Globality levels of grounding systems

IEC Standard 61936-1 “Power installations exceeding 1 kV a.c.” defines the “Global Grounding System” (GGS). It consists essentially in the interconnection of the MV/LV grounding systems, generally at least by means of the MV cables metal sheaths and/or of dedicated ground conductors buried along the MV cable lines. The interconnection of grounding systems involves a significant reduction of the apparent grounding resistance at the MV/LV substations, by creating a metallic ground-fault current path in parallel with the ground which drains away most of the fault current. Due to the mentioned ground resistance reduction, the IEC 61936-1 allows to adopt simplified, relaxed design criteria for the individual grounding systems. The paper suggests recognizing the four “globality” levels of grounding systems in a common zone of influence. It is highlighted the analysis of the interferences between more ground electrodes that can be sensitive for special power systems as data centers and hospitals. It suggests ways to mitigate transferred potentials and a graphical test by a rolling sphere that can be useful to verify the integration of aggregate of ground systems.