One of the main causes of damages for wind-turbine power plants is lightning. Direct and indirect events, indeed, can produce damages and malfunctions of electrical and mechanical components. Concerning mechanical components, blades and bearings are the most involved parts. In particular, lightning damages to main-shaft bearings can result in high costs of maintenance, due to the inherent burden in the replacement of these components. The paper focuses on the modeling of wind-turbine main-shaft bearings. Two models are presented and experimentally validated: one numerical and one analytical, both conceived in a way to make the calculation of the bearing electrical impedance possible. The paper shows how these models are helpful for the design of wind-turbines lightning protection systems (LPSs). In this respect, it illustrates the criteria for the design of such an LPS and assesses the validity of design solutions by means of experimental tests. © 2010 IEEE.