Análise das sobretensões decorrentes de descargas atmosféricas em estruturas de turbinas eólicas offshore com fundação do tipo monopile

Abstract

This work presents a detailed electromagnetic model of offshore wind turbines whose monopile foundation acts as the grounding system, aiming to evaluate transient overvoltages resulting from direct lightning strikes (upward and downward), based on real data from Morro do Cachimbo and Monte San Salvatore. Protecting offshore wind turbines against lightning strikes is a major technical challenge to ensure safe and continuous operation in marine environments. Due to their height and isolation, such structures are highly vulnerable to severe transient overvoltages. The developed model consists of (i) a multicomponent representation of the return stroke current using Heidler functions fitted to measured lightning currents, (ii) a modeling of blades and tower through distributed transmission-line segments whose electrical parameters vary according to the actual geometry of the structure, and (iii) a grounding impedance of the monopile foundation calculated using classical equations and subsequently fitted via Vector Fitting, and then represented by an equivalent lumped-element network in ATP/ATPDraw. The Ground Potential Rise (GPR), structural overvoltages, and the sensitivity to seawater resistivity and lightning-channel modeling are systematically assessed. The main results show: (a) strong dependence of the GPR on seawater resistivity and the representation of the lightning channel; (b) high dielectric stress on glass-fiber-reinforced polymer (GFRP) blades under typical lightning scenarios; and (c) significant waveform changes when overhead components are included. The proposed modeling approach provides meaningful contributions toward improving the design of more effective lightning-protection systems in offshore wind farms.