Frequency-dependent modeling of grounding system for wind turbine lightning transient studies

An efficient technique is proposed to incorporate the frequency-dependent characteristic of wind turbine grounding system in ElectroMagnetic Transient Program (EMTP) 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-moments solutions of the governing Maxwell´s equations. To avoid the inevitable time-consuming computation time required for the wide-band lightning frequency spectrum, the number of frequency calculation points is reduced by a model-based parameter estimation approach. The resultant frequency response of the grounding system is then incorporated in EMTP, using an appropriate time-domain state-space model. The proposed technique is utilized to study the effects of frequency-dependent grounding system on lightning overvoltages in a typical wind power plant.