Contribution to Tagg´s methodology in the resistance measurement of earth-electrode systems at reduced distances

The main challenge of this article is to show a feasible solution for measuring earth resistance at short distances, considering that in practical terms, such is the condition found in the great majority of urban substations. A field test with 4 grounding meshes with different geometric configurations was implemented and used in order to perform a great number of measurement tests. Based on all the data and the processing of the measurement results, a mathematical model called the Extended Tagg Method was developed in order to establish the correct distance to carry out the measurement of earth resistance at short distances. A discussion on the proposed method, as well as its analysis of accuracy and susceptibility in view of external interference is performed, as well as its validation in real substations.