In this paper, the authors present an electromagnetic model suitable to investigate transient performance of electric power substations grounding systems, working in a distributed programming environment. The numerical model, represented by a modified version of the electric field integral equation in frequency domain, is solved by means of the method of moments according to the direct and the iterative numerical formulations. The two computational schemes are described and solved by means or parallel solutions differently grained and oriented to distributed memory computers. Test results, which illustrate the capability of the proposed schemes, are reported and the performances are assessed by using the 128-node Cray T3D architecture.