Impact of MV Ground Fault Current Distribution on Global Earthing Systems

Global earthing systems (GESs), created by the interconnection of local earthing systems, should guarantee the absence of dangerous touch voltages. One of the reasons for this safety characteristic of GESs is the fault current distribution between grounding electrodes and medium-voltage (MV) cable sheaths: Only a small portion of the fault current is injected into the ground by the ground grid of the faulty substation. In systems with isolated neutral or with resonant earthing, this effect may be sufficient to provide safety from electric shock. In this paper, a model describing the behavior of the MV distribution system with interconnected grounding electrodes during a ground fault is built. It is then used to analyze the impact of different factors on the fault current distribution. A sensitivity analysis is performed, varying the main parameters, and the results are used to draw some conclusions on the current distribution influence on GESs.