Analysis of the lightning attractive radius of power transmission lines through the use of a physically-oriented model

Models of different degrees of complexity are found in the literature for the estimation of lightning striking distances and attractive radius of objects and structures. However, besides the oversimplifications of the physical nature of the lightning discharge on which most of them are based, till recently the tridimensional structure configuration could not be considered. This is an important limitation, as edges and other details of the object affect the electric field and, consequently, the upward leader initiation. Within this context, the Self-consistent leader initiation and propagation model (SLIM) proposed by Becerra and Cooray is state-of-the-art leader inception and propagation leader model based on the physics of leader discharges which enables the tridimensional geometry of the structure to be taken into account. In this paper, the model is used for estimating the striking distance and attractive radius of power transmission lines. The results are compared with those obtained from the electrogeometric and Eriksson's models. © 2003-2012 IEEE.

Protecção contra descargas atmosféricas: aplicação informática de identificação das vulnerabilidades das edificações e de apoio à concepção da protecção

A concepção de instalações eléctricas deve garantir condições de segurança para as pessoas e equipamentos. Para tal é exigida, quer por força de regulamentação ou de normalização, a instalação de dispositivos que garantam a detecção e a protecção contra os defeitos mais comuns nas instalações eléctricas como, por exemplo, as sobreintensidades e as sobretensões. Susceptíveis de criar sobretensões perigosas nas instalações eléctricas, as descargas atmosféricas podem ainda causar danos estruturais elevados, o que, em algumas actividades económicas, torna fundamental a implementação de medidas de protecção contra este fenómeno natural. A protecção contra descargas atmosféricas directas consiste em identificar as vulnerabilidades das estruturas e, nesses locais, implementar dispositivos de captura, direccionamento e escoamento da descarga atmosférica à terra, em condições de segurança. O presente trabalho, desenvolvido no âmbito da dissertação de Mestrado em Engenharia Electrotécnica, visa desenvolver e implementar uma ferramenta computacional, baseada em programas de desenho assistido por computador (CAD) de utilização corrente na área de projecto de arquitectura e de engenharia, que permita, no âmbito de normas internacionais, a análise e implementação de sistemas de protecção em edifícios contra descargas atmosféricas de uma forma rápida e expedita. Baseado num programa CAD 3D, que permite a modelização tridimensional das estruturas a proteger, a ferramenta desenvolvida tentará identificar as suas vulnerabilidades das estruturas às descargas atmosféricas directas, com o intuito de implementar as medidas de protecção mais adequadas do ponto de vista técnico económico. Prevê-se que a ferramenta resultante deste estudo, o Simulador do Modelo Electrogeométrico (SIMODEL), possibilite aos projectistas e particularmente aos alunos das unidades curriculares na área do projecto de instalações eléctricas da Área Departamental de Engenharia de Sistemas e Potencia e Automação (ADESPA) do ISEL, estudar e implementar sistemas de protecção contra descargas atmosféricas (SPDA) baseados na normalização internacional do CENELEC e da IEC, nomeadamente as normas da série 62305.

An overview of Earth's global electric circuit and atmospheric conductivity

The Earth’s global atmospheric electric circuit depends on the upper and lower atmospheric boundaries formed by the ionosphere and the planetary surface. Thunderstorms and electrified rain clouds drive a DC current (∼1 kA) around the circuit, with the current carried by molecular cluster ions; lightning phenomena drive the AC global circuit. The Earth’s near-surface conductivity ranges from 10−7 S m−1 (for poorly conducting rocks) to 10−2 S m−1 (for clay or wet limestone), with a mean value of 3.2 S m−1 for the ocean. Air conductivity inside a thundercloud, and in fair weather regions, depends on location (especially geomagnetic latitude), aerosol pollution and height, and varies from ∼10−14 S m−1 just above the surface to 10−7 S m−1 in the ionosphere at ∼80 km altitude. Ionospheric conductivity is a tensor quantity due to the geomagnetic field, and is determined by parameters such as electron density and electron–neutral particle collision frequency. In the current source regions, point discharge (coronal) currents play an important role below electrified clouds; the solar wind-magnetosphere dynamo and the unipolar dynamo due to the terrestrial rotating dipole moment also apply atmospheric potential differences. Detailed measurements made near the Earth’s surface show that Ohm’s law relates the vertical electric field and current density to air conductivity. Stratospheric balloon measurements launched from Antarctica confirm that the downward current density is ∼1 pA m−2 under fair weather conditions. Fortuitously, a Solar Energetic Particle (SEP) event arrived at Earth during one such balloon flight, changing the observed atmospheric conductivity and electric fields markedly. Recent modelling considers lightning discharge effects on the ionosphere’s electric potential (∼+250 kV with respect to the Earth’s surface) and hence on the fair weather potential gradient (typically ∼130 V m−1 close to the Earth’s surface. We conclude that cloud-to-ground (CG) lightning discharges make only a small contribution to the ionospheric potential, and that sprites (namely, upward lightning above energetic thunderstorms) only affect the global circuit in a miniscule way. We also investigate the effects of mesoscale convective systems on the global circuit.

An overview of Earth’s global electric circuit and atmospheric conductivity

The Earth’s global atmospheric electric circuit depends on the upper and lower atmospheric boundaries formed by the ionosphere and the planetary surface. Thunderstorms and electrified rain clouds drive a DC current (∼1 kA) around the circuit, with the current carried by molecular cluster ions; lightning phenomena drive the AC global circuit. The Earth’s near-surface conductivity ranges from 10−7 S m−1 (for poorly conducting rocks) to 10−2 S m−1 (for clay or wet limestone), with a mean value of 3.2 S m−1 for the ocean. Air conductivity inside a thundercloud, and in fair weather regions, depends on location (especially geomagnetic latitude), aerosol pollution and height, and varies from ∼10−14 S m−1 just above the surface to 10−7 S m−1 in the ionosphere at ∼80 km altitude. Ionospheric conductivity is a tensor quantity due to the geomagnetic field, and is determined by parameters such as electron density and electron–neutral particle collision frequency. In the current source regions, point discharge (coronal) currents play an important role below electrified clouds; the solar wind-magnetosphere dynamo and the unipolar dynamo due to the terrestrial rotating dipole moment also apply atmospheric potential differences. Detailed measurements made near the Earth’s surface show that Ohm’s law relates the vertical electric field and current density to air conductivity. Stratospheric balloon measurements launched from Antarctica confirm that the downward current density is ∼1 pA m−2 under fair weather conditions. Fortuitously, a Solar Energetic Particle (SEP) event arrived at Earth during one such balloon flight, changing the observed atmospheric conductivity and electric fields markedly. Recent modelling considers lightning discharge effects on the ionosphere’s electric potential (∼+250 kV with respect to the Earth’s surface) and hence on the fair weather potential gradient (typically ∼130 V m−1 close to the Earth’s surface. We conclude that cloud-to-ground (CG) lightning discharges make only a small contribution to the ionospheric potential, and that sprites (namely, upward lightning above energetic thunderstorms) only affect the global circuit in a miniscule way. We also investigate the effects of mesoscale convective systems on the global circuit.

Avaliação da suscetibilidade eletromagnética dos cabos metálicos dos sistemas de supervisão, proteção, comunicação e controle de subestações de alta tensão

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Pós-processamento de formas de ondas oriundas de descargas atmosféricas no Centro de Estudos de Descargas Atmosféricas e Alta Tensão (CENDAT) – IEE/USP

Atmospheric Discharges are responsible for several lost in the electrical system therefore it´s done studies to find ways to reduce the problem caused by discharges. This branch of engineering is necessary the gathering, stock and analysis of large quantity of data to validate or refuse the many studies produced about it The CENDAT proposed a project to collect data on induced voltages in distribution lines and current waveform of the lightning, but a difficulty that arose was the accumulation of data due to lack of manpower available to catalog all the data collected. Thinking in this difficulty, the engineer Acacio Silva Neto CENDAT´s researcher with trainees began to develop a program to solve this problem. This work keeps the development of this program in order to solve the problem of accumulation of data

Lightning-induced intensification of the ionospheric sporadic E layer

A connection between thunderstorms and the ionosphere has been hypothesized since the mid-1920s(1). Several mechanisms have been proposed to explain this connection(2-7), and evidence from modelling(8) as well as various types of measurements(9-14) demonstrate that lightning can interact with the lower ionosphere. It has been proposed, on the basis of a few observed events(15), that the ionospheric 'sporadic E' layer - transient, localized patches of relatively high electron density in the mid-ionosphere E layer, which significantly affect radio-wave propagation - can be modulated by thunderstorms, but a more formal statistical analysis is still needed. Here we identify a statistically significant intensification and descent in altitude of the mid-latitude sporadic E layer directly above thunderstorms. Because no ionospheric response to low-pressure systems without lightning is detected, we conclude that this localized intensification of the sporadic E layer can be attributed to lightning. We suggest that the co-location of lightning and ionospheric enhancement can be explained by either vertically propagating gravity waves that transfer energy from the site of lightning into the ionosphere, or vertical electrical discharge, or by a combination of these two mechanisms.

A computational tool to assist the analysis of the transformer behavior related to lightning

This paper proposes the application of computational intelligence techniques to assist complex problems concerning lightning in transformers. In order to estimate the currents related to lightning in a transformer, a neural tool is presented. ATP has generated the training vectors. The input variables used in Artificial Neural Networks (ANN) were the wave front time, the wave tail time, the voltage variation rate and the output variable is the maximum current in the secondary of the transformer. These parameters can define the behavior and severity of lightning. Based on these concepts and from the results obtained, it can be verified that the overvoltages at the secondary of transformer are also affected by the discharge waveform in a similar way to the primary side. By using the tool developed, the high voltage process in the distribution transformers can be mapped and estimated with more precision aiding the transformer project process, minimizing empirics and evaluation errors, and contributing to minimize the failure rate of transformers. (C) 2011 Elsevier Ltd. All rights reserved.

High-speed video observations of positive ground flashes produced by intracloud lightning

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A neural approach to evaluate the effect of lightning in power transformers

This paper proposes the application of computational intelligence techniques to assist complex problems concerning lightning in transformers. In order to estimate the currents related to lightning in a transformer, a neural tool is presented. ATP has generated the training vectors. The input variables used in Artificial Neural Networks (ANN) were the wave front time, the wave tail time, the voltage variation rate and the output variable is the maximum current in the secondary of the transformer. These parameters can define the behavior and severity of lightning. Based on these concepts and from the results obtained, it can be verified that the overvoltages at the secondary of transformer are also affected by the discharge waveform in a similar way to the primary side. By using the tool developed, the high voltage process in the distribution transformers can be mapped and estimated with more precision aiding the transformer project process, minimizing empirics and evaluation errors, and contributing to minimize the failure rate of transformers. © 2009 The Berkeley Electronic Press. All rights reserved.

The cloud–ionosphere discharge: A newly observed thunderstorm phenomenon

This paper deals with a luminous electric discharge that forms in the mesospheric region between thundercloud tops and the ionosphere at 90-km altitude. These cloud–ionosphere discharges (CIs), following visual reports dating back to the 19th century, were finally imaged by a low-light TV camera as part of the “SKYFLASH” program at the University of Minnesota in 1989. Many observations were made by various groups in the period 1993–1996. The characteristics of CIs are that they have a wide range of sizes from a few kilometers up to 50 km horizontally; they extend from 40 km to nearly 90 km vertically, with an intense region near 60–70 km and streamers extending down toward cloud tops; the CIs are partly or entirely composed of vertical luminous filaments of kilometer size. The predominate color is red. The TV images show that the CIs usually have a duration less than one TV field (16.7 ms), but higher-speed photometric measurements show that they last about 3 ms, and are delayed 3 ms after an initiating cloud–ground lightning stroke; 95% of these initiating strokes are found to be “positive”—i.e., carry positive charges from clouds to ground. The preference for positive initiating strokes is not understood. Theories of the formation of CIs are briefly reviewed.

Effects of drill cuttings discharge on meiofauna communities of a shelf break site in the southwest Atlantic

The present study investigates the effects of drill cutting discharges on the structure of meiofauna communities in an area of the shelf break at Campos Basin, Southeast Brazil. Drilling activities were operated, in a first phase, with water-based fluid and, in a second phase, with synthetic fluid paraffin-based (NAF-III). A total of 135 samples taken at a pre-drilling situation (MS1) and two post-drilling moments (MS2 and MS3-3 and 22 months post-drilling, respectively) were analyzed. Effects on meiofauna were dependent on two main factors: 1-the impact received during drilling operation, if water-based or synthetic/water-based drilling fluid and 2-the background state, if it already presented signs of previous drilling activities or not. Based on univariate and multivariate analysis, there were evidences that the most affected area after drilling was those under the influence of synthetic-based fluid and that already had signs of previous drillings activities. The region impacted only by water-based fluid was less affected and the only one that completely recovered after 22 months. Nematodes and copepods had different responses to the impact. While copepods flourish in the impacted area and recovered 22 months after drilling, nematodes were adversely affected shortly after drilling and the community structure only recovered where hydrocarbons had been depleted.

Discharge-calcium concentration relationships in streams of the Amazon and Cerrado of Brazil: soil or land use controlled

Stream discharge-concentration relationships are indicators of terrestrial ecosystem function. Throughout the Amazon and Cerrado regions of Brazil rapid changes in land use and land cover may be altering these hydrochemical relationships. The current analysis focuses on factors controlling the discharge-calcium (Ca) concentration relationship since previous research in these regions has demonstrated both positive and negative slopes in linear log(10)discharge-log(10)Ca concentration regressions. The objective of the current study was to evaluate factors controlling stream discharge-Ca concentration relationships including year, season, stream order, vegetation cover, land use, and soil classification. It was hypothesized that land use and soil class are the most critical attributes controlling discharge-Ca concentration relationships. A multilevel, linear regression approach was utilized with data from 28 streams throughout Brazil. These streams come from three distinct regions and varied broadly in watershed size (< 1 to > 10(6) ha) and discharge (10(-5.7)-10(3.2) m(3) s(-1)). Linear regressions of log(10)Ca versus log(10)discharge in 13 streams have a preponderance of negative slopes with only two streams having significant positive slopes. An ANOVA decomposition suggests the effect of discharge on Ca concentration is large but variable. Vegetation cover, which incorporates aspects of land use, explains the largest proportion of the variance in the effect of discharge on Ca followed by season and year. In contrast, stream order, land use, and soil class explain most of the variation in stream Ca concentration. In the current data set, soil class, which is related to lithology, has an important effect on Ca concentration but land use, likely through its effect on runoff concentration and hydrology, has a greater effect on discharge-concentration relationships.

Friction loss correction in flowing well discharge tests

Artesian confined aquifers do not need pumping energy, and water from the aquifer flows naturally at the wellhead. This study proposes correcting the method for analyzing flowing well tests presented by Jacob and Lohman (1952) by considering the head losses due to friction in the well casing. The application of the proposed correction allowed the determination of a transmissivity (T = 411 m(2)/d) and storage coefficient (S = 3 x 10(-4)) which appear to be representative for the confined Guarani Aquifer in the study area. Ignoring the correction due to head losses in the well casing, the error in transmissivity evaluation is about 18%. For the storage coefficient the error is of 5 orders of magnitude, resulting in physically unacceptable value. The effect of the proposed correction on the calculated radius of the cone of depression and corresponding well interference is also discussed.

Lightning-Induced Voltages on Overhead Lines-Application of the Extended Rusck Model

Lightning-induced overvoltages have a considerable impact on the power quality of overhead distribution and telecommunications systems, and various models have been developed for the computation of the electromagnetic transients caused by indirect strokes. The most adequate has been shown to be the one proposed by Agrawal et al.; the Rusck model can be visualized as a particular case, as both models are equivalent when the lightning channel is perpendicular to the ground plane. In this paper, an extension of the Rusck model that enables the calculation of lightning-induced transients considering flashes to nearby elevated structures and realistic line configurations is tested against data obtained from both natural lightning and scale model experiments. The latter, performed under controlled conditions, can be used also to verify the validity of other coupling models and relevant codes. The so-called Extended Rusck Model, which is shown to be sufficiently accurate, is applied to the analysis of lightning-induced voltages on lines with a shield wire and/or surge arresters. The investigation conducted indicates that the ratio between the peak values of the voltages induced by typical first and subsequent strokes can be either greater or smaller than the unity, depending on the line configuration.