Influence of LV Neutral Grounding on Global Earthing Systems

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, trough neutral conductors, an effective connection between grounding systems of MV/LV substations, modifying Global Earthing System consistency. Aim of this paper is to evaluate the effect, in terms of electrical safety, of the above mentioned LV neutral distribution scheme when an MV-side fault to ground occurs. At this purpose simulations are carried out on a realistic urban test case and suitable evaluation indexes are proposed

A Practical Method to Test the Safety of HV/MV Substation Grounding System

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 current electrodes located at short distances. This paper demonstrates by test measurements done in a real case that the method provides conservative results

Allylic amination of unactivated olefins by nitroarenes, catalyzed by ruthenium complexes. A reaction involving an intermolecular C-H functionalization

A reaction is reported, resulting in the allylic amination of an unactivated olefin, cyclohexene, by a nitroarene, catalyzed by Ru-3(CO)(12)/Ar-BIAN (Ar-BIAN = bis(arylimino)acenaphthene), under CO pressure. The reaction involves an intermolecular catalytic C-H functionalization by a transition metal complex. Best results (selectivity up to 81.9%, with a substrate/Ru-3(CO)(12) ratio = 50) are obtained by using nitroarenes bearing electron-withdrawing substituents and Ph-BIAN as a ligand. Other olefins can also be employed in place of cyclohexene. The reaction mechanism has been investigated. The reaction is first order in nitroarene and olefin, which is used as solvent in most cases, but the rate equation also contains an olefin-independent term. A rate acceleration by small amounts of toluene in the solvent mixture is due to a faster formation of Ru(CO)(3)(Ar-BIAN) from Ru-3(CO)(12) and Ar-BIAN in its presence. This last complex is in equilibrium with the active species Ru(Ar-BIAN)(CO)(2)(cyclohexene), and its direct reaction with the nitroarene accounts for the olefin-independent term in the rate law. The reaction of Ru(CO)(3)(Ar-BIAN) with nitroarenes gives Ru(CO)(2)(Ar-BIAN)(eta(2)-ArNO), which has been isolated in one case, but this complex is not an intermediate in the synthesis of allylamines. Coupling between a coordinated nitrosoarene and a coordinated olefin appears to be responsible for the C-N bond formation

Tests and monitoring of grounding systems in HV/MV substations

Each grounding system (GS) needs periodical measurements to control its adequacy to the safety conditions. The tests of step and touch voltages are the sole measurements available in urban or industrial areas with reduced accessibility. In fact, in these areas, the classic measurements used to verify the electrical characteristics of the GS present generally some operational difficulties. The auxiliary current electrodes can be located at short distances and this operational way the test methods and techniques present conservative values in comparison to the prospected true values measurable adopting a remote auxiliary electrode. The location of auxiliary current electrodes at short distance make easier to keep them permanently installed and so permit the monitoring of the adequacy of grounding systems. This paper presents the measuring touch/step voltages procedure that provides conservative results showing some case studies done in grounding systems of HV!MV substations. It is essential to have the map of the constitution and configuration of the GS, to know its data and the location of the various equipment and buildings, to know the presence of extraneous conductive parts inside and in proximity of the substation, such as other GSs. The field measurements require a good experience of the operator that can be learned by carrying out measurements in cases of GSs with influence zone accessible so that it is possible to compare the traditional method with a remote electrode and the method at short distance

Currents distribution during a fault in a MV Network: Methods and measurements

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

Current and voltage behaviour during a fault in a HV/MV system: Methods and measurements

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 neighbouring substations. In this paper the problem of fault current distribution is introduced, the test system is described and the measurements results are presented

Influence of LV neutral grounding on global earthing systems

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 between grounding systems of MV/LV substations, modifying Global Earthing System consistency. Aim of this paper is to evaluate the effect, in terms of electrical safety, of the above mentioned LV neutral distribution scheme when an MV-side fault to ground occurs. At this purpose simulations are carried out on a realistic urban test case and suitable evaluation indexes are proposed

A practical method to test the safety of HV/MV substation Grounding Systems

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 current electrodes located at short distances. This paper demonstrates by test measurements done in a real case that the method provides conservative results

The Global Grounding System: Definitions and guidelines

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