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Examination of the effectiveness of the grounding systems of distribution substations

Grounding system is a major factor for the electrical safety of distribution substations, in an effort to maintain a low impedance path to earth for fault currents for the protection of the electrical system against internal and external faults and to ensure that the ground potential rise will not exceed the limits set for touch and step voltages. Thus, the achievement of low ground resistance values is critical in order to limit the arising touch and step voltages, according to national and international standards. The geometry of the grounding system, the soil resistivity, the duration of the fault current and the addition of a surface layer are crucial factors determining the efficacy of a grounding system. In the present work, several grounding systems configurations of distribution substations are studied. For each system, both the achieved ground resistance value and the developed touch and step voltages are computed by using an appropriate software tool.