Evaluation of Voltage Exposures Due to AC/DC Stray Currents

Stray currents leaking from DC and AC electrical installations may flow through buried metal works towards their sources. Such currents may circulate through intentional electrodes, for example dwelling units and railways grounding systems, but also through building and tunnels metal frames, as well as, water and gas utility pipelines. Besides the corrosion phenomena, triggered over the aforementioned metal parts by DC currents, the stray currents may energize these conductive parts, exposing persons to touch voltages. This paper proposes an approach to evaluate the voltage exposure appearing on the aforesaid metal parts, based on the estimation of an appropriate ground-resistance matrix. This matrix, used in conjunction with a system of circuit equations, will yield voltage and current associated to the interfering electrodes. In the case of standard electrode configurations (e.g. spherical, cylindrical, etc.) the evaluation of the above mentioned matrix may be analytically carried out. To take into account complex electrode geometries and/or non-homogeneous soil conditions, numerical elaboration based on the method of the moments will be employed. Historical cases are presented and discussed.