Determinação e modelagem da impedância de surto de torres de linhas de transmissão e seus efeitos no estudo de sobretensões atmosféricas

Abstract

This thesis brings together concepts and analyzes that base and favor the development of alternatives for the determination of the towers surge impedance through computational models. The lightning strikes in the transmission lines and their effects on the tower surge impedance, can favor the formation of a permanent electric arc between tower and line wires, characterizing the backflashover. This work proposes a methodology for determination of the tower surge impedance, in order to obtain an improvement in the accuracy of this parameter. Therefore, this thesis proposes the creation of three-dimensional computational models, to which the Finite Element Method (FEM) is applied as a tool for the analysis of the electromagnetic fields involved in the phenomenon. In general, this methodology consists of the application of the Finite Element Method (FEM) in three-dimensional computational models of transmission towers. In this way, the FEM provides the quantitative characteristics of the electromagnetic fields that surround the tower. An analytical work is then applied to the FEM results, in order to obtain the tower surge impedance. The FEM provides the use of new potentialities, such as the determination of the surge impedance for different types of towers, without making simplifications. Based on a measurement data base, investigative work is carried out to verify the qualitative and quantitative aspects of the models described. From comparisons between results of measurements, existing and proposal methods, an evaluation of the techniques are developed in order to expose their main characteristics. In addition, in order to study the influence of surge impedance on the tower voltages, general aspects related to the electrical representation of transmission towers are discussed, culminating in the use of a robust model for transient analysis through the EMTP/ATP software. Thus, from the imposition of surge currents on the electric tower model will produce voltages in the structure. These results will also be compared to experimental data in order to verify the reliability of the electric model. In addition, analyzes will be presented on the influence of the variation of parameters directly related to the phenomenon, to verify its impacts on the voltages originated in the tower due to surge currents.