Modelagem do efeito corona em linhas de transmissão utilizando o método FDTD para o estudo de sobretensões transitórias

Abstract

This work presents a study about the modeling of corona for the simulation of electromagnetic transients in transmission lines with frequency-dependent losses, using the Finite Difference Time Domain (FDTD) technique in the solution of telegrapher’s equations. Initially, a literature review is carried out in which the corona fundamentals are discussed together with a survey of formulations for the calculation of the critical voltage and models for the corona representation in the simulation of electromagnetic transients. Then, the rigorous solution of the transmission line equations with frequency-dependent losses is presented using the FDTD technique. It is demonstrated how this technique can incorporate, in a natural and accurate way, the corona effect modeling. The methodology has the ability of representing frequency-dependent losses and the nonlinear nature of corona directly in its formulation. The developed model, which in this work is restricted to the case of single-phase lines, is implemented in Matlab; its validation is carried out based on records of measurements and simulations available in the literature. Finally, based on the developed model, a simplified case study is developed on the impact of corona on lightning overvoltages on a line whose geometry is used in High Voltage Direct Current (HVDC) transmission systems. It is verified that the corona effect modifies the waveform of the lightning overvoltage incident at a certain point on the line, reducing the amplitude and increasing the front time as it propagates. This result indicates that the consideration of corona in insulation coordination studies would lead to less severe overvoltages, providing benefits for the protection of the equipment installed in substations.