Assessment of Earthing System Effectiveness at 33kV Substations in Bauchi State

This study assesses the effectiveness of earthing systems at four 33kV transmission substations in Bauchi State, North East Nigeria. Adequate earthing is a fundamental safety and operational requirement in electrical substations, ensuring that fault currents are safely dissipated into the earth, touch and step voltages remain within permissible limits during fault conditions, and equipment insulation is protected from transient overvoltages. Soil resistivity measurements were conducted at each substation site using the Wenner four-pin method at multiple electrode spacings to characterise the soil profile. Earth grid resistance was measured using the fall-of-potential method with a calibrated digital earth tester. Touch voltage and step voltage calculations were performed in accordance with IEEE 80 and the relevant sections of IEC 61936 using the measured soil resistivity and earth grid dimensions. Results reveal that two of the four substations exhibit earth grid resistance exceeding the 1-ohm target recommended for substations of this voltage class. Calculated touch voltages at these substations exceed the safe threshold prescribed by IEC 61936 under the maximum fault current conditions recorded at the substations. Soil resistivity at the affected sites is higher than assumed in the original substation design due to the predominantly rocky laterite composition of the terrain. Corrective measures recommended include installation of additional horizontal earth conductors, use of earthing compound to reduce contact resistance, and ground enhancement material injection around electrode rods. Keywords: earthing system, substation safety, soil resistivity, touch voltage, Bauchi State.