Enhancement of the Grounding System of 132/33 kV Sub-transmission Station via an ETAP-Based Approach

Abstract

Using the IEEE approach for grounding design and ETAP software for system modelling, this study seeks to enhance the grounding system at the 132/33kV Afam 1 Sub-transmission station. To get the desired effects, the touch voltage, step voltage, and mesh voltage are chosen. The findings indicate that the current grounding system of the station is in terrible shape. Three of the six grounding pits of the station have been undermined, two have been vandalised, and the one pit that is still in place is insufficient to support the station. Based on the results of the violations, the earth resistance values for Pits 1, 2, and 3 are 2.63, 1.25, and 1.16, respectively. The study used 1.5 bags of salt, six bags of ashes and some water to reduce soil resistance in pits 1, 2, and 3. Soil resistance in pits 1, 2, and 3 was reduced to 0.67, 0.59, and 0.5, respectively, after treatment, resulting in a 70% reduction in resistivity. Pits 4 and 5 require the installation of new grounding systems in place of existing ones. The grid structure of the sub-transmission station comprises squares that are 100 m by 90 m in size, making a total mesh area of 9000 m. The X-axis has 18 conductors, and the Y-axis has 19 conductors. The grid conductor was buried at depth of 0.6 metres, its diameter is 16 millimetres, its total length is 5972 metres, the crushed rock thickness is 1 metre, there are 280 ground rods, and each earth rod is 3 metres long. The station's ground rod spacing is 8 metres. The investigation also discovered that for a 70-kilogramme person with a 0.5-second fault length and a 0.6 current division factor, a fault current of 13785A and a touch voltage of 557.3 Volts were calculated. The temperature at which the thermal coefficient of resistance is zero degrees Celsius, the ambient temperature and the maximum temperature are all fixed at 40 degrees Celsius. The allowable touch voltage and the permitted step voltage at the fault location must be 529.29 and 450.87 volts, respectively, based on the 3-kA ground short-circuit current and the 15 ratio. The ground potential rise (GPR) was 2098.7 Volts, the permitted step voltage was 2823.6 Volts, and the actual step voltage was 205.4 Volts. The grid works safely because the GPR is within allowable bounds. From the findings, treating the soil resistivity in pits 1, 2, and 3 and replacing the grounding systems in pits 4 and 5 outrightly are the best ways to stop electrical failures and fatalities. The study recommends that the station earth resistance be checked annually using an earth resistance tester.