Assessment of wind turbine transient overvoltages when struck by lightning: Experimental and analytical study

Abstract

This paper is aimed at presenting a numerical method for calculating the transient overvoltage across a wind turbine (WT) struck by lightning. The resulting overvoltage is determined at different points along the WT body using the proposed numerical method. The lightning strike has been simulated by injecting a current impulse to the tested WT. The equivalent circuits of WT components and the mathematical formulas to evaluate the circuit's parameters are presented. This makes it possible to develop -equivalent RLC networks representing the WT components to write the nodal equations at each discrete time instant. MATLAB software package is used to solve the nodal equations and determine the transient behaviour of the WT. In the laboratory, a high impulse voltage is applied on a small-scale WT to corroborate the proposed method. The calculated overvoltage temporal variations are in good agreement with those measured at different positions along the WT for various grounding resistance values, demonstrating the validity of the proposed method. Further validation is also made by comparing the present simulation with that using PSCAD/EMTDC software package. The overvoltage values increase with the rise of the grounding resistance value. The obtained results are useful for designing WT lightning protection systems.