosféricas registradas em uma linha experimental não energizada de 2,7 km de comprimento, 10 m de altura, casada, localizada no campus da Universidade de São Paulo. As tensões registradas foram classificadas em quatro categorias e os parâmetros que caracterizam cada tipo, bem como suas distribuições estatísticas, são apresentados e discutidos. Cerca de 67% das tensões foram classificadas como unipolares (Tipo I) e, com exceção de um caso, todas apresentaram polaridade positiva. Cerca de 20% das tensões foram classificadas como Tipo II, cuja forma de onda é composta por dois semiciclos, sendo o primeiro de polaridade positiva. Cerca de 10% das tensões foram classificadas como Tipo III, cuja forma de onda também é composta por dois semiciclos, mas o primeiro com duração e magnitude muito menores. Apenas 3% foram classificadas como Tipo IV, cuja forma de onda possui três semiciclos e o valor de pico ocorre no terceiro, que possui polaridade negativa e maior duração. Os valores absolutos de pico das tensões registradas variaram amplamente, de cerca de 2 kV a 69 kV. Uma vez que as localizações dos pontos de incidência e as características dos canais e das correntes das descargas não eram conhecidas, uma comparação quantitativa entre as tensões medidas e calculadas não foi possível. No entanto, fez-se uma análise qualitativa, e as comparações entre os resultados medidos e calculados mostraram que as principais características das tensões registradas podem ser bem reproduzidas por simulações considerando condições típicas. Demonstra-se claramente que as tensões induzidas por descargas atmosféricas podem apresentar oscilações mesmo no caso de uma linha casada, sem para-raios, cabo guarda ou condutor neutro, o que certamente não é um resultado óbvio. As tensões induzidas medidas, mesmo as unipolares, diferiram significativamente da tensão de impulso atmosférico normalizada (impulso 1,2/50 s). O estudo permitiu uma melhor compreensão das características das tensões induzidas por descargas atmosféricas em uma linha simples e casada. A caracterização de tais surtos é um passo importante para uma estimativa mais precisa do desempenho de linhas de aéreas de distribuição, bem como para a seleção dos métodos de proteção mais eficientes frente a descargas atmosféricas.This Ph.D. dissertation presents an analysis of 64 lightning-induced voltages recorded on a 2.7 km long, 10 m high, matched, non-energized experimental line located on the University of São Paulo campus. The recorded voltages were classified into four categories and the parameters that characterize each type, as well as their statistical distributions, are presented and discussed. About 67% of the voltages were classified as unipolar (Type I) and, except for one case, all of them had positive polarity. About 20% of the voltages were classified as Type II, whose waveshape is composed of two semi-cycles, the first one of positive polarity. About 10% of the recorded voltages were classified as Type III, whose waveshape is also composed of two semi-cycles, but the first one which a much shorter duration and lower magnitude. Only 3% were classified as Type IV, whose waveshape has three semi-cycles and the maximum voltage value occurs in the third one, which has negative polarity and the longest duration. The maximum absolute voltage values of the recorded voltages varied widely, from about 2 kV to 69 kV. Since the stroke locations and the characteristics of the lightning channels and stroke currents were not known, a quantitative comparison between measured and calculated voltages is not possible. However, a qualitative analysis was made, and the comparisons between measured and calculated results shown that the main features of the recorded voltages can be well reproduced by simulations considering typical conditions. It is clearly demonstrated that lightning-induced voltages may present oscillations even in the case of a matched line without surge arresters, shield wire, or neutral conductor, which is certainly not an obvious result. The measured lightning-induced voltages, even the unipolar ones, differed significantly from the standard lightning impulse voltage (1.2/50 s). The study allowed a better understanding of the features of the lightning-induced voltages on a simple, matched line. The characterization of such surges is an important step for a more accurate estimation of the lightning performance of overhead distribution lines, as well as for the selection of the more efficient protection methods
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