Search results for "Grounding"
showing 10 items of 41 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…
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…
The Quest for Global Safety
2007
The authors present a systematic study on the factors that have influence on the establishment of the safety conditions ensuring the rise of Global Earthing Systems. Starting from the definition of Global Earthing System given by CENELEC Document HD 637 SI and from the results of the studies done on the last years on the interconnected earthing systems inside MV networks, the paper proposes some directions of deepening on the topic of Global Safety. Some of the themes whom the paper deals with are: the correct definition of proximity, interconnection and quasi-equipotentiality of the earth electrodes belonging to a Global Earthing System; the influence of the presence of HV/MV stations on h…
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…
Analysis of ground fault current distribution along nonuniform multi-section lines
2008
In case of a substation supplied by a combined overhead-cable line, most of the ground fault current flows through the cable sheaths and discharges into the soil surrounding the point of discontinuity, where cables are connected to the overhead line. In the paper a new method is presented for computing the ground fault current distribution in case of feeding line consisting of two or more different sections, i.e. part overhead and part underground cable. Besides the calculation of the earth current at the fault location, the leakage current at the transit/transition stations as well as at the overhead line towers can be evaluated, in order to ensure proper safety conditions. Based on the tw…
Towards Dialogic Teaching in Science: Challenging Classroom Realities through Teacher Education.
2013
Lehesvuori, Sami Towards Dialogic Teaching in Science: Challenging Classroom Realities through Teacher Education Jyvaskyla: University of Jyvaskyla, 2013, 87 p. (Jyvaskyla Studies in Education, Psychology and Social Research ISSN 0075-4625; 465) ISBN 978-951-39-5151-1 (nid.) ISBN 978-951-39-5152-8 (PDF) Diss. Finnish summary The aim of this study was to explore dialogic teaching in school classroom and teacher education contexts. Despite moves towards more socially-oriented and student-centred curricula, science classroom communication remains prevailingly authoritative and monologic. In order to address the dialogic gap existing in the field, within this study an intervention was developed…
Student participation in peer interaction
2021
This study explores how students deal with material resources in their peer interaction when working in pairs in an open-ended problem-solving task. The productive use of material resources can be expected to support successful peer work. However, research into social phenomena in peer interaction is needed in order to identify and describe productive and less productive forms of dealing with material resources as students participate in open-ended problem-solving tasks. Consequently, this explorative study responds to this research need. Based on multimodal data, including video recordings, transcribed talk and the written contributions from four pairs of Year 7 students aged 12-13 years, …
Simple Circuit Models for Studying Global Earthing Systems
2007
The paper proposes three simple circuit models for the simulation of the behaviour of a global earthing system during different fault events. The models allow one the evaluation of the maximum earth potential rise at every possible fault location and for every possible fault event. The three considered fault events are: single-line-to-earth fault inside a MV/LV substation, double-earth-fault in a MV line, single-line-to-earth fault inside a HV/MV station. After having illustrated the hypotheses at the basis of the study, the circuit models for the three fault events are presented and a numerical example shows how to use them in order to check the "global safety" of the interconnected earthi…
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…
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…