This chapter is devoted to the second objective. Understanding how harmonic voltages propagate in a meshed grid may enable us to estimate objectively where a harmonic filter will be effective. Initially, a sensitivity analysis of multiple filter placements in the part of the Danish 400 kV transmission network under study was performed to assess Energinet’s existing substation selection philosophy in relation to harmonic filter design. Based on the knowledge obtained with the propagation model on voltage propagation in the grid, additional methodologies for objective substation selection are presented. Substations to which the harmonic voltage is preferably propagated are objectively investigated, as is the contribution of each harmonic source to the harmonic distortion level of substations.