Search results for "grounding system"
showing 10 items of 10 documents
Finite difference time domain simulation of soil ionization in grounding systems under lightning surge conditions
2004
This paper proposes a Maxwell’s equations finite difference time domain (FDTD) approach for electromagnetic transients in ground electrodes in order to take into account the non linear effects due to soil ionization. A time variable soil resistivity method is used in order to simulate the soil breakdown, without the formulation of an initial hypothesis about the geometrical shape of the ionized zone around the electrodes. The model has been validated by comparing the computed results with available data found in technical literature referred to concentrated earths. Some application examples referred to complex grounding systems are reported to show the computational capability of the propos…
Effects of double ground faults in Wind Farms collector cables
2015
Medium Voltage collector cables of Wind Farms have metal shields connected to the grounding systems of the towers and of the connection station. Thanks to this bonding, when a ground fault occurs, the fault current splits itself among all the grounding systems of the wind farm, this causing a reduction of the ground potential rise at the fault location. Nevertheless, in presence of double ground faults, very high ground potential rises occur at the two fault locations and safety against electric shock is not always assured. In order to study this issue, the paper presents a model for simulating in a simple way the effects of double ground faults occurring in Medium Voltage collectors of ext…
Efficient modeling of a combined overhead cable line for grounding-system analysis
2008
Simple compact models for combined overhead-cable lines supplying a substation are presented as an extension of a previous paper for grounding system analysis. The overhead line section can be equipped with uniform or combined ground wires, whereas the cable line section can consist of coated metal sheathed cables, with/without intermediate grounding, or uncoated metal sheathed cables in continuous contact with the earth. Besides the calculation of the earth current at the faulted substation, the proposed modeling method allows the evaluation of the leakage current at the transition station, where cables are connected to the overhead line, as well as at critical overhead line towers. In thi…
The Global Grounding System: Definitions and guidelines
2015
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.
Practical tables for the design of the grounding systems in distribution networks in presence of metallic interconnection
2009
The present paper deals with the dependence of the ground current, due to a single-line-to-ground fault in a secondary substation, on the electrical and geometrical parameters of a Medium Voltage distribution network in which a metallic interconnection between the grounding systems is realized. Examining different situations, some easy-to-use tables are provided for a practical approach to the design of the ground electrodes of the secondary substations in these networks. The relevance of the work is due to the lack in the international standards of specific indications on how to consider the presence of the interconnection elements in distribution networks.
Influence of LV neutral grounding on global earthing systems
2015
International Standards define a Global Earthing System as an earthing net created interconnecting local Earthing Systems (generally through the shield of MV cables and/or bare buried conductors). In Italy, the regulatory authority for electricity and gas requires distributors to guarantee the electrical continuity of LV neutral conductor. This requirement has led to the standard practice of realizing “reinforcement groundings” along the LV neutral conductor path and at users’ delivery cabinet. Moreover, in urban high-load scenarios (prime candidates to be part of a Global Earthing System), it is common that LV distribution scheme creates, through neutral conductors, an effective connection…
A practical method to test the safety of HV/MV substation Grounding Systems
2015
The adequacy of a Grounding System (GS) to the safety conditions has to be periodically tested by measurements. The test methods and techniques used to verify the electrical characteristics of the GS include the measurements of step and touch voltages. The goal of the test is to verify that touch voltage and step voltage remain below a safe value in all the zones of the installation. The measurements can present some operational difficulties. The purpose of this paper is to present the procedure, step-by-step, of a practical method of measuring touch/step voltages in grounding systems located in urban or industrial areas with reduced accessibility. The suggested method uses auxiliary curren…
On the effects of HV/MV stations on global grounding systems
2016
The METERGLOB project has faced the issue of the identification of Global Grounding Systems. One of the main point of the problem is to define if an interconnection of single grounding systems gives place to a Global Grounding System in any condition and for every kind of ground fault. This paper focuses the attention on what happens in the case of single line to ground fault inside a HV/MV station whose ground electrode is connected to the cable' shields of the MV lines outgoing the station and supplying the secondary substations of a given area.
On the Interconnections of HV–MV Stations to Global Grounding Systems
2019
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 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. The authors have analyzed cases when the connection of an HV-MV station to a GGS improves safety, and then may introduce hazards under ground-fault conditions. Two main issues are herein discussed: 1) the transfer of dangerous voltages to substations, due to …
Interconnections criteria of grounding grids in global grounding systems
2018
A Global Grounding System is defined as the combination of local grounding systems, obtained by their interconnection, which ensures, thanks to their proximity, that no dangerous touch voltages can arise. The interconnection of grounding systems via the armors of the MV cables, between secondary substations and HV/MV stations is herein analyzed to verify the effects on touch voltages in ground-fault conditions. In particular, two main issues are discussed: 1) the transfer of dangerous voltages to secondary substations, due to ground-faults occurring at the HV/MV station; 2) the reduction in the magnitude of the ground potential rise due to ground-fault conditions at secondary substations, t…