Thesis (M.S.)--University of Florida, 2005. / Title from title page of source document. Document formatted into pages; contains 161 pages. Includes vita. Includes bibliographical references.

As descargas atmosféricas são reconhecidamente responsáveis por uma parcela expressiva das interrupções não programadas de fornecimento de energia em sistemas elétricos, contribuindo de forma significativa para a composição dos índices de qualidade de energia mesmo no caso de regiões com níveis ceráunicos moderados. No caso de sistemas de distribuição, grande parte dos problemas está relacionada às sobretensões induzidas por descargas próximas às linhas, as quais decorrem dos campos elétrico e magnético, associados à corrente que se propaga ao longo do canal da descarga. O conhecimento das características de tais campos é, portanto, fundamental para a determinação das sobretensões induzidas nas linhas aéreas de energia. Embora a importância do tema tenha propiciado nos últimos anos o desenvolvimento de um grande número de pesquisas a respeito dos campos eletromagnéticos e das tensões induzidas por descargas atmosféricas, na grande maioria dos trabalhos o solo é representado através de um plano condutor perfeito, portanto com condutividade infinita. Embora tal simplificação possa, em geral, ser considerada válida para a indução magnética e para o campo elétrico vertical, ela não é aplicável ao campo elétrico horizontal, em especial no caso de solos com alta resistividade. Este estudo visa avaliar o comportamento dos campos elétrico (vertical e horizontal) e indução magnética gerados por descargas atmosféricas nuvem-terra, levando em consideração os parâmetros da descarga (amplitude, forma de onda e velocidade de propagação da corrente) e os diferentes modelos para representação do canal da descarga. Além do caso de solo perfeitamente condutor, são consideradas situações mais realistas, isto é, verificando-se a influência, nos campos, de parâmetros como a resistividade e permissividade do solo. / The occurrence of lightning discharges causes a significant amount of unscheduled supply interruptions in overhead lines of electricity systems, contributing to decrease quality indicators of these systems, even in the case of regions with moderated ground flash density. Focusing on the distribution systems, great part of the problems are related to the induced voltages due to lightning discharges in the vicinity of overhead lines, which results from the electric and magnetic fields associated with the current propagation along the return stroke channel. The knowledge of the characteristics of lightning electromagnetic fields is, therefore, crutial for determining induced voltages on overhead lines. Although the importance of the assumption has propitiated in the last years the development of a great number of research concerning the lightning electromagnetic fields and induced voltages on overhead lines, in most of the studies the hypothesis of a perfect conducting ground is assumed. While such assumption can be considered valid for magnetic induction field and for the vertical component of the electric field, it doesn’t apply to the horizontal electric field, especially in the case of ground with high resistivity. The aim of this work is to present and to discuss the characteristics of the electric field (vertical and horizontal components) and magnetic induction generated by the cloud-to-ground lightning discharge, taking into account the lightning parameters (amplitude, waveform and propagation speed of the return stroke current) and the different return stroke models. Besides the case of perfect conducting ground, the influences of the ground permittivity and finite conductivity in the calculation of the electromagnetic fields are so considered.

As descargas atmosféricas são reconhecidamente responsáveis por uma parcela expressiva das interrupções não programadas de fornecimento de energia em sistemas elétricos, contribuindo de forma significativa para a composição dos índices de qualidade de energia mesmo no caso de regiões com níveis ceráunicos moderados. No caso de sistemas de distribuição, grande parte dos problemas está relacionada às sobretensões induzidas por descargas próximas às linhas, as quais decorrem dos campos elétrico e magnético, associados à corrente que se propaga ao longo do canal da descarga. O conhecimento das características de tais campos é, portanto, fundamental para a determinação das sobretensões induzidas nas linhas aéreas de energia. Embora a importância do tema tenha propiciado nos últimos anos o desenvolvimento de um grande número de pesquisas a respeito dos campos eletromagnéticos e das tensões induzidas por descargas atmosféricas, na grande maioria dos trabalhos o solo é representado através de um plano condutor perfeito, portanto com condutividade infinita. Embora tal simplificação possa, em geral, ser considerada válida para a indução magnética e para o campo elétrico vertical, ela não é aplicável ao campo elétrico horizontal, em especial no caso de solos com alta resistividade. Este estudo visa avaliar o comportamento dos campos elétrico (vertical e horizontal) e indução magnética gerados por descargas atmosféricas nuvem-terra, levando em consideração os parâmetros da descarga (amplitude, forma de onda e velocidade de propagação da corrente) e os diferentes modelos para representação do canal da descarga. Além do caso de solo perfeitamente condutor, são consideradas situações mais realistas, isto é, verificando-se a influência, nos campos, de parâmetros como a resistividade e permissividade do solo. / The occurrence of lightning discharges causes a significant amount of unscheduled supply interruptions in overhead lines of electricity systems, contributing to decrease quality indicators of these systems, even in the case of regions with moderated ground flash density. Focusing on the distribution systems, great part of the problems are related to the induced voltages due to lightning discharges in the vicinity of overhead lines, which results from the electric and magnetic fields associated with the current propagation along the return stroke channel. The knowledge of the characteristics of lightning electromagnetic fields is, therefore, crutial for determining induced voltages on overhead lines. Although the importance of the assumption has propitiated in the last years the development of a great number of research concerning the lightning electromagnetic fields and induced voltages on overhead lines, in most of the studies the hypothesis of a perfect conducting ground is assumed. While such assumption can be considered valid for magnetic induction field and for the vertical component of the electric field, it doesn’t apply to the horizontal electric field, especially in the case of ground with high resistivity. The aim of this work is to present and to discuss the characteristics of the electric field (vertical and horizontal components) and magnetic induction generated by the cloud-to-ground lightning discharge, taking into account the lightning parameters (amplitude, waveform and propagation speed of the return stroke current) and the different return stroke models. Besides the case of perfect conducting ground, the influences of the ground permittivity and finite conductivity in the calculation of the electromagnetic fields are so considered.

<p>The present society is highly dependant on complex electronics systems, which have a low damage threshold level. Therefore, there is a high risk of partial or total loss of the system’s electronics when they are exposed to a thunderstorm environment. This calls for a deep understanding on the mechanism related to the interaction of lightning generated electromagnetic fields with various large distributed/scattered systems. To accurately represent the interaction of lightning electromagnetic fields with electrical networks, it is necessary to have return stroke models capable to reproduce the electromagnetic field signatures generated by a lightning flash. Several models have been developed in the recent past to study the field-to-wire coupling mechanism. The most popular, simple and accurate among the available models is the Agrawal et al. model. On the other hand, ATP-EMTP is a well-known transient simulation package widely used by power engineers. This package has various built-in line models like Semlyen, Marti and Noda setups. There is a difficulty in applying the Agrawal et al. model with the built-in line models of ATP-EMTP, as the voltage source due to the horizontal component of electric field in Agrawal et al. model is in series with the line impedance and not in between two transmission line segments. Furthermore, when the electromagnetic field is propagating over a finite conducting ground plane, the soil will selectively attenuate the high frequency content of the electromagnetic field; causing a change in the field wave shape. A finite conducting ground will also produce a horizontal field component at the ground level. Several approximations are available in the literature to obtain the horizontal electric field; namely the wave-tilt and the Cooray-Rubinstein approximation. Consequently, it is important to investigate the change on the induced voltage signature when the power line is located over a finitely conducting ground. Additionally, to provide protection from lightning induced transients it is necessary to use Surge Protective Devices (SPDs) capable of diverting the incoming transients and provide protection level necessary to avoid damage in the equipment. However, standard test procedures of the SPDs do not take into account sub-microsecond structure of the transients. Therefore, to provide the required protection level to sensitive equipments connected to the low voltage power network, it is essential to understand the response of SPDs subjected to high current derivative impulses. This thesis is aimed to investigate the research problems as addressed above. Special attention will be given to a new proposed return stroke model, a simple circuit approach for efficient implementation of Agrawal et al. model using ATP-EMTP, the effect of the soil conductivity on the lightning induced overvoltage signatures and the response of surge protective devices subjected to high current derivative impulses.</p>

The present society is highly dependant on complex electronics systems, which have a low damage threshold level. Therefore, there is a high risk of partial or total loss of the system’s electronics when they are exposed to a thunderstorm environment. This calls for a deep understanding on the mechanism related to the interaction of lightning generated electromagnetic fields with various large distributed/scattered systems. To accurately represent the interaction of lightning electromagnetic fields with electrical networks, it is necessary to have return stroke models capable to reproduce the electromagnetic field signatures generated by a lightning flash. Several models have been developed in the recent past to study the field-to-wire coupling mechanism. The most popular, simple and accurate among the available models is the Agrawal et al. model. On the other hand, ATP-EMTP is a well-known transient simulation package widely used by power engineers. This package has various built-in line models like Semlyen, Marti and Noda setups. There is a difficulty in applying the Agrawal et al. model with the built-in line models of ATP-EMTP, as the voltage source due to the horizontal component of electric field in Agrawal et al. model is in series with the line impedance and not in between two transmission line segments. Furthermore, when the electromagnetic field is propagating over a finite conducting ground plane, the soil will selectively attenuate the high frequency content of the electromagnetic field; causing a change in the field wave shape. A finite conducting ground will also produce a horizontal field component at the ground level. Several approximations are available in the literature to obtain the horizontal electric field; namely the wave-tilt and the Cooray-Rubinstein approximation. Consequently, it is important to investigate the change on the induced voltage signature when the power line is located over a finitely conducting ground. Additionally, to provide protection from lightning induced transients it is necessary to use Surge Protective Devices (SPDs) capable of diverting the incoming transients and provide protection level necessary to avoid damage in the equipment. However, standard test procedures of the SPDs do not take into account sub-microsecond structure of the transients. Therefore, to provide the required protection level to sensitive equipments connected to the low voltage power network, it is essential to understand the response of SPDs subjected to high current derivative impulses. This thesis is aimed to investigate the research problems as addressed above. Special attention will be given to a new proposed return stroke model, a simple circuit approach for efficient implementation of Agrawal et al. model using ATP-EMTP, the effect of the soil conductivity on the lightning induced overvoltage signatures and the response of surge protective devices subjected to high current derivative impulses.