Análise técnico-econômica de alternativas convencionais e não-convencionais para melhoria de desempenho de linhas de transmissão frente a descargas atmosféricas

Abstract

Most of the unscheduled transmission lines (TLs) outages occur due to direct lightning strikes to the electrical system. These outages promote the interruption in the energy supply, resulting in losses for electric power companies and their consumers. In this way, the analysis of the lightning performance of TLs is a very relevant procedure for electrical engineering, and that can provide elements for interventions to be made in TLs in order to adequate their outage rate to performance index stipulated by regulatory agencies. This work aimed to evaluate conventional and unconventional alternatives for improving the lightning performance of transmission lines considering the development of a technical-economic analysis for typical transmission lines of 138 kV, 230 kV and 500 kV. The work was developed using the techniques of increasing the length of counterpoise wires and the installation of underbuilt wires. Systematic computational simulations were performed using the Hybrid Electromagnetic Model (HEM) to calculate the resulting overvoltages across TL insulator strings and the Disruptive Effect (DE) method to assess the occurrence of backflashover. The obtained results provided the establishment of references that denote the impact of each of the improvement techniques on the performance of transmission lines. For 138 kV, 230 kV, and 500 kV transmission lines, respectively, the installation of one underbuilt wire resulted in the probability of backflashover occurrence reduction up to 84%, 81%, and 88%. The use of two underbuilt wires resulted in decreases of the order of 95%, 94%, and 94%. In terms of the improvement of the lightning performance, the effect of using one underbuilt wire corresponds, approximately, to decrease the tower-footing grounding impulse impedance to its half value, for the 138 kV TL, and to 55% of its value, for 230 kV and 500 kV TLs. The sensitivity analyzes considered different heights for the installation of the underbuilt wires and the evaluation of the effects of current divergence and electromagnetic coupling to establish the lightning performance improvement, indicating in which conditions they become more relevant. The technical-economic analysis considered the ANEEL Reference Price Database to determine the economic viability of the improvement techniques for different soil resistivity values. The results indicated that the underbuilt wire technique is an economically viable solution for high resistivity soils.