The rapid expansion of wind power generation has brought problems involving lightning strikes to the fore. Many such incidents have damaged not only the wind turbine that was actually struck but also other turbines that were not, a phenomenon that has yet to be fully explained. In this paper, the authors present a case study using a wind farm model with multiple wind turbines connected to a power system. The aim is to clarify the influence of the grounding system on surge propagation from a wind turbine that has been struck to others which have not, during a winter lightning strike. Sensitivity analyses show that the surge propagated to nearby wind turbines can sometimes become large, depending on the conditions of the grounding system, and result in the burnout of surge arresters in turbines that have not been struck, especially during winter lightning strikes.