The earthing system of an electricity substation is of the utmost importance, primarily to ensure electrical safety for persons working within or near the substation and also to limit any electrical interference with third-party equipment to acceptable values. Adequate forethought can help prevent unwanted surprises and avoid unnecessary and sometimes retrospective expenditure to achieve an adequate earth grid impedance value. The process starts with accurate soil resistivity measurement and the derivation of an electrical equivalent of the soil structure at the site. This in turn enables the options for achieving an adequately designed grid to be assessed in order to find the most economic solution.
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