1 --Global Earthing Systems (GESs), created by the interconnection of local Earthing Systems (ESs), should guarantee the absence of dangerous touch voltages. According to international Standards, one of the reasons for this safety characteristic of GESs is that MV and LV grounding systems form a quasi-equipotential area.Typical examples of GESs are in city centers, thanks to the high number of interconnected grounding systems in the area. For this reason, in addition to ground-grids, also other metallic parts with different primary functions shall be considered: for example, water and gas pipes, tramway tracks and building foundations can modify the electric potential distribution in the area.In this paper, a model based on the Maxwell's sub-areas method (MaSM) is used to evaluate how buried metallic parts, not intentionally connected to ground-grids, modify the electric potential on the soil surface.Firstly, the MaSM model is validated with experimental measurements on a simple electrodes configuration. The measured voltages are compared with the MaSM results and with the results obtained with a FEM model simulated with COMSOL Multiphysics.Then the simulations are carried out on a realistic urban test case.
When a single line to ground fault happens on the MV side of a HV/MV system, only a small portion of the fault current is injected into the ground by the ground-grid of the faulty substation. In fact the fault current is distributed between grounding electrodes and MV cables sheaths. In systems with isolated neutral or with resonant earthing this may be sufficient to provide safety from electric shock. Experimental measurements were performed on a real MV distribution network: a real single line to ground fault was made and fault currents were measured in the faulty substation and in four neighboring substations. In this paper the problem of fault current distribution is introduced, the test system is described and the measurements results are presented.
The present paper presents the preliminary results of the ongoing Italian METERGLOB project on the contribution given by the exposed conductive parts to a Global Grounding System. One of the expected results of METERGLOB is to carry out guidelines for the identification of a Global Grounding System. These guidelines must be defined on the basis of the definitions and methods present in the current international standards on grounding and safety. In the paper some definitions and elements to be taken into account for the identification of a Global Grounding System are given
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