This paper proposes a methodology for interfacing the frequency-domain harmonic electromagnetic models of complex grounding systems (buried in horizontally stratified multilayer medium) with the EMTP-ATP software package, for the purpose of transient analysis of electrical power systems. It comprises three individual steps: (1) construction of the frequency-dependent nodal admittance matrix for the arbitrarily positioned system of conductors in horizontally stratified multilayer medium, (2) application of the vector fitting technique to this frequency-dependent nodal admittance matrix and (3) construction of the Foster-type networks from the results of the vector fitting and their interfacing with the EMTP-ATP environment. The proposed methodology is general and could be applied to different kinds of grounding systems, ranging from wind turbine grounding systems, to groundings of high voltage transmission line towers and towers carrying GSM base stations. (C) 2014 Elsevier Ltd. All rights reserved.