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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

A General Inception Criteria For The Positive Upward Leaders In Cloud-to-Ground Lightning

Prasanth Kumar, B 07 1900 (has links) (PDF)
No description available.
72

Lightning protection of wind turbines

Peesapati, Vidyadhar January 2010 (has links)
Wind turbines are the largest contributor to renewable energy both in Britain and the rest of Europe. With a rise in the installed capacity and an increase in offshore wind energy due to governments green targets by 2020, there has been a large development in new wind turbines for optimized performance. The present thesis deals with the uncertainties in regards to the lightning phenomenon on wind turbines with emphasis on the rotor blades. Rotor blades are the most expensive part to replace in the event of lightning related damage. The research presents results based on lightning data analysis on wind turbines, backed up by finite element analysis testing of wind turbine systems. The final chapters include the testing and improving of lightning protection systems installed on modern day rotor blades. The first part of the thesis deals with the theoretical understanding of the lightning phenomenon and its effect on wind turbine systems. The core work of the research begins with the analysis of lightning data collected over Nysted wind farm and different wind turbines installed over the world. The data analysis helps in identifying the parts of the wind turbine that are at high risk to lightning attachment and related damage. The peak current levels of the lightning strikes seen on the wind turbine are compared with those in modern day lightning standards, and show that historic data in the standards are not an exact match to the real case scenarios. The lightning data analysis also sheds light into the importance of upward initiated lightning, which will become important for large wind turbines, especially in their new offshore environment. A full scale 3D FEA model of a wind turbine, with lightning protection systems installed in its rotor blades, is subjected to electrical stresses to find likely attachment points in regards to upward initiated lightning, and these results are later compared to those found in the data analysis. The second half of the thesis deals with the testing of new materials and prototype blades, to be introduced to reduce their radar cross section. The new materials include a large amount of carbon content which affects the efficiency of the lightning protection system. High voltage and high current tests backed up with finite element analysis have been performed to find how these new materials affect the performance of the lightning protection system. The results indicate that further work needs to be done before these new materials can be integrated into the blade, as they increase the risk of lightning related damage to the blade.
73

Geological Effects on Lightning Strike Distributions

Berdahl, J. Scott 16 May 2016 (has links)
Recent advances in lightning detection networks allow for detailed mapping of lightning flash locations. Longstanding rumors of geological influence on cloud-to-ground (CG) lightning distribution and recent commercial claims based on such influence can now be tested empirically. If present, such influence could represent a new, cheap and efficient geophysical tool with applications in mineral, hydrothermal and oil exploration, regional geological mapping, and infrastructure planning. This project applies statistical analysis to lightning data collected by the United States National Lightning Detection Network from 2006 through 2015 in order to assess whether the huge range in electrical conductivities of geological materials plays a role in the spatial distribution of CG lightning. CG flash densities are mapped for twelve areas in the contiguous United States and compared to elevation and geology, as well as to the locations of faults, railroads and tall towers including wind turbines. Overall spatial randomness is assessed, along with spatial correlation of attributes. Negative and positive polarity lightning are considered separately and together. Topography and tower locations show a strong influence on CG distribution patterns. Geology, faults and railroads do not. This suggests that ground conductivity is not an important factor in determining lightning strike location on scales larger than current flash location accuracies, which are generally several hundred meters. Once a lightning channel is established, however, ground properties at the contact point may play a role in determining properties of the subsequent stroke.
74

An Investigation into the Impacts of Land-Use/Land-Cover on Cloud-To-Ground Lightning Activity

Owen, Nathan Oneal 17 May 2014 (has links)
Cloud-to-Ground (CG) lightning activity was analyzed across the lower Mississippi River valley. The goal was to determine whether certain land use/ land cover (LULC) types supported convective thunderstorms’ generation of CG lightning more than other LULC types. Results indicate that forested regions receive more CG lightning than any other LULC type represented in the study area. However, results also indicate that CG lightning activity can be enhanced locally by very large and/or sprawling areas of urban LULC. When cities from previous research, including Atlanta, GA, and Birmingham, AL, are combined in the rankings with cities in this study, the urban size difference between Little Rock, Arkansas, and Birmingham, Alabama, appears to highlight the area of urban LULC needed to enhance convection. Future research should focus on more cities within this gap of urban LULC area in order to identify the minimum areal expanse needed to alter convective ability over cities.
75

Estimation of the lightning attractive width of high voltage transmission lines

Disyadej, Thongchai 01 May 2010 (has links)
This research is devoted to an investigation on the attractive width of high voltage transmission lines to lightning strikes. In order to design the optimal lightning protection, the estimated number of lightning flashes on the line, which is based on its attractive width, needs to be determined. The investigation was performed using experiments with model tests at the Mississippi State University High Voltage Laboratory. For laboratory experiments, a total of 2,100 negative and positive switching impulse voltages were applied to transmission line models from a conducting rod, which represented a lightning downward leader. Different tested models of transmission lines on a scale of 1:100 were used. The effects of overhead ground wires, phase conductors, tower structures, and the magnitude and polarity of lightning strokes were also studied. The attractive width increased gradually with the height of overhead ground wires and towers as well as the magnitude of the lightning stroke current. Impulse polarity had an impact on the attractive width, and the attractive width for negative polarity was larger than that for positive polarity. The taller tower had more effect on flash distribution to transmission lines than the shorter one. The experimental results agree with the actual transmission line observations published in literature. The new expressions for the attractive width of transmission lines, based on the experimental results, were established. The accurate estimation of the attractive width can help electric power utilities plan transmission systems reliably and economically. The detailed description of the background problem, proposed method, experimental results, and analysis are presented in this dissertation.
76

Inference of charge transfer from lightning flashes in South Africa

Tasman, Jesse Dean, Tasman, Jesse Dean January 2019 (has links)
A dissertation submitted in fulfillment of the requirements to the Faculty of Science, University of the Witwatersrand, Johannesburg, for the degree of Master of Science in the School of Electrical and Information Engineering, June 2019 / The objective of this study is to determine the quantity of charge transferred, in Coulombs, during the continuing current phase of natural cloud-to-ground (CG) lightning flashes over an area in Johannesburg, South Africa. Continuing current is responsible for most thermal related lightning damages such as destruction of property, electrical fires and physical human trauma. The mitigation of lightningrelated risks can be better managed through improved measurement methods of naturally occurring lightning. The application of a point-charge model used to infer charge transfer from changing electric field measurements is detailed. A flatplate antenna with an integrator is set up to record the changing electric fields from lightning flashes. These measurements, along with high-speed video footage to determine continuing current durations, are processed and charge transfer quantities are inferred. From 34 negative lightning strokes with long continuing current (i.e. > 40 ms), the quantity of charge transfer ranges from 0.3 C to 145.5 C and has a mean quantity of 18.3 C. For the 5 recorded positive strokes, the quantity of charge transfer ranges from 3.7 C to 66.6 C / NG (2020)
77

On the Attachment of Lightning Flashes to Grounded Structures

Becerra, Marley January 2008 (has links)
This thesis deals with the physical modeling of the initiation and propagation of upward positive leader discharges from grounded structures during lightning strikes. It includes the analysis of upward leaders initiated under the influence of the electric field produced by a dominant negative cloud charge and due to the combined action of a negative thundercloud and a descending downward stepped negative leader. Thus, a self-consistent model based on the physics of leader discharges is developed for the evaluation of the attachment of lightning flashes to any kind of grounded structure. The predictions of the model have been found to be in good agreement with the results of laboratory long air gap experiments and with classical and altitude rocket triggered lightning experiments. Due to the high application level and predictive power of the developed model, several contributions to the physical understanding of factors influencing the initiation and propagation of upward positive leaders during thunderstorms have been made. For instance, it has been found that the initiation of upward connecting leaders is strongly affected by the average velocity of the downward stepped leader. Similarly, it is shown that the switching voltage impulses used in the laboratory do not “fairly approximate” the electric fields produced by a descending downward leader, as claimed by supporters of Early Streamer Emission (ESE) devices. Furthermore, it is found that the space charge layer created by corona at ground level significantly increases the thundercloud electric fields required to initiate upward lightning leaders from tall objects. On the other hand, it is also shown that the upward leader velocity depends on the downward leader average velocity, the prospective return stroke current, the lateral distance of the downward leader channel and the ambient electric field. By implementing the model to the analysis of complex structures, it has been observed that the corners of actual buildings struck by lightning coincide rather well with the places characterized by low leader inception electric fields. Besides, it has been found that the leader inception zones of the corners of complex structures do not define symmetrical and circular regions as it is generally assumed.
78

Καταγραφή συμβάντων από κεραυνούς στον Ελλαδικό χώρο για την περίοδο 2011-2014

Σταμάτης, Αθανάσιος 27 April 2015 (has links)
Στην παρούσα διπλωματική εργασία παρουσιάζεται η στατιστική ανάλυση των πληγμάτων των κεραυνών στην Ελλάδα κατά τα τελευταία τέσσερα χρόνια (2011-2014). Στο πρώτο κεφάλαιο παρουσιάζεται το φαινόμενο του κεραυνού, τα είδη των κεραυνών και τα φυσικά χαρακτηριστικά του, ενώ στο δεύτερο κεφάλαιο παρουσιάζονται οι επιπτώσεις των κεραυνών. Στο τρίτο κεφάλαιο αναλύονται τα δεδομένα που συλλέχθηκαν από τον ηλεκτρονικό κυρίως τύπο της χώρας, και τα οποία σχετίζονται με τους θανάτους και τους τραυματισμούς ανθρώπων, τους θανάτους ζώων, τις πυρκαγιές και τα πλήγματα σε εγκαταστάσεις, κτήρια και αεροπλάνα που οφείλονται σε πτώσεις κεραυνών για την χρονική περίοδο που εξετάστηκε. Τα στοιχεία έχουν κατανεμηθεί σε έτη, μήνες και ημέρες των συμβάντων. Επιπλέον, εισάγεται ο σχετικός συντελεστής θανάτων από κεραυνούς Dr, ο οποίος εκφράζει το σχετικό αριθμό θανάτων εξαιτίας κεραυνού σε μια χώρα ή περιοχή λαμβάνοντας υπ’ όψιν τον πληθυσμό, την έκταση και την δραστηριότητα των κεραυνών (Ng). Αυτός ο συντελεστής θα μπορούσε να είναι ένα κριτήριο για την αποτελεσματικότητα των μέτρων προστασίας από κεραυνούς, καθώς και για τα αποτελέσματα των εκπαιδευτικών και ενημερωτικών εκστρατειών για την προστασία από τους κεραυνούς. Από την ανάλυση των δεδομένων για τους θανάτους ανθρώπων εξαιτίας κεραυνού συμπεράναμε ότι έχουμε ένα μέσο όρο των 2,25 απωλειών ανά έτος (9 απώλειες συνολικά) και ότι το 77,8% των συμβάντων σημειώθηκαν κατά τους μήνες του μεσοκαλόκαιρου (Μάιος-Σεπτέμβριος), με τον Σεπτέμβριο να είναι ο μήνας με τα περισσότερα συμβάντα. Όσον αφορά τους τραυματισμούς από κεραυνικά πλήγματα, έχουμε ένα μέσο όρο των 3,75 τραυματιών ανά έτος, με το 40% των συμβάντων να τοποθετείται χρονικά κατά τη διάρκεια των μηνών του μεσοκαλόκαιρου, και με τον Νοέμβριο να είναι ο «χειρότερος», σε πλήθος περιστατικών, από τους δώδεκα μήνες. Κατά την τετραετή περίοδο καταγράφηκαν 979 θάνατοι ζώων σε μόλις 9 περιστατικά κεραυνικών πληγμάτων, με τον μέσο όρο να ανέρχεται σε 244,75 θανάτους ζώων ανά έτος. Το 60,2% των θανάτων αυτών σημειώθηκε τον Αύγουστο, ενώ συνολικά τους μήνες του μεσοκαλόκαιρου σημειώθηκε το 96,2% των θανάτων ζώων. Οι πυρκαγιές που σημειώθηκαν ήταν 45, αριθμός που αντιστοιχεί σε έναν μέσο όρο 11,25 πυρκαγιών ανά έτος, με το 62,2% αυτών να είναι δασικές. Το μεγαλύτερο ποσοστό των πυρκαγιών σημειώθηκαν κατά τους μήνες του μεσοκαλόκαιρου (73,4%). Ο μέσος όρος των πληγέντων εγκαταστάσεων από κεραυνό ανήλθε σε 9,5 ανά έτος (38 συμβάντα συνολικά), με τα περισσότερα περιστατικά να έχουν καταγραφεί τον Οκτώβριο. Τα κτήρια τα οποία επλήγησαν από κεραυνό ανήλθαν σε 23 με μέσο όρο 5,75 ανά έτος. Επιπλέον, καταγράφηκαν 5 κεραυνικά πλήγματα σε αεροσκάφη κατά την τετραετία που εξετάσθηκε, με το 80% των πληγμάτων να έχουν καταγραφεί κατά τους μήνες που έχουμε τις περισσότερες καταιγίδες στην Ελλάδα. Επίσης, έγινε η κατανομή των συμβάντων όλων των κατηγοριών στις ημέρες της εβδομάδος, χωρίς όμως να βγει κάποιο ενδιαφέρον συμπέρασμα. Τέλος, στο παράρτημα παρουσιάζονται λεπτομερώς τα συμβάντα, όπως καταγράφηκαν από την εκάστοτε πηγή. / This project presents the statistical analysis of lightning strikes in Greece over the last four years (2011-2014). The first chapter describes the phenomenon of lightning, types of lightning and its natural features, while the second chapter outlines the implications of lightning. The third chapter analyses the data, that were collected mainly from the country’s electronic media, concerning deaths, injuries, animal deaths, fires, strokes at facilities, structures and airplanes due to lightning for the time period examined. The data are based on distribution in years, months and days of occurrence. Furthermore, the relative lightning death indicator Dr is introduced, that expresses the relative number of lightning deaths in a country or region taking into account its population, its area and the lightning activity Ng. This indicator could be a criterion for the effectiveness of lightning protection, and for the outcomes of education and information campaigns for the protection from lightning. From the data analysis on lightning deaths we have concluded an average of 2.25 casualties per year (9 total loss) and that 77.8% of the incidents occurred during the months of Midsummer (May-September), with September being the month with most deaths. Regarding injuries from lightning strikes, we have an average of 3.75 injuries per year, while 40% of incidents have taken place during the months of Midsummer, and November being the "worst" of the twelve months in number of incidents. During the four-year period, 979 animal deaths were recorded in just 9 incidents of lightning strikes, with the average standing at 244.75 animal deaths per year. 60.2% of these deaths occurred in August, while during the months of Midsummer occurred 96.2% of total animal deaths. The fires that occurred were 45, corresponding to an average of 11.25 fires per year, with 62.2% of them being forest fires. The majority of fires occurred during the months of Midsummer (73.4%). The average of affected facilities from lightning reached 9.5 per year (38 incidents in total). The most incidents have been recorded on October. The structures which were hit by lightning amounted to 23 with an average of 5.75 per year. Moreover, 5 lightning strikes to aircraft were recorded over the four years examined, with 80% of these strikes occurring during the months that we have the most storms in Greece. The distribution of events of all categories in the days of the week is also presented, but we did not get to an interesting conclusion. Finally, in the annex the events are presented in details, as recorded by each source.
79

Laboratory study on lightning performance of dissipation devices

Mallick, Shreeharsh. January 2009 (has links)
Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.
80

The fractal nature of lightning an investigation of the fractal relationship of the structure of lightning to terrain /

Graham-Jones, Brian Clay. Hunter, Christopher. January 2006 (has links)
Thesis (M.S.)--Florida State University, 2006. / Advisor: Christopher Hunter, Florida State University, College of Arts and Sciences, Dept. of Mathematics. Title and description from dissertation home page (viewed Sept. 26, 2006). Document formatted into pages; contains ix, 122 pages. Includes bibliographical references.

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