Search results for "grounding"
showing 10 items of 41 documents
Fall of Potential Measurement of the Earth Resistance in Urban Environments: Accuracy Evaluation
2019
Both Standards EN 50522 and IEEE 81 propose the fall of potential method (FPM) to carry out the measurement of the resistance to earth ( $R_{\text{ES}}$ ) 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. Furthermore, unknown buried metallic parts and interconnections among ESs could modify the earth potential profile of the area, affecting the measurement results. In this paper, the key-issues that influence the measured $R_{\text{ES}}$ when the FPM is used in an urban environment are presented. A parametric analysis, carried out with Comsol Multiphysic…
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…
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…
Student-initiated multi-unit questions in EMI classrooms
2021
This conversation analytic study investigates student-initiated multi-unit questions (MUQs) in whole class interaction. Based on a corpus of 30 hours of videotaped interactions from teacher education classrooms in an English-medium instruction university, we demonstrate that students use MUQs to introduce topics, either by recontextualizing some aspect of the prior topic, or alternatively, without these cohesive ties, which requires more interactional work to achieve intersubjectivity. Findings reveal that MUQs render student professional concerns more relevant and salient, foregrounding those inquiries as a space for launching topics. Students bring up issues such as ways of handling parti…
Manipulation of teenagers through advertising: a critical discourse approach
2011
[EN] The possible harmful effects of advertising in magazines aimed at teenagers have not lost relevance.Thus the aim of this article is to explore the linguistic characteristics used as foregrounding devices in a corpus of English advertisements aimed at teenagers. My underlying premise is that some linguistic messages or images convey information which is picked up by teenagers creating in them the desire to obtain certain products. In my analysis I attempt to ascertain, if any, what kind of linguistic control and what linguistic devices advertisers use to achieve their goal. Additionally, I try to find out to what extent the power of advertising has something to do with social problems r…
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…
Building and Maintaining the Common Ground in Web-Based Interaction
2002
In this paper, the main purpose is to explore how participants establish and maintain the common ground in the computer-based conferences. Previous studies assume that before the participants can reach the deeper level interaction and learning, they have to gain an adequate level of common ground (Dillenbourg, 1999; Baker et al., 1999; Veerman, 2000). Subjects were 68 pre-service teachers and 7 mentors from three universities who participated in the web-based conferencing course for eight weeks. The results assume that in deeper level discussions it is essential that participants, especially fellow students did give not only the evidence about their own understanding by using written feedba…
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…
Android tool to evaluate grounding resistance
2015
In the absence of sources of rapidly varying field, the study of the potential distribution determined, in a linear medium, by a geometrically complex grounding may be conducted by applying the method of superposition of the effects, known as method of subareas of Maxwell. Such approach can be usefully employed in an educational tool intended for students of electrical engineering.
Ground Fault Current Distribution in Substations Supplied by Nonuniform Multi-Section Lines
2007
he paper presents a general method for computing the distribution of substation ground fault current. The feeding line can be entirely homogeneous along its whole length or consisting of two or more different sections, i.e. part overhead and part underground cable. Based on the two-port theory, the proposed method allows to take into account all the relevant conductively and inductively coupled parameters which take part to the distribution of the fault current and can be easily implemented in a computer program. Numerical examples demonstrate the high efficiency of the proposed method.