Calculation of fault current-division factors and assessment of earth-grid safety at an independent power producer station

This paper calculates fault current-division factors and assesses earth-grid safety at 17.1/161-kV Chiahui independent power producer (IPP). A method based on the grid current is proposed to calculate fault current-division factors and the results are compared with the Endrenyi method as well as the current-distribution electromagnetic-grounding and soil-structure analysis (CDEGS) program. Since the coupling effect of overhead earth wires to phase conductors was not taken into account by the Endrenyi method, the computed fault current-division factor will be greater than those obtained by the proposed method and CDEGS program. Moreover, mesh and step voltages are computed to compare with minimum touch and step voltages for assessing earth-grid safety, respectively. As a result, the design of earthing systems at 17.1/161-kV IPP station is safe for humans with 50 kg and 70 kg body weight.