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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.
31

Analysing the propagation of fast time-varying electromagnetic disturbances along power-transmission structures

Sinclair, Andrew John 28 August 2012 (has links)
D.Ing. / The propagation of fast disturbances along power transmission structures depends on the parameters of the excitation for the disturbance, the characteristics of the power transmission structure, and eventually on the characteristics of the electrical load connected to the structure. This thesis will therefore target the determination of the parameters of transmission structures in Chapter 2, applicable transmission-line theory in Chapter 3, modelling the load in Chapter 4, and apply this knowledge to the specific problem of over-voltages on the terminals of machines fed via cables from inverters in Chapter 5. The rest of this chapter is devoted to explaining the introductory aspects of this application problem.
32

A multiphase harmonic load flow solution technique

Xu, Wenyuan January 1990 (has links)
This thesis presents a comprehensive solution technique for power system harmonic analysis with unbalanced load flow conditions. It is based on multiphase modelling of the system in phase quantities. Two of the most important features of this technique are the multiphase approach to the harmonic load flow problem, and the capability to add component nonlinearities easily. The first feature allows the technique to be used for either single-phase or three-phase, and for either balanced or unbalanced harmonic analysis. The second feature allows the later addition of power electronic device models. The technique is simple in concept. The nonlinear elements are first modelled as harmonic Norton equivalent circuits based on the network load flow conditions. These linear circuits are then included in the network solution with multiphase load flow constraints and network unbalances. Once the new load flow solutions are obtained, improved Norton equivalent circuits can be calculated, which in turn are used for improved network solutions. The entire solution scheme is therefore iterative, and stops when certain convergence criteria are met. The unbalanced harmonics from nonlinear inductors, synchronous machines and static compensators with thyristor-controlled reactors are studied in this thesis. The convergence properties of the technique are investigated with test cases and theoretical analysis. In addition to the harmonic load flow analysis, this technique can also be used as an improved initialization procedure for the Electromagnetic Transient Program (EMTP). / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate
33

An analytical investigation of stress waves in power-transmission chains /

Davidson, Joseph Killworth January 1965 (has links)
No description available.
34

A multi-agent based approach to transmission cost allocation

Yan, Yonghe., 嚴勇河. January 2000 (has links)
published_or_final_version / Computer Science and Information Systems / Doctoral / Doctor of Philosophy
35

Modelling of distorted electrical power and its practical compensation in industrial plant

Pretorius, Jan Harm Christiaan 27 August 2012 (has links)
D.Ing. / Alternating current systems employing single-frequency sinusoidal waveforms render optimal service when the currents in that system are also sinusoidal and have a fixed phase relationship to the voltages that drive them. Under unity- power factor conditions, the currents are in phase with the voltages and optimal net-energy transfer takes place under minimum loading conditions, i.e. with the lowest effective values of current and voltage in the system. The above conditions were realised in the earlier years, because supply authorities generated 50 Hz sinusoidal voltages and consumers drew 50 Hz sinusoidal currents with fixed phase relationships to these voltages. Static and rotating electrical equipment like transformers, motors, heating and lighting equipment were equally compatible with this requirement and well-behaved AC networks were more the rule than the exception. The fact that three-phase systems conveyed the bulk of the power from one topographical location to the next did not constrain the utilisation of that concept at all, even though poly-phase transmission systems were necessary to increase the economy of transmission and to furnish non-pulsating power transfer. Also, additional theory had to be developed to handle unbalanced conditions in these multi-phase systems and to take care of complex network analysis and fault conditions. Difficulties begin to manifest themselves when equipment not meeting these requirements is connected to the network and when the currents it draws are not sinusoidal. An increasing number of applications demand DC-voltage supplies from which DC-currents are to be drawn. Because power transmission is carried out by means of AC networks, the DC is furnished by converting or rectifying the AC-supply. Power-electronic circuits, of which the R 2P2 power supplies the AEC employs are no exception, employ line-commutated AC/DC converters in their front-ends, and fall into that category. Although these line-commutated, phase-controlled AC/DC converters are capable of handling giga-watt power levels, line-frequency commutation causes the currents they draw on the AC-side to be distorted, even though still to be periodic. These non-sinusoidal currents, drawn from the source, along the transmission lines and through other distribution system immittances, also give rise to non-sinusoidal voltage drops between the source and the load, which results in distorted voltage waveforms at other nodes and at the load. Harmonic penetration studies are essential to evaluate the performance of transmission systems in the presence of current distortion sources. These sources do not only bring about voltage distortion within the confines of their own borders, but extend their influence outside into those of other consumers as well. Supplyutilities are wary of the distortion introduced into their networks by consumers and initial recommendations have now given way to rigid standards for curbing harmonic pollution by consumers Because conventional steady-state alternating current circuit theory fails in the presence of distortion there are only two ways in which harmonic penetration studies can be carried out. Numerical integration methods are mandatory in the study of transient performance of electrical networks during switching and similar occurrences, but become cumbersome when the networks contain more than just a few nodes and are impossible to use when several tens or hundreds of nodes are encountered. Fortunately, harmonic penetration studies can be confined to steady-state operating conditions in a network in which voltages and currents are distorted but remain periodic and are therefore Fourier transformable. When viewed in the frequency-domain, non-sinusoidal but periodic current and voltage waveforms can be represented by discrete frequency spectra. Frequency-domain analysis offers a number of advantages. From the frequency-domain point of view, distortion can be quantified in terms of complex phasor values of voltages and currents at discrete harmonic frequencies that individually lend themselves to conventional circuit theory, permitting calculations to be carried out in extensive networks. Solutions that apply to these individual harmonic frequencies can then be summated across the spectrum to furnish aggregate or joint parameters of currents, voltages and powers and can also be transformed back into the time-domain for the reconstruction of the relevant time-dependent waveforms. Both the frequency and time-domain waveforms, of voltage and current, constructed in the above manner are concise and convey the same numerical information. When attempting, however, to quantify the circuit behaviour in terms of the classical definitions of active, reactive and apparent power, it is soon discovered that different definitions are possible. The different definitions, unfortunately, lead to divergent results and it is impossible to assess the utility of each different theory on a general basis. Only by applying the different theories in dedicated measurements, can their relative worth be established in terms of specific circumstances. That is the main theme of this dissertation.
36

Static and cyclic mechanical behaviour of helically-wound subsea power cables

Feld, Graham January 1992 (has links)
No description available.
37

A comprehensive approach to transmission pricing and its applications

Wei, Ping, 魏萍 January 2002 (has links)
published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy
38

Models of restructured electricity systems

Daxhelet, Olivier 09 May 2008 (has links)
The work presented in this thesis is a collection of four different research projects, conducted at the intersection between academic and industrial fields, and related to the restructuring of the electricity industry. Many models have been proposed to organise restructured electricity systems. We first propose a unified mathematical framework for expressing them, using variational inequalities. This allows the use of existence and uniqueness theorems, but also leads to models that can be solved by existing numerical algorithms. In the second part, we present a model of the European Commission proposals on cross-border trade, in particular access to the network and congestion issues. The model allows for various domestic regulation of the national non-eligible market, and different forms of competition in the eligible market. We illustrate this flexibility on a stylised example, and identify policy issues to be studied in a more realistic case study. The third contribution elaborates on the modelling of imperfect competition on electricity markets, more specifically the integration of imperfect competition behaviours in power models, through conjectural variations. We propose a consistent estimation procedure. Finally, a model of the EU Emission Trading Scheme, limiting the total CO2 emissions, is proposed. We illustrate the effect of some basic economic assumptions on the investment and generation mix, and how these assumptions impact the permit price and affect profitability. The novel part is in the way allocation mechanisms for subsequent commitment periods can potentially distort the behaviour of CO2 emitting agents.
39

Distance protection based on travelling waves

Crossley, P. A. January 1983 (has links)
No description available.
40

Algorithms for on-line measurement of harmonic damping and avoidance of harmonic resonances due to power factor capacitor switching in distribution systems

Bridgeman, M. January 2003 (has links)
No description available.

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