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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.
51

Numerical Aspects of Image Rendering using Spherical Harmonics

Gyllensten, Johan January 2009 (has links)
Image rendering is the process of creating realistic computer images from  geometric models and physical laws of light and reflection. This master thesis deals mainly with the numerical intricacies of implementing an image renderer using spherical harmonics. It investigates how to calculate the reflection of light in a surface using the Phong model, and employs ray tracing to create a realistic image of a geometric model. Further, it investigates different ways of calculating the spherical harmonic representation of a function defined on the sphere. The thesis also deals with the implementation of self-shadowing, and the effects of adding this component to the rendering equation.
52

Allocating Power Quality Monitors in Electrical Distribution Systems to Measure and Detect Harmonics Pollution

Alhazmi, Yassir 20 May 2010 (has links)
The growth of non-linear devices has increased the harmonics pollution in distribution systems. Under industrial competition, the concern over power quality, especially harmonic distortion, has increased due to the new generation of load equipment. This equipment has been fully automated electronically, so it is very sensitive to any power quality disturbances. Electrical power organizations have set standards to limit the harmonics pollution in the distribution systems; however, the enforcement of the standards has to be disciplinal, by applying a penalty fee for any customer or utility that exceeds the standard limits. In order to apply the penalty fee properly, precise detection of harmonics pollution sources must be considered. The bus voltages and the line currents in the entire system have to be known in order to obtain accurate identification, which can be achieved by monitoring the distribution system. The large number of sensors needed to monitor the distribution system increases the cost of the monitoring system; therefore, the sensors have to be installed in an optimum way that decreases their quantity and their construction fixed costs. This thesis offers a new optimization approach for allocating the monitors in the distribution system. The Vertex-Colouring approach reduces the monitoring system cost by placing the harmonics pollution monitors in minimum cost locations where they can observe all the buses and branches of the distribution system. The number of monitors is affected by the percentage of nonlinear loads in the distribution network; thus, investigations on lightly polluted systems, medium polluted systems, and heavily polluted systems have been presented. The relation between the harmonics pollution level from one side, and the nonlinear load types, power ratings, and voltage levels from the other side has been highlighted as important observations of the polluted systems investigation. The Total Harmonic Powers (THP) method has been used to identify the harmonics pollution sources. In addition to its simplicity, The THP method is efficient, and requires the network voltage and current values which can be provided by the proposed monitoring system. The ability to apply the THP method on any distribution system has been scrutinized in order to confirm its validity for distribution systems.
53

Effects of Power System Harmonics on Distribution Transformer Insulation Performance

Hamid, Muhammad 23 September 2011 (has links)
Floating feeder resonances are one of the new challenges being put forward by the renewable energy based distributed generation (DG) installations. Generally, the harmonic injection from DGs are within IEEE standard 519-1992 limits. Although the harmonics are within the IEEE limits, they are a potential threat to power equipment’s insulation system integrity due to floating feeder resonances. There is a reasonable probability that at some point in time the feeder resonant frequency may coincide with one of the injected harmonics. Such phenomenon amplifies the specific harmonic causing additional stress on the equipment’s insulation system. In this thesis a feeder resonance study is done on the IEEE 34 bus distribution feeder to show the resonance shift problem in a DG loaded distribution feeder. Electric field study is then carried out on transformer winding to assess the dependence of electric field on harmonic distortion. At first the acoustic emission (AE) technique is employed to identify the change in the electric field distribution inside the winding at higher frequency. The AE technique together with the acoustic waveguide is utilized to locate the partial discharges under power frequency and high frequency operation. The results show a change in partial discharge (PD) location, which implies that the electric field redistributes in the transformer winding at higher frequency In order to further understand the electric field distribution, a high voltage air core coil is modeled by R, L and C ladder network. The R, L and C parameters are solved by finite element method and finally the electric field is calculated by computing the node potentials in the ladder network at various frequencies. The electric field results show that at high frequency distortion the electric stress enhances between fourth and fifth layer of the winding which may give rise to a PD activity; hence degrading the insulation. An aging experiment is also performed to understand the impact of high frequency distortion on transformer paper insulation. Paper samples are taken from a field aged transformer. They are aged for 72 hours under power frequency and various distorted waveforms. Dissipation factor is used as a comparison tool for paper samples before and after aging. Results show that paper samples aged under distorted waveforms showed a double increase in dissipation factor compared to the samples aged under power frequency.
54

The fifteen-cent guitar re-tempering the standard six-string guitar /

Swoger-Ruston, John Paul. January 2000 (has links)
Thesis (M.A.)--York University, 2000. Graduate Programme in Music. / Typescript. Includes bibliographical references (leaves 108-111). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ59201.
55

Theory and estimation of acoustic intensity and energy density /

Thomas, Derek C., January 2008 (has links) (PDF)
Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2008. / Includes bibliographical references (p. 79-82).
56

Probabilistic analysis of harmonics in railway traction system

阮國豪, Yuen, Kwok-hoo. January 2000 (has links)
published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy
57

Allocating Power Quality Monitors in Electrical Distribution Systems to Measure and Detect Harmonics Pollution

Alhazmi, Yassir 20 May 2010 (has links)
The growth of non-linear devices has increased the harmonics pollution in distribution systems. Under industrial competition, the concern over power quality, especially harmonic distortion, has increased due to the new generation of load equipment. This equipment has been fully automated electronically, so it is very sensitive to any power quality disturbances. Electrical power organizations have set standards to limit the harmonics pollution in the distribution systems; however, the enforcement of the standards has to be disciplinal, by applying a penalty fee for any customer or utility that exceeds the standard limits. In order to apply the penalty fee properly, precise detection of harmonics pollution sources must be considered. The bus voltages and the line currents in the entire system have to be known in order to obtain accurate identification, which can be achieved by monitoring the distribution system. The large number of sensors needed to monitor the distribution system increases the cost of the monitoring system; therefore, the sensors have to be installed in an optimum way that decreases their quantity and their construction fixed costs. This thesis offers a new optimization approach for allocating the monitors in the distribution system. The Vertex-Colouring approach reduces the monitoring system cost by placing the harmonics pollution monitors in minimum cost locations where they can observe all the buses and branches of the distribution system. The number of monitors is affected by the percentage of nonlinear loads in the distribution network; thus, investigations on lightly polluted systems, medium polluted systems, and heavily polluted systems have been presented. The relation between the harmonics pollution level from one side, and the nonlinear load types, power ratings, and voltage levels from the other side has been highlighted as important observations of the polluted systems investigation. The Total Harmonic Powers (THP) method has been used to identify the harmonics pollution sources. In addition to its simplicity, The THP method is efficient, and requires the network voltage and current values which can be provided by the proposed monitoring system. The ability to apply the THP method on any distribution system has been scrutinized in order to confirm its validity for distribution systems.
58

Spherical harmonic specification of certain atmospheric forcing functions.

Pitcher, Eric John January 1970 (has links)
No description available.
59

Harmonic analysis of power systems connected to converter substations

Christoforidis, George P. 05 1900 (has links)
No description available.
60

Effects of Power System Harmonics on Distribution Transformer Insulation Performance

Hamid, Muhammad 23 September 2011 (has links)
Floating feeder resonances are one of the new challenges being put forward by the renewable energy based distributed generation (DG) installations. Generally, the harmonic injection from DGs are within IEEE standard 519-1992 limits. Although the harmonics are within the IEEE limits, they are a potential threat to power equipment’s insulation system integrity due to floating feeder resonances. There is a reasonable probability that at some point in time the feeder resonant frequency may coincide with one of the injected harmonics. Such phenomenon amplifies the specific harmonic causing additional stress on the equipment’s insulation system. In this thesis a feeder resonance study is done on the IEEE 34 bus distribution feeder to show the resonance shift problem in a DG loaded distribution feeder. Electric field study is then carried out on transformer winding to assess the dependence of electric field on harmonic distortion. At first the acoustic emission (AE) technique is employed to identify the change in the electric field distribution inside the winding at higher frequency. The AE technique together with the acoustic waveguide is utilized to locate the partial discharges under power frequency and high frequency operation. The results show a change in partial discharge (PD) location, which implies that the electric field redistributes in the transformer winding at higher frequency In order to further understand the electric field distribution, a high voltage air core coil is modeled by R, L and C ladder network. The R, L and C parameters are solved by finite element method and finally the electric field is calculated by computing the node potentials in the ladder network at various frequencies. The electric field results show that at high frequency distortion the electric stress enhances between fourth and fifth layer of the winding which may give rise to a PD activity; hence degrading the insulation. An aging experiment is also performed to understand the impact of high frequency distortion on transformer paper insulation. Paper samples are taken from a field aged transformer. They are aged for 72 hours under power frequency and various distorted waveforms. Dissipation factor is used as a comparison tool for paper samples before and after aging. Results show that paper samples aged under distorted waveforms showed a double increase in dissipation factor compared to the samples aged under power frequency.

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