Search results for " grounding"
showing 10 items of 27 documents
Currents Distribution During a Fault in an MV Network: Methods and Measurements
2016
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 tes…
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…
On multi-objective optimal reconfiguration of MV networks in presence of different grounding
2015
The present work faces the traditional multi-objective optimal reconfiguration problem of a distribution grid including the safety issue in the objective functions. Actually, in many medium voltage networks still transformers with ungrounded neutral and with resonant grounded neutral coexist in the same area. This may be sometimes cause of problems during a single-line-to-ground fault if the ground electrodes of one or more cabins, initially designed for satisfying the safety conditions in a resonant grounded neutral network, after the reconfiguration are in a grounded neutral one or vice versa. In the paper a safety objective function is defined and the Non dominated Sorting Genetic Algori…
Grounding ontologies in the external world
2017
The paper discusses a case study of grounding an ontology in the external world by a cognitive architecture for robot vision developed at the RoboticsLab of the University of Palermo. The architecture aims at representing symbolic knowledge extracted from visual data related to static and dynamic scenarios. The central assumption is the principled integration of a robot vision system with a symbolic system underlying the knowledge representation of the scene. Such an integration is based on a conceptual level of representation intermediate between the sub-symbolic processing of visual data and the declarative style employed in the ontological representation.
Finite-Difference Time-Domain Simulation of Tower and Grounding Subjected to Lightning
2015
In this paper the behavior of a tower and its grounding system, subjected to a lightning, is faced. Finite difference time domain (FDTD) method has been chosen in order to study the non-linear time domain behavior of the system. The electromagnetic problem has been described by using two type of first order time derivative equations: Maxwell's equations and Telegraph equations. Aim of this work is to evaluate the possibility of a flashover between tower and power line, by considering different cases of study.
Current and Voltage Behaviour During a Fault in a HV/MV System: Methods and Measurements
2015
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 te…
Distribution of Ground Fault Current in Substations Fed by a Combined Overhead-Cable Line
2005
When a substation is fed by a combined overhead-cable transmission line, in case of a fault to ground within the substation a consistent part of the fault current flows through the cable sheaths toward the remote source and discharges into the earth at the transition station, where cables are connected to the overhead line. This phenomenon, named "fault application transfer", may result in high ground potentials at the transition station which may cause shocks and equipment damage. In this paper a simple but accurate method on modelling a combined overhead-cable line is presented, allowing the computation of the fault current transferred at the transition station. Numerical analysis shows t…
On the distribution of lightning current among interconnected grounding systems in medium voltage grids
2018
This paper presents the results of a first investigation on the effects of lightning stroke on medium voltage installations' grounding systems, interconnected with the metal shields of the Medium Voltage (MV) distribution grid cables or with bare buried copper ropes. The study enables us to evaluate the distribution of the lightning current among interconnected ground electrodes in order to estimate if the interconnection, usually created to reduce ground potential rise during a single-line-to-ground fault, can give place to dangerous situations far from the installation hit by the lightning stroke. Four different case studies of direct lightning stroke are presented and discussed: (1) two …
A study on the use of bare buried conductors in an extended interconnection of earthing systems inside a MV network
2005
In the field of electrical safety an important topic is the transmission of voltages, during an earth fault, inside an extended interconnection of local earthing systems. The paper presents a study, with reference to the MV networks, about those systems where the interconnection between the earth electrodes of the electrical installations is carried out using bare buried conductors. Starting from the description of the circuital model of a bare buried conductor interconnecting together the earth electrodes of two MV/lv substations, the mathematical model of the whole interconnected earthing system is found. Finally, the results of some simulations, giving the distribution of the fault curre…
Earth resistance measurements in urban contexts: Problems and possible solutions
2017
Both EN 50522 and IEEE Std. 81 propose the Fall of Potential Method (FPM) to carry out the measurement of the resistance to earth of an Earthing System (ES). However, in urban areas, the recommended distances between the ES and auxiliary electrodes are not easy to respect, due to the presence of buildings and tarmac. Moreover, unknown buried metallic parts, as well as the interconnection among the ESs made by the Distributor System Operator, could modify the earth potential profile of the area, affecting the measurement results. In this paper, the issues that could affect the measurement result if FPM is used in an urban context are presented. A parametric analysis, carried out with Comsol …