0093-9994 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TIA.2018.2875383, IEEE Transactions on Industry Applications Abstract-The interconnection of grounding systems of HV-MV stations via the armors of medium voltage cables, is herein analyzed to verify the effects on touch voltages in ground-fault conditions. The major contributions of this paper are two: the analysis of the impact of a HV ground-fault on a Global Grounding System (GGS), and the analysis of the parameters that may affect safety due to the interconnection between HV- MV stations and the GGS. The authors have analyzed cases when the connection of a HV-MV station to a Global Grounding System improves safety, and when may introduce hazards under ground-fault conditions. Two main issues are herein discussed: 1) the transfer of dangerous voltages to substations, due to ground- faults occurring at the HV-MV station; 2) the reduction in the magnitude of the ground potential rise caused by ground-fault conditions at substations, due to the connection of their ground grids to the HV-MV station’s grounding system. The paper, by examining various grid configurations, demonstrates that in some instances the inclusion of HV-MV stations in the Global Grounding System may reduce the level of protection against touch voltages, and that this depends on the following elements: the number of MV lines fed by the faulted station, the number of MV-LV substations per line, the value of the ground resistance of the substations, and the distance between the substations. The paper has practical relevance for both utilities distribution systems and industrial facilities supplied by the MV power grid. Keywords—Global Grounding System; Ground fault; HV/MV station; Electrical Safety; Interconnected grounding systems. I. INTRODUCTION Substations do require grounding systems, whose crucial task is the protection of persons from the effects of ground- faults [1]-[3]. The efficiency of grounding systems depends on the type and extension of their components, as well as on the distribution of fault currents. Residential areas, city centers, or industrial parks offer the optimal conditions for protective grounding due to their interconnection through cables and metal pipes, and the vicinity of grounding electrodes. Based on these conditions, the term Global Grounding System (GGS) was coined [4]. A GGS is defined as the combination of local grounding M.L. Di Silvestre, L. Dusonchet, S. Favuzza, S. Mangione, L. Mineo, E. Riva Sanseverino, G. Zizzo are with the Department of Energy, Information Engineering and Mathematical Models (DEIM) of the University of Palermo, Palermo, I-90128 Italy M. Mitolo is with the Electrical Department of the Irvine Valley College, Irvine, CA 92618, USA. (e-mail: marialuisa.disilvestre@unipa.it; luigi.dusonchet@unipa.it ; salvatore.favuzza@unipa.it; stefano.mangione@unipa.it; liliana.mineo@unipa.it; mitolo@ieee.org; eleonora.rivasanseverino@unipa.it; gaetano.zizzo@unipa.it) systems, obtained by their interconnection, which ensures, thanks to their proximity, that no dangerous touch voltages can arise [5]. Per [6], within a GGS, the verification of the resistance to ground of the grid, the ground potential rise (GPR), and touch and step voltages in substations, and in Distribution System Operator (DSO) high-voltage stations, is no longer a requirement. The GGS is therefore a concept that may dramatically change the process for evaluating electrical safety in substations. As shown in [7], current literature on GGSs includes studies on single-line-to-ground faults (SLGs), and double ground- faults (2GFs) occurring inside MV-LV substations, while SLGs occurring inside a HV-MV stations connected to a GGS are not considered. The major contributions of this paper are two: the analysis of the impact of an HV ground-fault on a Global Grounding System (GGS), and the analysis of the parameters that may affect safety due to the interconnection between HV-MV stations and the GGS. In particular, the authors have examined the effects of SLGs occurring at the high-voltage side of a HV-MV station that impact substation(s) fed by that station. When such a fault occurs, high currents may circulate [8], which may create large GPR, and cause hazardous touch voltages in neighboring installations. This situation is particularly crucial when HV-MV stations, or HV lines [9], are located in urban areas, close to residential buildings. It is important to note that the overhead ground wire (OGW), or the armors (or shields), of lines and MV cables supplying MV-LV substations, may be connected to the ground grid of the HV-MV station. The authors herein discuss: 1) the transfer of dangerous voltages to substations, due to ground-faults occurring at HV-MV stations; 2) the possible reduction in the magnitude of the GPR at substations, due to the connection to the HV/MV station’s grounding system. As is customary in studies concerning safety problems, the models used for calculating ground-fault currents do not consider initial transient phenomena [10]-[13]. II. METHODOLOGY The effects of the HV/MV station on the GGS are investigated using two equivalent lumped-parameters circuits for simulating the SLG event at the HV-MV station, and at the MV-LV substation. The calculation models are derived from [14] and from On the Interconnections of HV-MV Stations to Global Grounding Systems M.L. Di Silvestre, L. Dusonchet, S. Favuzza, Senior Member, IEEE, S. Mangione, L. Mineo, M. Mitolo, Senior Member, IEEE, E. Riva Sanseverino, G. Zizzo, Senior Member, IEEE