Tests and monitoring of grounding systems in HV/MV substations

Each grounding system (GS) needs periodical measurements to control its adequacy to the safety conditions. The tests of step and touch voltages are the sole measurements available in urban or industrial areas with reduced accessibility. In fact, in these areas, the classic measurements used to verify the electrical characteristics of the GS present generally some operational difficulties. The auxiliary current electrodes can be located at short distances and this operational way the test methods and techniques present conservative values in comparison to the prospected true values measurable adopting a remote auxiliary electrode. The location of auxiliary current electrodes at short distance make easier to keep them permanently installed and so permit the monitoring of the adequacy of grounding systems. This paper presents the measuring touch/step voltages procedure that provides conservative results showing some case studies done in grounding systems of HV!MV substations. It is essential to have the map of the constitution and configuration of the GS, to know its data and the location of the various equipment and buildings, to know the presence of extraneous conductive parts inside and in proximity of the substation, such as other GSs. The field measurements require a good experience of the operator that can be learned by carrying out measurements in cases of GSs with influence zone accessible so that it is possible to compare the traditional method with a remote electrode and the method at short distance.