Wind turbine grounding system frequency-dependent modeling for lightning transient studies

This paper presents an accurate modeling technique for inclusion of the frequency-dependent characteristics of a wind turbine grounding system into time-domain codes for lightning transient studies. In this technique, first, the frequency response of grounding system is determined using an electromagnetic approach based on the method-of-moment solutions of the governing Maxwell´s equations. A time-domain state-space model of the resultant frequency response of the grounding system is then obtained by making use of the vector fitting technique. The proposed technique is used to analyze the effects of wide-band modeling of grounding system on predicted lightning transient overvoltages in a typical wind power plant. It is shown that the predicted overvoltage by the conventional resistive model of the grounding system gives an underestimation of those obtained accurately using the proposed model.