Lightning is one of the main causes of damage to wind turbines. The continuous increase in the wind turbine heights makes these structures even more vulnerable against lightning. As a result, the design of proper lightning protection system is of high importance. The paper deals with the determination of the transient impedance of wind turbines via different approaches. The analysis is carried out in the frequency domain using a transmission line model and a full wave approach via NEC4 commercial simulation tool. First, a simple tower configuration is considered and then a more complex case including tower with blades is considered. Coupling between blades and tower are taken into account by means of the full wave approach. To evaluate coupling effects, different angles of blades are considered. The approximation of a perfectly conducting (PEC) ground is assumed.