A Feasibility Study on the Use of Concrete Pole Bases as a Grounding Topology for Distribution Systems Hugo A. D. Almaguer, Rafael A. Coelho FURB – Regional University of Blumenau Blumenau, Brazil hugo@furb.br, vgt.rac@gmail.com Plínio Luiz Nosaki RGE - Rio Grande Energia Caxias do Sul, Brazil Vilson Luiz Coelho, Alexandre Piantini University of São Paulo Institute of Energy and Environment São Paulo, Brazil vilson.coelho@vlc.eng.br, piantini@iee.usp.br Abstract—This paper presents an analysis of the behavior of concrete pole bases under lightning impulse currents and their application as a grounding topology for overhead power distribution lines. For this purpose, the Transmission-Line Modeling Method (TLM) has been used to simulate the transient grounding impedance curve. An analytical expression has been developed to compute the ground resistance and a good agreement has been obtained between the models. Comparisons are presented with results corresponding to a single vertical rod. The use of concrete pole bases as grounding structures is shown to be a viable and economical alternative to be applied in some power distribution grounding systems in substitution to single rods. Keywords-concrete pole; grounding modeling; overhead power distribution lines; Transmission-Line Modeling Method. I. INTRODUCTION Lightning is one of the main sources of power system disturbances, causing overvoltages and having an important effect on the quality of the power supplied [1]-[12]. Therefore, grounding aspects must always receive special attention. Grounding systems of overhead power distribution lines are characterized by small dimensions due to the cost and constraints imposed by the locations of construction. The most commonly adopted topology has a few number of aligned and interconnected conductor rods. Usually only one or three rods are set, whereas in some special critical soil conditions up to seven rods may be used. On the other hand, the concrete pole is the most common type currently used in overhead power distribution networks. This kind of structure has an internal metal reinforcement and its base penetrates the soil to a depth of up to a few meters, as shown in Fig. 1. In this context, the aim of this paper is to present a feasibility study of the use of concrete pole bases as a grounding topology for overhead power distribution lines. For this purpose two models, one analytical and another numerical, are presented for the calculation of the ground resistance of the concrete pole base. The results are compared with those obtained from known analytic expressions for the typical grounding systems previously mentioned. Figure 1. Representation of a typical concrete pole base. The numerical simulations were performed using the Transmission-Line Modeling Method (TLM). Besides the calculation of the ground resistance, this method also allows the analysis of the transient behavior of the ground impedance and the distribution of electric potentials in the structure when it is hit by lightning. II. PROPOSED MODELS FOR THE CONCRETE POLE BASE A. Numerical TLM Model The TLM is a time-domain differential equation method based on the equivalence between the transmission lines theory and the electromagnetic field equations. In this work, the TLM - 3D mesh employed is based on the Symmetrical Condensed Node (SCN) [13]. A set of cubic cells represent the spatial region under interest, as shown in Fig. 2. This work has been supported by the CPFL and RGE power utilities in the Brazilian Electricity Regulatory Agency (ANEEL) R&D Program.