In this paper a mixed frequency and time domain approach is proposed for the analysis of the dynamics of multiconductor power lines excited by indirect lightning. First, the excited line is represented through an equivalent frequency-domain m-port, and the effects of the lightning excitation are taken into account via terminal equivalent lumped sources. In Frequency domain it is easy to include in the model the skin-effect in the wires and the finite conductivity of the ground. By means of a semi-analytical inversion procedure, the time-domain equivalent circuit is derived. This allows treating in a correct way the study of fast transient and non-linear loads such as surge arresters. Using the above procedure, simulations have been carried out in order to evaluate the shielding effect of the ground wires and to analyse the effects of surge arresters. The results agree with those obtained in literature by using different methods.