Contribuição relativa à influência do efeito corona no desempenho de linhas de transmissão frente a descargas atmosféricas

Abstract

Direct lightning strikes in transmission lines are responsible for major part of transmission lines outages in electric systems. The assessment of lightning performance of transmission lines is extremely important for providing means to perform the necessary interventions on the analyzed line. The incidence of high amplitude discharge currents on the shield wire leads to an increase in the electric field surrounding the conductor, leading to an air ionization around it, this nonlinear phenomenon being called corona effect. In this work, this effect is investigated in transmission lines submitted to high amplitude discharge currents and is analyzed how it influences in the insulator overvoltage and, consequently, in the lightning performance of the line considering the backflashover phenomenon. In this work, corona effect is modeled considering a radial expansion of the radius conductor. Simulations were carried out using a computational electromagnetic model in frequency domain, HEM (Hybrid Electromagnetic Model), for overvoltage calculations in the transmission line and the DE method (Disruptive Effect Method) for evaluation of flashover occurrence at transmission line insulator. The obtained results showed that corona effect representation leaded to a decrease of the overvoltage along the shield wire and an increase of overvoltage at phase conductor. Besides that, it was observed a decrease of the overvoltage developed across the insulator string, leading to the improvement of the lightning performance of the line. However, that improvement was less important than commonly presented in the literature, showing that the effect promoted by tower-footing grounding is the most relevant factor in the establishment of the current that flows through the tower, defining the insulator overvoltage.