Energies 2023, 16, 1111. https://doi.org/10.3390/en16031111 www.mdpi.com/journal/energies Article Mitigation of Insulator Lightning-Induced Voltages by Installing Parallel Low-Voltage Surge Arresters André M. de Morais *, Rodrigo M. S. de Oliveira and Marcus V. A. Nunes Institute of Technology, Federal University of Pará, Belém 66075-110, Brazil * Correspondence: andremmorais@ufpa.br; Tel.: +55-091-98707-0746 Abstract: In this paper, we propose a mitigation method for reducing lightning-induced insulator voltages based on the installation of low-voltage surge arresters aligned parallelly to the insulator. The three-dimensional finite-difference time-domain (FDTD) method is applied to numerically model a real surge arrester residual voltage evaluation system. The application of a transient current pulse, typical of lightning discharges, is considered in our numerical model. We considered cases with one or two surge arresters installed per phase, in three different geometric and parametric configurations for installing distribution surge arresters. In addition to the Kirchhoff current division, which reduces both the absorbed energy and the thermal stress, the results associated with the installation of two surge arresters parallelly aligned to the insulator show that the interaction of magnetic fields generated by the surge arresters’ currents can produce an additional strong reduction in lightning-induced voltage over the insulator, as presented in this paper. Conditions for maximum voltage reduction are also identified. A brief cost-effectiveness analysis is also provided. Keywords: lightning discharges; parallel surge arresters; interaction of magnetic fields; mitigation of insulator lightning-induced voltages 1. Introduction Lightning discharges produce strong transient electromagnetic fields associated with fast high-current flows (tens of kiloamperes during a few microseconds, in general). In Brazil alone, the occurrence of 50 to 100 million lightning events is estimated per year [1,2], which is the main cause of service interruptions linked to electric power distribution overhead system issues [3–5]. In some Brazilian regions, for instance, 30% to 40% of unavailability events of such distribution systems are caused by lightning occurrences [6,7] and approximately 47% of power transformers are damaged by atmospheric discharges [8], leading to high financial losses to power companies and various damage to society due to electric damage to equipment and interruption in electric power supply. The proposal of efficient remedial measures applied to power distribution networks is not a simple issue due to the associated complex physics. Therefore, the use of adequate numerical methods and computational tools for modelling the physics of such networks is necessary. The Electromagnetic Transient Program (EMTP) [9], which is based on circuit and transmission line theories for calculating overvoltages and overcurrents in electric power distribution networks, has been frequently employed [10–13]. However, over the past few years, the use of full-wave numerical approaches for calculating and analyzing transient electromagnetic fields over distribution networks has produced physically complete solutions and, consequently, comprehensive conclusions and new possibilities to solve engineering problems. Among the methods for numerically solving Maxwell’s equations, the finite-difference time-domain (FDTD) method [14,15] has been widely adopted for analyzing transient fields over distribution networks, since it enables modelling complex three-dimensional structures, such as grounding structures [16–19], Citation: de Morais, A.M.; de Oliveira, R.M.S.; Nunes, M.V.A. Mitigation of Insulator Lightning- Induced Voltages by Installing Par- allel Low-Voltage Surge Arresters. Energies 2023, 16, 1111. https://doi.org/10.3390/en16031111 Academic Editor: Salvatore Celozzi and Massimo Marzinotto Received: 18 December 2022 Revised: 12 January 2023 Accepted: 15 January 2023 Published: 19 January 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/license s/by/4.0/).