Дисертації з теми "The current distribution"
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1
EL-Rashid, Jihad, and Youssef Tawk. "Current Distribution in High RF Power Transistors." Thesis, University of Gävle, Ämnesavdelningen för elektronik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-5735.
Повний текст джерелаАнотація:
To obtain the power levels required from high RF power transistors, the size of the chip has often to be made so large that inductance of electrical connections inside the package cannot be neglected. This may have the effect that various parts of the transistor chip are not connected exactly parallel, i.e. drain and gate voltages and currents densities will not be the same on different parts of the chip. This may result in degraded output power and efficiency. The same effect may occur when more than one chip are connected in parallel in a transistor package to obtain even higher output power.Often the connections to the transistor package are approximated as a number of electrical point connections (normally three: gate, drain, source); meaning that each of them can be described by a single electrical potential and current. In reality, they may be large enough that voltage and current distributions have to be considered. These distributions will be affected by different mountings of the transistor and other connected components.In this work, the LDMOS power transistor MRF6S21140HR3 was modeled using the segmentation method in high frequency signal simulation HFSS which is a 3D Full-Wave Electromagnetic Field Simulation, and utilized the advanced design system ADS to find a parameterized lumped model. Both the electromagnetic and lumped models showed consistent results. Non-ideal parallel connection of sub-transistors on chip is very important, but further studies are needed for definite conclusion. It was verified through modeling that non ideal parallel connection of different chips in the package does have an effect; the effect however is quiet small which proves that the signal is slightly non-uniformly distributed between the three chips in the package. External connection to PCB (drain connection is considered in this work) can effectively be taken as a point connection to some approximation. The electrical behavior of the modeled transistor was studied through the design of a class B power amplifier in order to estimate the importance of performance degradation due to non-ideal parallel connections and how these non ideal connections degrade efficiency and output power. The modeled transistor can deliver a maximum output power of 147 watts and efficiency of 65%. We have also studied the current distribution between the three chips in a three stage class B power amplifier. Again, the difference in the current distribution between the three chips turned out to be quiet small. All these results are presented through this work. The final conclusion regarding the current distribution between multichips cannot be made just based on these simulation results. The next step should be aimed at considering other effects, the thermal effect for example, in order to know exactly whether it is uniformly or not uniformly distributed.
2
Smith, Daniel Allen. "Current distribution at varing frequencies in hybrid /." Connect to online version at Digital.Maag, 1999. http://hdl.handle.net/1989/4789.
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3
Ferri, Matthew A. (Matthew Anthony). "Current distribution in cable-in conduit superconductors." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28111.
Повний текст джерелаАнотація:
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994, and Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (p. 101-103).
by Matthew A. Ferri.
M.S.
4
Johnston, Martin David. "Current and field distribution in high temperature superconductors." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298870.
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5
Wei, Xingguo. "Current distribution materials for solid oxide fuel cells." Thesis, Imperial College London, 2004. http://hdl.handle.net/10044/1/11527.
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6
Gokgoz, Sinan. "A Stand-alone Induction Powered Current And Current Harmonics Measurement System For Distribution Lines." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614967/index.pdf.
Повний текст джерелаАнотація:
The presence of information and communication technologies in the field of energy is increasing every day. Smart grid subject which aims to increase the percentage of energy generation through renewable resources and to make consumers to be involved in grid actively, is gaining importance day by day. In order to provide an effcient and reliable operation of smart grid network, it is necessary to collect relevant parameters from network components via communication infrastructure and to evaluate collected information. Also, with the inclusion of distributed energy sources in the power lines, collection of relevant data becomes important in order to ensure the quality of power. In the scope of this study, to measure current parameters, two DSP based electronic circuits and necessary embedded software have been developed. Data acquisition card is a fixed device which is to be installed to a point on the power line to gather current value samples. By means of being fed through magnetic induction from the line, this part of the system could stay on-line permanently and this allows taking measurements on demand. Sampling of line current is performed through principle of magnetic induction from the line on current sensing instrument which is connected to data-acquisition part. Also by utilization of clamp-on instruments, cutting of energy lines is not needed. Samples received by control card over radio frequency or infrared communication, are evaluated with the help of Discrete Fourier Transform (DFT). Control card can show information about Root mean square (RMS) value and harmonic components of line current and total harmonics distortion (THD) on graphic LCD. Present state of the system was tested in LV and MV environments and shown to be used on distribution lines. The system presented in this study is open to improvements and suggestions to make the system to be able to work on high voltage lines are made.
7
Tidd, Chad N. "Hardware model of a shipboard Zonal Electrical Distribution System (ZEDS) Alternating Current/Direct Current (AC/DC)." Thesis, Cambridge Massachusetts Institute of Technolog, 2010. http://hdl.handle.net/10945/4936.
Повний текст джерелаАнотація:
CIVINSApproved for public release; distribution is unlimited
A hardware model of a shipboard electrical distribution system based on aspects of the DDG 51 Flight IIA, Arleigh Burke class, 60Hz Alternating Current (AC) and the future direct current (DC), zonal electrical distribution system (ZEDS). These distribution boards were designed and built for the purpose of testing electrical system components at the Massachusetts Institute of Technology's Laboratory for Electromagnetic and Electronic Systems (LEES). Two 5 kW generators serve as electrical generation for the ZEDS benchtop emulator boards. The hardware models support experimentation with AC and DC ZEDS power loading and protection. The hardware models reflect the AC ZEDS architecture employed on the DDG-51 class destroyers. The emulator is a three phase electrical system with both port and starboard buses, a computer interface to control the generators and contactors or solid state relays through a graphic user interface (GUI). The system is capable of being configured and operated in a split plant, parallel or single generator plant configuration.
8
Tidd, Chad N. (Chad Norman). "Hardware model of a shipboard zonal electrical distribution system (ZEDS) : alternating current/direct current (AC/DC)." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61908.
Повний текст джерелаАнотація:
Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M. in Engineering and Management)--Massachusetts Institute of Technology, Engineering Systems Division, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 91-92).
A hardware model of a shipboard electrical distribution system based on aspects of the DDG 51 Flight IIA, Arleigh Burke class, 60Hz Alternating Current (AC) and the future direct current (DC), zonal electrical distribution system (ZEDS). These distribution boards were designed and built for the purpose of testing electrical system components at the Massachusetts Institute of Technology's Laboratory for Electromagnetic and Electronic Systems (LEES). The combination of existing electrical generators and the newly created electrical distribution boards will provide a hereto unattained level of access for testing and evaluating a number of research topics currently being worked on at LEES. The level of reality inherent in this system will enable the user to refine experimental hardware and software in a safe and controlled environment. The user will benefit from a quicker product development process. Additionally, the ability to easily produce verifiable records to demonstrate the effectiveness/applicability of their individual experiments will help to progress research at LEES along the product development path. Two 5 kW generators serve as electrical generation for the ZEDS benchtop emulator boards. The hardware models support experimentation with AC and DC ZEDS power loading and protection. The hardware models reflect the AC ZEDS architecture employed on the DDG-51 class destroyers. The emulator is a three phase electrical system with both port and starboard buses, a computer interface to control the generators and contactors or solid state relays through a graphic user interface (GUI). The system is capable of being configured and operated in a split plant, parallel or single generator plant configuration.
by Chad N. Tidd.
S.M.in Engineering and Management
Nav.E.
9
Byrne, Philip. "Mathematical modelling and experimental simulation of chlorate and chlor-alkali cells." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3182.
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Ajitkumar, Rohit. "An analysis of DC distribution systems." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39590.
Повний текст джерелаАнотація:
The Master's Thesis research focuses on analyzing the possibilities of using Direct Current distribution systems to distribute power to end users. Considering the shift in load types in the past few decades and also a growing demand of distributed generation, DC distribution can potentially offer higher efficiencies and cost savings to utilities. The incorporation of DC distribution offers the opportunity to eliminate multiple conversion stages for devices which are powered using DC electricity. The integration of power sources such as photovoltaics and fuel cells, which produce DC power, offer further incentives to consider the use of DC systems. Using DC systems can help eliminate the conversion losses associated with rectifiers and inverters which would be part of the infrastructure if AC distribution was used. In the literature, the study of DC distribution has been limited to customized systems. The objective of this research is to analyze DC distribution when applied to systems based on standard IEEE test feeder systems. The IEEE 13 node test feeder and the IEEE 37 node test feeder will be used as the basis for the analysis. Issues such as associated costs, protection and integration of appliances will also be addressed.
11
Hofmann, Markus Hans [Verfasser]. "Current distribution in parallel-connected battery cells / Markus Hans Hofmann." München : Verlag Dr. Hut, 2020. http://d-nb.info/1222353199/34.
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12
Mahmood, Humam S. "Modelling tertiary current distribution in electrodeposition cells with flowing electrolytes." Thesis, London South Bank University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.618650.
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13
Hellal, Abdelhafid. "An analytical study of back-to-back HVDC link in weak AC systems /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65466.
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14
Moraes, Edison Pires de. "Distribuição de corrente entre semicondutores em retificadores de alta corrente - estudo de casos reais." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/3/3143/tde-29012009-114411/.
Повний текст джерелаАнотація:
Nos processos industriais envolvendo eletrólise, como na produção de alumínio, cobre, zinco, níquel, manganês, carbeto de silício, cloro e seus derivados, as correntes envolvidas em geral atingem patamares que excedem o valor nominal de um único semicondutor, exigindo a associação de componentes em paralelo com uma distribuição de corrente equilibrada. Este trabalho apresenta uma análise comparativa da distribuição de corrente em associações de semicondutores em paralelo em vinte retificadores de alta potência com diferentes tipos de arquitetura física de barramentos. A particularidade deste estudo é a medição simultânea das correntes em todos os semicondutores de todos os ramos do retificador obtendo-se uma imagem da distribuição real de correntes do conversor.The industrial electrolytic processes to produce, aluminum, cooper, zinc, nickel, manganese, silicon carbide, chlorine and its derivative, require current values which greatly exceed the capability of single rectifying devices and paralleled combinations of semiconductors or equipments are necessary. This study evaluated through a comparative analyzes twenty rectifiers, with different busbar geometries, in order to verify the current distribution in paralleled devices. The differential of this study is the simultaneous measurement of currents in all semiconductors of each branch in order to obtain a real representation of the rectifiers current distribution.
15
Tsemekhman, Kiril. "Current distribution and density of states in the quantum hall effect /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9737.
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16
Tsemekhman, Vadim. "Charge relaxation, current distribution, and breakdown of the quantum Hall effect /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9739.
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17
Proctor-Williams, Kerry. "Dosage and Distribution in Morphosyntax Intervention: Current Evidence and Future Needs." Digital Commons @ East Tennessee State University, 2009. https://dc.etsu.edu/etsu-works/1773.
Повний текст джерелаАнотація:
This article reviews the effectiveness of dose forms and the efficacy of dosage and distribution in morphosyntax intervention for children. Dose forms include the commonly used techniques, procedures, and intervention contexts that constitute teaching episodes; dosage includes the quantitative measures of dose, dose frequency, total intervention duration, and cumulative intervention intensity (S. F. Warren, M. E. Fey, & P. J. Yoder, 2007). Based on the literature, this article first outlines and evaluates the range of dose forms and intervention contexts that clinicians and researchers can employ to facilitate morphosyntactic acquisition. Then, it defines and evaluates research outcomes and provides examples of the dosage components. Current evidence, which focuses primarily on young children and early-developing morphology and sentence structures, suggests that some dose forms and dosage levels are more effective with some populations and some morphosyntactic forms than with others. Distributed practice within sessions and throughout the total period of treatment appears to be more facilitative than massed practice, at least for children with typical language development. The scant research concerning total intervention duration suggests that it affects children's developmental trajectory and that treatment attendance matters. What is missing from the research base is detailed information about the effectiveness and efficacy of intervention for the acquisition of particular morphosyntactic forms in specific populations. The article summarizes these gaps in 3 research goals that reflect the argument of S. F. Warren et al. that it is time to conduct systematic comparisons of specific dose forms while testing how each measure of dosage affects outcomes.
18
Omar, Kaashif A. M. "Electromagnetic flyer plate technology and development of a novel current distribution sensor." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/17740.
Повний текст джерелаАнотація:
The development of both experimental and diagnostic equipment to assist with simulating the mechanical effects of cold X-ray deposition is covered by this work. This thesis reviews the various experimental techniques suitable for conducting the electromagnetic launch of flyer plates and the chosen technique is developed into a fully functional experimental facility. The development of a bespoke 1-dimensional computer model is also described in the text. A novel current distribution measurement technique is also fully described. This new diagnostic approach will allow the variation of the current across the width of a large conductor to be easily determined which is something not previously demonstrated.
19
Lalander, Emilia, Mårten Grabbe, and Mats Leijon. "On the velocity distribution for hydro-kinetic energy conversion from tidal currents and rivers." Uppsala universitet, Elektricitetslära, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-195499.
Повний текст джерелаАнотація:
Tidal currents and rivers are promising sources of renewable energy given that suitable turbines for kinetic energy conversion are developed. To be economically and technically feasible, a velocity distribution that can give a high degree of utilization (or capacity factor), while the ratio of maximum to rated velocity is low would be preferable. The rated velocity is defined as the velocity at which rated power is achieved. Despite many attempts to estimate the resource, however, reports on the possible degree of utilisation from tidal currents and rivers are scarce. In this paper the velocity distribution from a number of regulated rivers, unregulated rivers and tidal currents have been analysed regarding the degree of utilisation, the fraction of converted energy and the ratio of maximum to rated velocity. Two methods have been used for choosing the rated velocity; one aiming at a high fraction of converted energy and one aiming at a high degree of utilisation. Using the first method, with a rated velocity close to the maximum velocity, it is unlikely that the turbine will reach the cut-out velocity. This results in, on average, a degree of utilisation of 23% for regulated rivers, 19% for unregulated rivers and 17% for tidal currents while converting roughly 30-40% of the kinetic energy. Choosing a rated velocity closer to the mean velocity resulted in, on average, a degree of utilisation of 57% for regulated rivers, 52% for unregulated rivers and 45% for tidal currents. The ratio of maximum to rated velocity would still be no higher than 2.0 for regulated rivers, 1.2 for unregulated rivers and 1.6 for tidal currents. This implies that the velocity distribution of both rivers and tidal currents is promising for kinetic energy conversion. These results, however, do not include weather related effects or extreme velocities such as the 50-year velocity. A velocity factor is introduced to describe what degree of utilisation can be expected at a site. The velocity factor is defined as the ratio U-max/U-rate at the desired degree of utilisation, and serves as an early indicator of the suitability of a site.
20
Perrot, Fabrice. "The effects of multi-current impulses on the low current bulk distribution in varistor materials, under continuous AC operation." Thesis, University of Brighton, 1995. https://research.brighton.ac.uk/en/studentTheses/0c2ff4b0-630d-41b1-8241-658d582ac6d5.
Повний текст джерелаАнотація:
The first part of this work gives a broad introduction on the origins of ZnO bismuthbased v aristor materials. The electrical properties of ZnO varistors follow, giving a detailed and up to date review of all the models published with an attempt to explain their complex conduction mechanisms. Stresses found in HV networks are also reviewed in detail, their knowledge being necessary to link the de gradation and fail ure mechanisms of ZnO varistors which are explained at depth. The manufacture of ZnO varistors on a laboratory scale is also presented: disc type as well as thick-film type varistors were manufactured and tested during this inv estigation. The parameters influencing the microstructure and electrical characteristics of varistors during sintering were reviewed. Testing sequences used by manufacturers as well as surge arrester testing standards were also assessed to derive tests for the laboratory produced samples.
21
Isik, Mehmet. "Thermally Stimulated Current Study Of Traps Distribution In Beta-tlins2 Layered Crystals." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609667/index.pdf.
Повний текст джерелаАнотація:
Trapping centres in as-grown TlInS2 layered single crystals have been studied by using a thermally stimulated current (TSC) technique. TSC measurements have been performed in the temperature range of 10-300 K with various heating rates. Experimental evidence has been found for the presence of five trapping centres with activation energies 12, 14, 400, 570 and 650 meV. Their capture cross-sections and concentrations were also determined. It is concluded that in these centres retrapping is negligible as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. An exponential distribution of traps was revealed from the analysis of the TSC data obtained at different light excitation temperatures.
The transmission and reflection spectra of TlInS2 crystals were measured over the spectral region of 400-1100 nm to determine the absorption coefficient and refractive index. The analysis of the room temperature absorption data revealed the coexistence of the indirect and direct transitions. The absorption edge was observed to shift toward the lower energy values as temperature increases from 10 to 300 K. The oscillator and the dispersion energies, and the zero-frequency refractive index were also reported. Furthermore, the chemical composition of TlInS2 crystals was determined from energy dispersive spectroscopic analysis. The parameters of monoclinic unit cell were found by studying the x-ray powder diffraction.
22
Nasser, Hisham. "Thermally Stimulated Current Study Of Traps Distribution In Tlgases Layered Single Crystals." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611866/index.pdf.
Повний текст джерелаАнотація:
Trapping centres and their distributions in as-grown TlGaSeS layered single
crystals were studied using thermally stimulated current (TSC) measurements.
The investigations were performed in the temperature range of 10&ndash160 K with various heating rates between 0.6&ndash
1.2 K/s. Experimental evidence has been found for the presence of three electrons trapping centres with activation energies 12, 20, and 49 meV and one hole trapping centre located at 12 meV. Their capture cross-sections and concentrations were also determined. It is concluded that in these centres retrapping is negligible as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. The optical properties of TlGaSeS layered single crystals have been investigated by measuring the transmission and the reflection in the wavelength region between 400 and 1100 nm. The optical indirect transitions with a band gap energy of 2.27 eV and direct transitions with a band gap energy of 2.58 eV were found by analyzing the absorption data at room temperature. The rate of change v of the indirect band gap with temperature was determined from the transmission measurements in the temperature range of 10&ndash
300 K. The oscillator and the dispersion energies, the oscillator strength, and the zero-frequency refractive index were also reported. The parameters of monoclinic unit cell and the chemical composition of TlGaSes crystals were found by X-ray powder diffraction and energy dispersive spectroscopic analysis, respectively.
23
Wurjantara, Wisnu. "Computation of current distribution in long elliptic conductors using Mathieu functions expansion." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq28693.pdf.
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24
King, Andrew Luke. "Iron distribution and phytoplankton iron limitation in the southern California Current System." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3306532.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed June 16, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
25
Zainal, Abidin Ilham Mukriz. "Modelling and experimental investigation of eddy current distribution for angular defect characterisation." Thesis, University of Newcastle Upon Tyne, 2011. http://hdl.handle.net/10443/1308.
Повний текст джерелаАнотація:
Current industrial requirements for nondestructive testing demand defect quantification rather than simple defect detection. This is not a simple task as defects in components, such as cracks, rarely have a simple geometrical shape. Therefore, the influence of defect shape and orientation and its effect on the inspection results needs to be addressed to avoid misinterpretation of the response signals and for a quantitative characterisation of defects. Finite element method (FEM) numerical simulations for eddy current non-destructive evaluation (ECNDE) can provide information on how the induced eddy current interacts with defects and the effect of defect shape and geometry towards the results. Through the analysis of the simulation results, links can be established between the measurements and information relating to the defect, such as 3-D shape, size and location, which facilitates not only forward problem but also inverse modelling involving experimental system specification and configuration; and pattern recognition for 3-D defect information. This work provides a study of the characterisation of angular defects through the technique of visualisation and mapping of magnetic field distribution for pulsed eddy current (PEC) and temperature distribution for PEC thermography. 3-D FEM simulations are utilised to provide the guidelines for experimental designs and specifications; understanding of the underlying physics surrounding a particular defect; and means for features extraction from the acquired responses. Through the study, defect Quantitative Non-destructive Evaluation (QNDE) has been established using the features extracted from the mapping by taking into consideration the angular characteristic of defect in the inspection results. Experimental investigations are then performed to verify the simulation results and the feasibility of the proposed techniques and extracted features to be used in acquiring information about the angular defect. The work concludes that the technique of mapping the resultant distribution from the interaction of eddy currents and defects has provided the vital information needed for defect characterisation. Features extracted from the mapping via numerical investigations have provided the means for the QNDE of angular defects. The work shows that the technique and features introduced has provided an alternative way for defect characterisation and QNDE, which also can be extended its application to other industrial components and research field.
26
Potter, Marcus Jason. "Parametric analysis of a solid polymer fuel cell using current distribution mapping." Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/19470.
Повний текст джерелаАнотація:
During operation of the solid polymer fuel cell (SPFC). its performance is limited by the concentrations of hydrogen and oxygen at the reaction interfaces and in most SPFC designs, the hydration state of the membrane. Since in general, the concentrations of water and the gaseous species vary along the flow channel, the performance is also likely to change along the flow channel. In order to study this phenomenon, a measurement system was developed to map the current distribution across the electrode surface. The current distribution has been measured by dividing one of the current collectors into a number of electrically isolated segments. The current flowing through each of the segments was measured while maintaining a constant potential across the surface of the gas diffusion layer. Two separate segmented current collectors were developed. The first was used to measure the current distribution for an 80 cm2 single cell, and the second was used to investigate the local current densities around a single flow channel. The effects of the feed gas humidities on the spatial current density in the 80 cm2 fuel cell were investigated for two different membrane-electrode configurations. With Nafion 117 as electrolyte and at a cell temperature of 80°C. the membrane was found to dehydrate in the initial portion of the gas flow channel when the relative humidity of both the hydrogen and oxygen feed gases was less than 50%. With a Gore-Select membrane electrode assembly (hydrogen and air. temperature- 60°C). the membrane was sufficiently hydrated at all feed gas humidification conditions. The performance of the cell was found to deteriorate at higher feed gas humidities as a result of the lower partial pressures of the reactant gases. Measurements of the effects of gas pressures, stoichiometries and humidities on the length-wise and width-wise perfonnance around a single flow channel (Gore-Select membrane electrode assembly) are discussed in relation to a gas flow model.
27
Ferri, Matthew A. (Matthew Anthony). "Current distribution and stability criteria for superconducting cables in transient magnetic fields." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10406.
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28
Motloung, Rethabile Frangenie. "Understanding current and potential distribution of Australian acacia species in southern Africa." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/79720.
Повний текст джерелаАнотація:
This dissertation presents research on the value of using different sources of data to
explore the factors determining invasiveness of introduced species. The research draws upon
the availability of data on the historical trial plantings of alien species and other sources. The
focus of the study is on Australian Acacia species as a taxon introduced into southern Africa
(Lesotho, South Africa and Swaziland). The first component of the study focused on
understanding the factors determining introduction outcome of species in historical trial
plantings and invasion success of Australian Acacia species using Species Distribution
Models (SDMs) and classification tree techniques. SDMs were calibrated using the native
range occurrence records (Australia) and were validated using results of 150 years of South
African government forestry trial planting records and invaded range data from the Southern
African Plant Invaders Atlas. To understand factors associated with survival (‘trial success’)
or failure to survive (‘trial failure’) of species in historical trial plantings, classification and
regression tree analysis was used. The results indicate climate as one of the factors that
explains introduction and/or invasion success of Australian Acacia species in southern Africa. However, the results also indicate that for ‘trial failures’ there are factors other than climate
that could have influenced the trial outcome. This study emphasizes the need to integrate data on whether the species has been recorded to be invasive elsewhere with climate matching for
invasion risk assessment.
The second component of the study focused on understanding the distribution patterns of
Australian Acacia species that are not known as invasive in southern Africa. The specific
aims were to determine which species still exist at previously recorded sites and determine
the current invasion status. This was done by collating data from different sources that list
species introduced into southern Africa and then conducting revisits. For the purpose of this
study, revisits means conducting field surveys based on recorded occurrences of introduced
species. The known occurrence data for species on the list were obtained from different data
sources and various invasion biology experts. As it was not practical to do revisits for all
species on the list, three ornamental species (Acacia floribunda, A. pendula and A. retinodes)
were selected as part of the pilot study for the conducted revisits in this study. Acacia
retinodes trees were not found during the revisits. The results provided data that could be
used to characterize species based on the Blackburn et al., (2011) scheme. However, it is not clear whether observed Acacia pendula or A. floribunda trees will spread away from the sites
hence the need to continuously monitor sites for spread. The methods used in this research
establish a protocol for future work on conducting revisits at known localities of introduced
species to determine their population dynamics and thereby characterize the species
according to the scheme for management purposes.Dissertation (MSc)--University of Pretoria, 2014.
National Research Foundation (NRF)
Zoology and Entomology
MSc (Zoology)
Unrestricted
29
Mushagala, Jimmy Matabaro. "Harmonic analysis and effectiveness of mitigation techniques applied to a bipolar HVDC system." Thesis, Cape Peninsula University of Technology, 2017. http://hdl.handle.net/20.500.11838/2461.
Повний текст джерелаАнотація:
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2017.High Voltage Direct Current (HVDC) transmission is a safe and efficient technology designed to deliver large amounts of electrical power over long distances with minimal losses and at low costs. HVDC links require converters and filters at both terminal stations. The core component of the HVDC system is the power converter that connects the DC and AC systems together. The conversion from AC to DC, and vice versa, is achieved mainly through electronic switches called thyristors. The thyristor-based Line Commutated Converter (LCC) is a mature and trusted technology for HVDC transmission throughout the world. HVDC converters are bidirectional and can function in either rectification (AC to DC) or inversion mode (DC to AC). This is achieved when the voltage polarity across the converter gets swapped by the controllers, because current cannot change its direction in thyristors. In this thesis an analytical model of the HVDC converters is developed in the frequency domain by modelling it in DIgSILENT. The objective is to study the harmonics induced to the AC side from HVDC converters. Therefore, it is important in the real world to understand the principles, what causes harmonics to be generated in HVDC and transferred to the HVAC system. The objective of this thesis is to investigate the effectiveness of mitigation techniques used, on how they reduce harmonics by keeping these harmonic levels within specified values admissible by international standards (e.g. IEEE, etc).
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Fonseca, Marco Filipe Matos da. "Integrating wind generation in the distribution network." Master's thesis, Faculdade de Ciências e Tecnologia, 2012. http://hdl.handle.net/10362/8187.
Повний текст джерелаАнотація:
Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Energias Renováveis – Conversão Eléctrica e Utilização SustentáveisOne of the current challenges the electricity grid has is to actively connect future generation to its network without the need to fully reinforce it. This dissertation will study the use of dynamic ratings on overhead lines to increase its capacity and thus defer major investment on infrastructure reinforcement. The amount of current an overhead line can withstand in a given time is defined by the distance towards the ground, which is proportional to the conductor´s temperature, which is given by a static rating stated in the P27 standard – “Current Rating Guide for High Voltage Overhead Lines Operating in the UK Distribution System”. This rating changes from season to season and depends on specific values for ambient temperature, wind speed, wind direction and the probability that in a year the conductor exceeds its design temperature. This standard is seen as being very restrictive and a limiting factor on overhead line capacity for both future generation connections and demand. Wind speed and direction are extremely important on the cooling of overhead lines and in times of strong winds the conductor cools down, allowing extra amount of current to flow through it. By using real time weather data, it´s possible to obtain the maximum current that can flow in an overhead line for a specific operating temperature and assess the amount of headroom possible given by the difference between the static ratings and the new dynamic ratings is assessed. A view on the extra amount of energy produced, as well as CO2 emission savings and profit will also be presented, giving a practical result by applying dynamic ratings.
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Hölling, Matthias. "Adaptive current and voltage measurement device for low voltage distribution in power nets /." [S.l.] : [s.n.], 2000. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=13985.
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Olesen, Ole Berdiin. "Smarter Fault Localization in Distribution Systems : A Self-Sustained Sensor for Current Measurement." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-27227.
Повний текст джерелаАнотація:
This thesis deals with the development of self-sustained sensors based on non-conventional measurement techniques. The motivation behind this topic is to help utility companies reduce their fault handling time and improve the way faults are handled. As of today, the distribution system does not have widespread surveillance and automation systems in place. The thesis therefore investigates a sensor design based on Rogowski coils (RC), with both measurement and power supply capabilities.The concept of printed-circuit-board Rogowski coils (PCB RC) and conventional RCs for current measurement is presented. A theoretical, dimensional study with respect to feasibility and output signal magnitude is then performed. On basis of this analysis, a PCB RC prototype is manufactured. For the sensor to be implemented in the resonance grounded distribution system, it must be able to measure currents of low magnitude, as the fault current is compensated by Petersen coils. The prototype is therefore tested for common distribution system current values. Due to limitations during construction and design flaws, the PCB RC performance was poor. The induced voltage error, with respect to the theoretical response was 64.3 - 69.1 %.As the prototype's ability to supply enough power to the sensor circuitry (demand found to be > 10 mW) proved so limited, a more thorough analysis concerning the RC is presented. Obtaining this amount of power is, theoretically possible and easier with a conventional RC. Its maximum average power supply capability was found to be 10.4 mW during ideal conditions. Even better results can probably be obtained as well. Based on this RC, the complete sensor system is discussed. This include rectification, digitizing, integration and boosting of the RC voltage to 3 V for battery application. A survey of possible fault localization methods for resonance grounded distribution systems is presented and an implementation is suggested.Finally, the prototype is tested with short circuit currents of 30 kA amplitude. The performance was better than for the load current test, but the magnitude error was still substantial. It varied from 20 % to 40 %. However, the lab's signal integration showed that the prototype reproduced the applied current waveform accurately.The simulations, testing and analysis performed indicate that a RC can be used for both supply of power and measurements. However, a prototype should be manufactured in order to assess this thesis' theoretical results. Combined with the proposed auxiliary circuitry and implementation strategy, it can improve the utility's fault handling.
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Wang, Hongjie. "Design and Control of Series Resonant Converters for DC Current Power Distribution Applications." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7160.
Повний текст джерелаАнотація:
With the growth of renewable energy usage and energy storage adoption in recent decades, people have started to reevaluate the possible roles of dc systems in current and future electrical systems. The dc voltage distribution has been applied in various applications, such as data centers and aircraft industry, for high efficiency and power density. However, for some applications such as subsea gas and oil fields, and ocean observatory systems, the dc current distribution is preferred over dc voltage distribution for its low cost and robustness against cable faults. Design and control of dc power distribution systems for different applications is an emerging research area with complex technical challenges. This dissertation solves the technical challenges in analysis, design, modeling, control and protection of series resonant converters (SRCs) for dc current distribution applications. An optimum design that has high efficiency, high reliability, and minimum required control efforts for the SRC with constant input current has been achieved and demonstrated by applying the analysis and design procedures developed in this dissertation. The modeling and analysis presented in this dissertation represents an operating condition that has not been studied in the literature and could be easily extended to other resonant converter topologies. Explicit analytical expressions have been provided for all key transfer functions, including input impedance and control-to-output, offering valuable resources to design feed-back regulation and to evaluate system stability. Based on the control strategies and control design presented in this dissertation, stable and reliable operation of dc current distribution systems with long distance cable has been achieved and demonstrated. The proposed analysis, design procedure, stability evaluation, control strategy and protection techniques in this dissertation can be applied to a wide range of similar scenarios as well, which greatly increases their value.
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Pillar, Stanley C. "Distribution and population dynamics of Euphausia lucens (Euphausiacea) in the southern Benguela current." Doctoral thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/8406.
Повний текст джерелаАнотація:
Bibliography: leaves 182-196.The thesis first reviews the research on zooplankton ecology in the Benguela system and then evaluates the contribution of euphausiids to the zooplankton biomass of the southern Benguela region. The study further investigates the population dynamics and maintenance of the dominant euphausiid, Euphausia lucens, principally in the St Helena Bay region because of its importance as a recruitment area for the pelagic fishery.
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Hall, David Eric. "Transient thermal models for overhead current-carrying hardware." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/17133.
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Higier, Andrew Michael. "An In-Situ and Ex-Situ Investigation of Current Density Variations in a Proton Exchange Membrane Fuel Cell." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/373.
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In polymer electrolyte membrane (PEM) fuel cells one of the most important components is the flow field. The flow field distributes reactant gasses to the active area and also delivers electrons from the outer circuit so that the electrochemical reaction may be completed. Optimizing flow field design is extremely important in order to increase the overall power density of the fuel cell. It is particularly important to understand the ways in which the different portions of the flow field, namely the land and channel sections, interact with the gas diffusion layer (GDL), catalyst layer and membrane; this study focuses on those interactions. The most common type of flow field design currently used in PEM fuel cells is the serpentine flow field. It is used for its simplicity of design, its effectiveness in distributing reactants and its water removal capabilities. The knowledge about where current density is higher, under the land or the channel, is critical for flow field design and optimization. Yet, no direct measurement data are available for serpentine flow fields. In this study a fuel cell with a single channel serpentine flow field is used to separately measure the current density under the land and channel, which is either catalyzed or insulated on the cathode. In this manner, a systematic study is conducted under a wide variety of conditions and a series of comparisons are made between land and channel current density. Results show that under most operating conditions, current density is higher under the land than that under the channel. However, at low voltage, a rapid drop off in current density occurs under the land due to concentration losses. The mechanisms for the direct measurement results and general guidelines for serpentine flow field design and optimizations are provided. In addition the same technique is utilized to separately measure current density under the land and channel on a variety of serpentine flow field geometries. Each flow field is tested under a wide variety of operating conditions thereby providing guidance for the optimum design geometry. Experimental results show that generally flow fields with both thinner lands and thinner channels provide better overall performance. However, the optimal flow field designs are highly dependent on fuel cell operating parameters. Finally, it is critical not only to know where the current density is greater, under the land or under the channel, but to understand the fundamental mechanisms driving these differences. Resistance was measured, ex-situ, between the GDE and flow plate under the land of the flow field and under the channel separately. The contact resistance between the gas diffusion electrode (GDE) and the graphite flow plate were measured using an ex-situ technique. The resistance was measured under different land and channel widths. Cyclic Voltammetry tests were also conducted in order to determine if there is any different in electrochemically active area(ECA) under the land and under the channel and what the cause of this difference might be. Results show that the compression of the gas diffusion electrode not only affects the electronic resistance but the ECA as well and that these are key factors in current density variations under the land and channel.
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Crego, Ramiro Daniel. "Modeling the distribution of meadows in arid and semi-arid Patagonia, Argentina: assessing current distribution and predicting response to climate change." OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/1001.
Повний текст джерелаАнотація:
Meadows are critical in arid and semi-arid Argentinean Patagonia because of their importance for regional biodiversity. Despite this, little information on the spatial distribution of meadows is available and no analysis of the potential effect of climate change on meadows has been performed, which hampers conservation planning. In this study, I modeled the spatial distribution of meadows and investigated how climate change may affect the current distribution of meadows in arid and semiarid Patagonia by 2050. In addition, I investigated conservation status and areas of desertification vulnerability of those areas predicted to contain meadows. I used high-resolution imagery available in Google Earth software to visually estimate presence and absence of meadows. To model current and future distribution of meadows I used these observations and different socio-environmental predictor variables. I implemented generalized linear, additive, boosting, and random forest models, as the basis for a mean ensemble technique. I predicted future distribution of meadows using four different general circulation models and the A2 SERES scenario. The final ensemble model was an accurate representation of the current distribution of meadows in Patagonia and indicates they are severely under-represented within protected areas. I determined that overall meadow abundance is going to decrease by 2050 given the changes in climate. However, there were two contrasting trends: severe reduction of meadows in northwest Patagonia and Tierra del Fuego Island, and an expansion of suitable areas for meadows in the south and a small section in the northwest. This first regional map of meadow distribution across Argentinean Patagonia and information on meadows vulnerability to climate change represent key information for planning actions to conserve this critical habitat.
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Zhang, Lu. "Development of LCL DC/DC transformer and fault current limiting LCL VSC converter for high power DC networks." Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=211240.
Повний текст джерелаАнотація:
In order to satisfy the huge demand energy transmission in future, the DC grid concept is proposed based on voltage sourced converter (VSC) HVDC and modular multilevel converter (MMC) HVDC technologies. It provides an attractive approach for long distance power transmission such as offshore renewable energy transmission in Europe. However, there are two main obstacles in the DC grid development. The first obstacle is the DC fault detection and selective isolation. Under severe fault condition, the DC grid is desired to isolate the healthy and faulty part which implies the whole grid system will operate normally during the fault. The second obstacle is the voltage stepping in DC grid system. The high power converter is desired to achieve high voltage stepping ratio yet must be cost-effective. In this thesis, an IGBT-based DC/DC converter employing an internal inductor-capacitor-inductor (LCL) passive circuit is presented to overcome above two obstacles. The proposed converter can achieve high voltage stepping without internal AC transformer implying smaller converter size and it is also designed to have reasonable efficiency in high power application. In addition, the converter has good response even under extreme fault conditions. The IGBT-based LCL DC/DC converter design procedure and performance under fault condition is investigated based on the theoretical studies initially. The converter is modelled on PSCAD platform under normal/fault operation and the simulation results are used for converter efficiency calculation and fault analysis. The advantages of IGBT-based LCL DC/DC converter are demonstrated by comparing with other two high power DC/DC converter topologies. A low power level prototype of LCL DC/DC converter is built following the design principle. The hardware results are used to verify the theoretical conclusions. The VSC converter is defenceless to DC faults in DC grid application. In order to overco The VSC converter is defenceless to DC faults in DC grid application. In order to overcome this major drawback, a fault tolerant VSC converter employing LCL passive circuit is studied in this thesis. The LCL VSC converter design principle is presented by analysing the converter equations. The converter model is developed on PSCAD platform under normal/fault operation. An advanced control method is designed based on developed MATLAB analytical model to improve the LCL VSC converter stability. The advantages of LCL VSC converter are presented by comparing with its performance with conventional L-VSC converter considering efficiency and fault response. A fault tolerant DC grid topology employing LCL VSCs and using low speed protection is also investigated in this thesis. The simple mechanical DC circuit breakers are used at DC bus bars and at connecting points of each DC cable. A comprehensive protection scenario including DC cable differential protection, DC bus bar protection and back up protection is employed to protect the whole DC grid against any probable DC faults. An accurate DC cable model is adopted for a four-terminal DC grid which is modelled on PSCAD platform. The advantage and feasibility of this method in DC fault protection is investigated based on the developed grid model.
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Antaloae, C. C. "Feasibility of high frequency alternating current power distribution for the automobile auxiliary electrical system." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/6792.
Повний текст джерелаАнотація:
This study investigates the feasibility and potential benefits of high frequency
alternating current (HFAC) for vehicle auxiliary electrical systems.
A 100Vrms, 50kHz sinusoidal AC bus is compared with 14V DC and 42V DC electrical
systems in terms of mass and energy efficiency. The investigation is focused on the four
main sub-systems of an on-board electrical network, namely: the power generation,
power distribution, power conversion and the electrical loads. In addition, a systemlevel
inquiry is conducted for the HFAC bus and a comparable 42V DC system.
A combination of computer simulation, analytical analysis and experimental work has
highlighted benefits for the HFAC power distribution sub-system and for low-torque
motor actuators. Specifically, the HFAC conductor mass is potentially 70% and 30%
lighter than comparable 14V DC and 42V DC cables, respectively. Also, the proposed
cable is expected to be at least 80% more energy efficient than the current DC
conductor technology. In addition, it was found that 400Hz AC machines can
successfully replace DC motor actuators with a rated torque of up to 2Nm. The former
are up to 100% more efficient and approximately 60% lighter and more compact than
the existing DC motors in vehicles. However, it is argued that the HFAC supply is not
feasible for high-torque motor actuators. This is because of the high energy losses and
increased machine torque ripple associated with the use of HFAC power.
The HFAC power conversion sub-system offers benefits in terms of simple power
converter structure and efficient HFAC/DC converters. However, a significant limitation
is the high power loss within HFAC/AC modules, which can be as high as 900W for a
2.4kW load with continuous operation. Similar restrictions are highlighted for the
HFAC power generation sub-system, where up to 400W is lost in a 4kW DC/HFAC
power module.
The conclusion of the present work is that the HFAC system offers mass and energy
efficiency benefits for the conventional vehicle by leveraging the use of compact lowtorque
motor actuators and lightweight wiring technology.
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Vestgöte, Karl. "Quantum Key Distribution - current state of the technology and prospects in the near future." Thesis, Linköping University, Department of Electrical Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-17579.
Повний текст джерелаАнотація:
The thesis presents the basics of Quantum Key Distribution, a survey of the present techniques, a look at the possible future, and finally a comparison to the alternative technique of using public key or manual distribution of keys.
Techniques to integrate QKD with the existing telecom fiber infrastructure have been studied, and so has the EU-funded project SECOQC.
Last the security and efficiency of QKD have been examined, with focus on what level of security that is required, existing security solutions have been used as a comparison.
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Mehra, Arun 1967. "An approximate method for determining the frequency dependent current distribution in a ground plane." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278176.
Повний текст джерелаАнотація:
This MS thesis proposes a methodology to compute a frequency dependent current distribution for a ground plane with the ultimate aim of utilizing this current distribution to compute the plane parasitics. A iterative finite differencing technique is utilized to solve a two dimensional diffusion equation for the current distribution on the plane. Starting with an initial DC current density over the entire plane grid, the frequency dependent current density is obtained by imposing the necessary boundary conditions and allowing the current to redistribute itself over the plane. An iterative procedure based on simultaneous over relaxation is employed to get faster convergence. This method takes into account the presence of sources, sinks and holes on the plane. Finally the plane parasitics are computed using integral methods and energy considerations.
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Behlman, Nicholas James. "Electron Energy Distribution Measurements in the Plume Region of a Low Current Hollow Cathode." Digital WPI, 2010. https://digitalcommons.wpi.edu/etd-theses/72.
Повний текст джерелаАнотація:
A hollow cathode is an electron source used in a number of different electric thrusters for space propulsion. One important component of the device that helps initiate and sustain the discharge is called the keeper electrode. Cathode keeper erosion is one of the main limiting factors in the lifetime of electric thrusters. Sputtering due to high-energy ion bombardment is believed to be responsible for keeper erosion. Existing models of the cathode plume, including the OrCa2D code developed at Jet Propulsion Laboratory, do not predict these high-energy ions and experimental measurement of the electron energy distribution function (EEDF) could provide useful information for the development of a high fidelity model of the plume region. Understanding of the mechanism by which these high-energy ions are produced could lead to improvements in the design of hollow cathodes. The primary focus of this work is to determine the EEDF in the cathode plume. A single Langmuir probe is used to measure the current-voltage (I-V) characteristic of the plasma plume from a low current hollow cathode in the region downstream of the keeper orifice. The EEDF is obtained using the Druyvesteyn procedure (based on interpretation of the second derivative of the I-V curve), and parameters such as electron temperature, plasma density and plasma potential are also obtained. The dependence of the EEDF and other parameters on the radial position in the plume is examined. Results show that the EEDF deviates from the Maxwellian distribution, and is more accurately described by the Druyvesteyn distribution directly downstream of the cathode. Off-axis measurements of the EEDF indicate the presence of fast electrons, most likely due to the anode geometry. The cathode used in these tests is representative of the cathode used in a 200W class Hall thruster. Data is presented for a hollow cathode operating on argon gas for two cases with different discharge currents.
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Mokhlesi, Javad, and Saman Lohrasebi. "The Current State and Future Trends in The Use of Pallets in Distribution Systems." Thesis, Högskolan i Borås, Institutionen Ingenjörshögskolan, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-19689.
Повний текст джерелаАнотація:
Pallets play a very important role in whole distribution systems through the supply chain. Such a fact alone shows the importance of pallets in today’s fast growing global logistics. Due to the increasing number of regulations and policies regarding natural resource conservations and also sustainable development, the issue of pallet utilization, reuse and recycling matters became the core concern in most of the researches performed in this field.As a consequence, the presented report discusses the current problems, requirements and debates around pallets utilization in distribution systems in depth along with the other affecting factors such as Cost, Environment, Materials, Sustainability, Information Technology and so forth. To achieve such goals, the first step is recognizing the mass Industrial production factors and global market requirements for the current and future of pallet utilization in order to achieve the desired efficiency and effectiveness in practice with focus on standardized pallets utilization in specific regions like European Union.The second step is the considering of various pallet types compatibility in different environments with respect to unit load assignments both at present and future. The third step is to challenge the obtained data and observed results and also, to verify them according to the foreseen future requirements, tendencies and demands of pallets and unit loads assignments through the international logistics providers. The last step which is as well the most important part of this thesis report is, to put the information together in order to clarify and specify the encountered difficulties regarding usage of pallets with concentration on cost, environment and ergonomic issues.
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Botes, Lizeth. "Taxonomy, distribution and toxicity of dinoflagellate species in the southern Benguela current, South Africa." Doctoral thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/6236.
Повний текст джерелаАнотація:
Bibliography: leaves 165-184.The threat of harmful algal blooms with their attendant problems, exists throughout the Benguela region. In the southern Benguela upwelling system, water discolorations, referred to as 'red tides', are common and usually attributed to dinoflagellate species. The first aim of the thesis was to investigate the taxonomy of gymnodinioid species in the southern Benguela current. In order to investigate the morphology of the southern Benguela isolates, a simple and rapid scanning electron microscope preparative technique was developed. In the course of these studies, a new genus and new species were identified and described.
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Verma, Manish. "A comprehensive overview, behavioral model and simulation of a Fault Current Limiter." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/33841.
Повний текст джерелаАнотація:
Distribution systems across most parts of the globe are highly radial in nature. As loads are gradually increased on a particular distribution system, a higher operating current state leading to increased fault current levels is attained. Hence, the relay co-ordination is disturbed and equipments such as feeders and circuit breakers need to be replaced with higher rating so that they can handle the new currents often leading to expensive retrofit costs.
The use of fault current limiter (FCL) is proposed to mitigate the effects of high current levels on a distribution system. A comprehensive and up-to-date literature review of FCL technologies is presented. Detailed efforts of an in-house developed behavioral superconducting FCL model are delineated, including FCL control algorithm and its implementation in PSCAD®/EMTDC environment. Results from simulation studies are investigated and compared to an actual FCL commissioned by Z-energy to highlight the effectiveness of a generic model without having to access proprietary details. Extending those concepts, a solid-state and hybrid type of limiter is also modeled and it results discussed. Finally, an impact assessment is conducted on the distribution protection scheme, due to the FCL being inserted and subsequently operated in the distribution system.Master of Science
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Pokrovskiy, S., I. Rudnev, A. Podlivaev, and M. Osipov. "Method and Experimental Setup for the Study of the Local Current Distribution in Conducting Micro-and Nanostructures." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35220.
Повний текст джерелаАнотація:
The method for the study of the spatial distribution of current in micro-and nanostructures on the
measured magnetic field is presented. The methods of studies the magnetic field distribution of conducting
nanostructures by passing a transport current are considered. The technique of current recovery from experimental
data is offered.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35220
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Verdin, Baptiste. "Etude d'électrodes grande surface d'électrolyseurs PEM : inhomogénéités de fonctionnement et intégration de catalyseurs innovants." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS036/document.
Повний текст джерелаАнотація:
La production d’hydrogène par électrolyse de l’eau PEM prendra une place importante dans le paysage énergétique pour le stockage des EnR. Le changement d’échelle nécessaire ne peut s’envisager que par une augmentation significative de la puissance nominale, passant essentiellement par l’accroissement de leur taille et de la densité de courant. Dans ces conditions, un fonctionnement optimal et une durée de vie suffisante ne pourront être obtenus que par l’homogénéisation de la répartition du courant à la surface des électrodes. Au cours de cette thèse, nous avons utilisé pour la première fois un outil de cartographie des distributions de courant et de température à la surface d’AME grande surface, issus d’un design industriel. Une carte de mesure S++® conçue sur mesure et adaptée à l’utilisation envisagée a été intégrée à une monocellule PEM de 250cm². Une caractérisation électro-mécanique de la cellule a mis en évidence le lien existant entre le champ de forces de compression mécanique et de la densité de courant. Nous montrons qu’une compression mécanique optimale n’est pas suffisante pour homogénéiser la distribution de courant : le design de cellule, et plus particulièrement la distribution des fluides, joue un rôle majeur dans l’inhomogénéité de la distribution de courant, récurrente entre le centre et la périphérie de la cellule. Nous soulignons la concentration des lignes de courant vers le centre de l’AME lors de tests dynamiques, conséquence d’un vieillissement spatialement différencié. Nous avons également développé une structure d’électrode permettant de ré-homogénéiser globalement la distribution de courant, ce qui permet un meilleur maintien des performances dans le temps. Nous avons également développé un modèle numérique de la couche catalytique permettant de mieux comprendre la répartition des lignes de courant en fonction des caractéristiques géométriques des collecteurs poreux. Nous mettons en lumière le rôle majeur des surtensions dans le pouvoir répartiteur de la couche active, qui est particulièrement faible côté cathodique. Nous préconisons de densifier la couche catalytique pour une meilleure répartition du courant et pour limiter les différenciations locales de vieillissement. L’ensemble des observations en mono cellule a été confirmé par des essais sur un stack commercialHydrogen production from PEM water electrolysis will take a great place in the energy landscape for RES storage. This scale shift requires a significant increase of the nominal power, and therefore an increase in size and a gain in the current density. Optimal operation (in terms of efficiency and lifetime) can be obtained only if the distribution of current lines over the electrode surface is adequately homogeneous. In this thesis, we have used for the first time a specific tool for the in-situ mapping of current and temperature in a large surface area PEM single cell. A customized S++® measuring plate, adapted to our application, has been implemented in a 250cm² PEM single cell. Electromechanical characterization of the cell has put into evidence the link between the field of clamping force and the local current density. We have shown that an optimal mechanical compression is not sufficient to homogenize current distribution. We have demonstrated that the cell design, in particular the fluid distribution, plays a major role in current distribution inhomogeneities, which recurrently form between the center and the periphery of the cell. We have also shown that during dynamic operation, current lines tend to concentrate at the center of the cell as a consequence of spatially differentiated ageing. We have developed an electrode structure that facilitates the global re-homogenization of current lines and additionally shows an increased durability. In parallel, we have developed a numerical model to calculate the distribution of current lines within the thickness of catalytic layers as a function of the geometry of the PTL. We have found that overvoltages play a major role in current distribution, and that the cathode is prone to more heterogeneities. We propose to densify the catalyst layers for a better current repartition and a lesser differentiated ageing. Key findings from single cell tests have been confirmed on a commercial stack
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Blasi, Bronson Richard. "DC microgrids: review and applications." Kansas State University, 2013. http://hdl.handle.net/2097/16823.
Повний текст джерелаАнотація:
Master of ScienceDepartment of Architectural Engineering and Construction Science
Fred Hasler
This paper discusses a brief history of electricity, specifically alternating current (AC) and direct current (DC), and how the current standard of AC distribution has been reached. DC power was first produced in 1800, but the shift to AC occurred in the 1880’s with the advent of the transformer. Because the decisions for distribution were made over 100 years ago, it could be time to rethink the standards of power distribution. Compared to traditional AC distribution, DC microgrids are significantly more energy efficient when implemented with distributed generation. Distributed generation, or on-site generation from photovoltaic panels, wind turbines, fuel cells, or microturbines, is more efficient when the power is transmitted by DC. DC generation, paired with the growing DC load profile, increases energy savings by utilizing DC architecture and eliminating wasteful conversions. Energy savings would result from a lower grid strain and more efficient utilization of the utility grid. DC distribution results in a more reliable electrical service due to short transmission distances, high service reliability when paired with on-site generation, and efficient storage. Occupant safety is a perceived concern with DC microgrids due to the lack of knowledge and familiarity in regards to these systems. However, with proper regulation and design standards, building occupants never encounter voltage higher than 24VDC, which is significantly safer than existing 120VAC in the United States. DC Microgrids have several disadvantages such as higher initial cost due, in part, to unfamiliarity of the system as well as a general lack of code recognition and efficiency metric recognition leading to difficult certification and code compliance. Case studies are cited in this paper to demonstrate energy reduction possibilities due to the lack of modeling ability in current energy analysis programs and demonstrated energy savings of approximately 20%. It was concluded that continued advancement in code development will come from pressure to increase energy efficiency. This pressure, paired with the standardization of a 24VDC plug and socket, will cause substantial increases in DC microgrid usage in the next 10 years.
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Yu, Jianghui. "DC Fault Current Analysis and Control for Modular Multilevel Converters." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/78054.
Повний текст джерелаАнотація:
Recent research into industrial applications of electric power conversion shows an increase in the use of renewable energy sources and an increase in the need for electric power by the loads. The Medium-Voltage DC (MVDC) concept can be an optimal solution. On the other hand, the Modular Multilevel Converter (MMC) is an attractive converter topology choice, as it has advantages such as excellent harmonic performance, distributed energy storage, and near ideal current and voltage scalability.
The fault response, on the other hand, is a big challenge for the MVDC distribution systems and the traditional MMCs with the Half-Bridge submodule configuration, especially when a DC short circuit fault happens. In this study, the fault current behavior is analyzed. An alternative submodule topology and a fault operation control are explored to achieve the fault current limiting capability of the converter.
A three-phase SiC-based MMC prototype with the Full-Bridge configuration is designed and built. The SiC devices can be readily adopted to take advantage of the wide-bandgap devices in MVDC applications. The Full-Bridge configuration provides additional control and energy storage capabilities. The full in-depth design, controls, and testing of the MMC prototype are presented, including among others: component selection, control algorithms, control hardware implementation, pre-charge and discharge circuits, and protection scheme.
Systematical tests are conducted to verify the function of the converter. The fault current behavior and the performance of the proposed control are verified by both simulation and experiment. Fast fault current clearing and fault ride-through capability are achieved.Master of Science
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Monzon, Jorge Emilio. "Current density distribution versus frequency and current for metal electrodes." 1986. http://catalog.hathitrust.org/api/volumes/oclc/14923364.html.
Повний текст джерелаАнотація:
Thesis (M.A.)--University of Wisconsin--Madison, 1986.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 11-13).