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Some effects of ultrahigh frequency induced electrical currents on certain micro-organismsRabb, J. W. 07 November 2012 (has links)
High frequency induced electrical energy has been used by medical science for several years to produce heat internally in the human body. The uses of such a process are many and varied. They range all the way from producing artificial fever in the entire body to heating one certain afflicted spot such as a rheumatic joint. / Master of Science
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A Critique Of k-factor Method With Special Emphasis On Its ImplementationPradeep, A 09 1900 (has links) (PDF)
No description available.
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Degradation and recovery of polydimethylsiloxane (PDMS) based composites used as high voltage insulatorsAbraham Berhane, Teclesenbet 12 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Polydimethylsiloxane (PDMS) compounds are utilized in outdoor high voltage insulation
due to their low weight, vandalism resistance, better anti-contamination performance
and their superior hydrophobic nature. Under severe environmental conditions and over
prolonged service time, however, the hydrophobic surface can gradually become
hydrophilic and then recover with adequate resting period.
In this study, room temperature vulcanized (RTV) PDMS samples were prepared with
different formulations and then exposed to corona discharge to evaluate its effect. The
influence of different additives, such as different types and amount of fillers and
additionally added low molar mass silicone oils, on the hydrophobicity recovery of the
material was investigated. The effects of two types of corona treatment were also
evaluated.
Hydrophobicity recovery of corona and UV-C aged PDMS samples was evaluated by
means of static contact angle measurements.
Positron annihilation spectroscopy (PAS) gave important information on the micro
structural change after corona treatment of RTV PDMS as well as naturally aged high
temperature vulcanized (HTV) PDMS samples. The different formulations of the RTV
PDMS samples and the effect of the additives were studied with this technique. The
formation of a thin, highly crosslinked inorganic silica-like (SiOx) layer was confirmed
even at the early stage of degradation. It was also possible to estimate the thickness of
the silica-like layer formed during corona exposure that is responsible for the loss and
recovery of hydrophobicity.
The surface hardness and hydrophilicity change of PDMS samples due to corona
treatment were studied simultaneously with force distance measurements by atomic
force microscopy (AFM). The adhesive force calculated from the pull-off force-distance
curves showed that the adhesive force between the probe and the sample decreased
with increasing corona treatment time, indicating hydrophobicity recovery. In addition to
this, the increase in hardness after corona exposure provides indirect evidence of the
formation of a silica-like layer. In all cases the hydrophilicity and the surface hardness of
the PDMS samples increased directly after corona treatment and recovered with time.
Two types of FTIR spectroscopy were used to analyse the surface of the polymer. / AFRIKAANSE OPSOMMINGS: Polidimetielsiloksaan (PDMS) word in buitelug hoogspanninginsulasie gebruik as gevolg
van sy lae massa, weerstand teen vandalisme, verbeterde anti-kontaminasie
werkverrigting en superieure hidrofobiese karakter. Die hidrofobiese oppervlakte kan
egter gelydelik hidrofillies word onder uiterste omgewingsomstandighede en oor
langdurige dienstyd. PDMS materiaal herstel egter nadat dit genoeg rustyd toegelaat is.
Kamertemperatuur-gevulkaniseerde (KTV) PDMS met verskillende formulasies is in
hierdie studie voorberei, aan korona ontlading blootgestel, geëvalueer en vergelyk. Die
invloed van bymiddels soos verskillende tipes en hoeveelhede vuiler, asook addisionele
lae molekulêre massa silikoonolie, op die herstel van hidrofobisiteit van die materiaal is
ondersoek. Twee verskillende metodes van korona behandeling is ook geëvalueer.
Die herstel van hidrofobisiteit van korona en UV-C verouderde PDMS monsters is met
statiese kontakhoekmeting geëvalueer.
Positronvernietigingspektroskopie (PVS) is 'n kragtige tegniek wat belangrike inligting
oor die mikrostrukturele verandering van korona behandelde van KTV PDMS sowel as
natuurlik-verouderde hoë temperatuur gevulkaniseerde (HTV) PDMS monsters gee. Die
verskillende formulasies van die KTV PDMS monsters, sowel as die effek van die
vullers, is met behulp van hierdie tegniek ondersoek. Die vorming van 'n dun, hoogskruisgebinde,
anorganiese silika-agtige (SiOx) laag op die PDMS oppervlak, selfs
tydens die vroeë stadium van degradasie, is bevestig. Dit was ook moontlik om die dikte
van die silika-agtige laag wat gedurende die korona blootstelling gevorm het, en wat
verantwoordelik is vir die verlies aan hidrofobisiteit, te bepaal.
Die oppervlakhardheid en hidrofilisiteit verandering van PDMS monsters as gevolg van
korona behandeling, was gelyktydig met krag-afstand metings deur middel van
atoomkragmikroskopie (AKM) bestudeer. Die kleefkrag, soos bereken van aftrek kragafstandkurwes,
dui daarop dat kleefkragte tussen die taster en die monster afneem met
toenemende korona behandelingstyd, wat beduidend is op die herstel van
hidrofobisiteit. Daarbenewens is die toename van oppervlakhardheid na korona
blootstelling "n indirekte bewys van die formasie van 'n silika-agtige laag. In alle gevalle
het die hidrofilisiteit en die oppervlakhardheid van die PDMS monsters toegeneem direk
na afloop van korona behandeling en gevolglik herstel met tyd. Twee tipes IR spektroskopie metodes is gebruik vir die chemiese-oppervlak analises
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Partial discharge evaluation of a high voltage transformerKyere, Isaac Kwabena 02 1900 (has links)
M. Tech. (Power Engineering Department, Faculty of Engineering and Technology) -- Vaal University of Technology / This dissertation is devoted to the study of partial discharge evaluation of a high
voltage transformer. The 400 V/300 000 V (300 kV) high voltage transformer in the
high voltage laboratory was manufactured in 1967. Given the old age of the
transformer and the crucial importance of insulation systems, it is vital to assess the
condition of its insulation to ensure the effectiveness and the reliability of the
transformer as well as the safety of the personnel using it. In order to achieve that, it
is important to evaluate the partial discharge in the insulation system as this is the
main cause of destruction of insulation.
The phase-resolved partial discharge method was the main method used to perform
the partial discharge measurements in this research.
Partial discharge measurements were performed on a faulty 11 kV voltage
transformer. Defects were also created in samples of solid insulation at predetermined
locations with different shapes and sizes. The measurements taken on the
11 kV voltage transformer and samples of solid insulation formed a basis to prove
the validity of the assessment methods on the 300 kV transformer.
Using the method mentioned above, partial discharges were recorded with respect to
the phase of the applied voltage with the aid of a commercial instrument which
complies with IEC 60270, (ICM monitor - partial discharge detector from Power
Diagnostix Systems GmbH).
The observations from this study have furthered the understanding of partial
discharge processes. The patterns recorded were analysed in order to conclude about
the condition of the transformer. From the partial discharge pattern, the type and
location of partial discharges were concluded. The patterns obtained from the
transformer reveal that the device is healthy and can be operated up to 200 kV.
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Non-conventional methods for energy extraction from high voltage transmission linesNicolae, Dan Valentin 06 1900 (has links)
Thesis (D. Tech. Electrical engineering) --Vaal University of Technology / A comprehensive study upon "Non-conventional methods for energy extraction from the high voltage transmission lines" was addressed in this thesis. As defined in this study, a non-conventional method to extract energy is one that does not touch the conductors of the line. The theoretical framework which originated in the Maxwell's equations was presented as a base for discussion of all the methods and the conditions for the extraction to be possible. This study presents various methods such as capacitive and inductive to extract energy from high voltage alternating current transmission lines (HVAC). Although in theory, for high voltage direct current transmission lines (HVDC), the conditions for extraction are not matched, there remain some methods that could still attract interest. The centre point of this thesis is the new power application of the Rogowski coil. This method is analysed in full extent starting from theoretical modelling, computer simulations, design of the actual Rogowski coil and power electronics associated with it, and experimental results on a reduced scale model. In doing this, strong mathematical tools and computer software such as Matlab 6, Quick Field and MathCAD were used. At the end of this thesis, some conclusions are presented together with new ideas for further research in the field.
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In-service condition monitoring of polymer housed surge arrester within eThekwini ElectricityGumede, Makhosonke January 2015 (has links)
Submitted in fulfillment of the requirements for the degree of Master in Technology, Durban University of Technology, Durban, South Africa, 2015. / The primary objective of this research was to investigate the failures occurring in the family of surge arresters used within EThekwini Electricity, making use of different diagnostic methods, such as leakage current testing (LC), infrared scanning (IR), and partial discharge (PD) measurements. The different diagnostic tests were used to assess the degradation process of the polymer housed surge arresters and their failure.
The measurements were used for diagnosis of 120 kV/65 kA surge arresters of different brands. Tests were performed on surge arresters that were still in the system and these test results were compared with results from tests performed on failed units. Results obtained from the different tests were compared to the test results for different families or designs. An imperfect arrester will exhibit excessive heating when an electrical surge is discharged. The aforementioned tenets are the primary factors influencing degradation and causing failure of Metal Oxide Surge Arrester (MOSA) in a system.
These factors can decrease creepage and flashover distance on insulation, which could result in a substantial increase in resistive leakage current, (which is a few microamperes in ideal condition), overheating, and PD formation on the zinc oxide varistor element. Therefore, it is extremely important to assess the status of the surge arresters whilst they are in service, firstly so that they can be removed from the system before they fail and, and secondly, to verify their condition, and their ability to effectively protect the substation apparatus.
Using infrared inspection, valuable information of condition of surge arresters was obtained, heat inside the surge arresters was detected and this shows that IR analysis can therefore be considered as an additional method to assess the condition of polymer housed surge arresters. It was observed that partial discharge activity is an indication of degradation in arrester varistor. LC test, IR, and PD measurement were valuable in obtaining sufficient information for failure of surge arresters. In additional, during the visual internal inspection of arresters, evidence of punctures, treeing, tracking, and moisture masks were noted on ZnO blocks and seals. These results indicate that the moisture ingress through the sealing collar can cause unnecessary outages. / M
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Comparison of the lightning performance between the poles of the Cahora-Bassa ±533 kV HVDC linesStrelec, Gavin Jason January 2016 (has links)
This work contributes toward research in the field of lightning performance of High Voltage Direct Current (HVDC) transmission lines, focusing on the impact of the line polarity on the incidence of line faults. Although there has been some recent research into the influence of polarity, there appears to be no confirmed effect that might influence the design of new lines. The research presents an investigation into the lightning performance of the two poles of the Cahora-Bassa HVDC transmission line. In order to compare the performance of the two polarities, the average lightning exposure over an 8-year period was confirmed to be very similar for both lines. Lightning stroke data from the South African Lightning Detection Network was correlated with fault times from the transmission-line protection scheme. The classification of the lightning related faults was used to determine the relative performance of the two poles, particularly in relation to polarity, and to infer if there was any influence of polarity on the lightning attachment process. This investigation for the Cahora-Bassa scheme shows that twenty-three out of twenty-five lightning related faults occurred on the positive pole. The results concur with performance experience on several HVDC lines from China and Canada, which indicate that lightning related faults favour the positive pole by a ratio of between 8:1 and 10:1. This represents a valuable contribution, which substantiates that HVDC line polarity has an influence on the lightning attachment process, and indicates that there is a need to re-examine the lightning shielding design for HVDC transmission lines. / GS2016
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High-voltage-enabled operational amplifier and active-decoupling technique for wideband balun-LNALiu, Miao January 2011 (has links)
University of Macau / Faculty of Science and Technology / Department of Electrical and Computer Engineering
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A computer-aided measurement system for monopolar high-voltage direct-current coronating lines湯世傑, Tong, Sai-kit. January 1986 (has links)
published_or_final_version / Electrical Engineering / Master / Master of Philosophy
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Μελέτη υπερτάσεων σε δίκτυα χαμηλής τάσης εξοπλισμένα με απαγωγούς υπέρτασηςΜεταξάς, Αλέξανδρος 09 October 2014 (has links)
Αυτή η διπλωματική εργασία πραγματεύεται την διάδοση κρουστικών υπερτάσεων που προκαλούνται από κεραυνικά πλήγματα σε ένα δίκτυο χαμηλής τάσης, στο οποίο βρίσκονται εγκατεστημένοι απαγωγοί υπέρτασης. Σκοπός της διπλωματικής εργασίας είναι η εξαγωγή χρήσιμων συμπερασμάτων σχετικά με την προστασία που παρέχουν οι απαγωγοί σε ένα τέτοιο δίκτυο, μέσω αποτελεσμάτων που θα προκύψουν από προσομοιώσεις. / This diploma thesis deals with the propagation of impulse overvoltages caused by lightning strikes in a low voltage network, which is supllied with surge protective devices (SPDs). The goal of this thesis is the extraction of useful conclusions regarding the protection that SPDs can offer to such a network, by comparing various results that arise from simulations.
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