Intrabuilding power distribution circuits offer a number of unique advantages for local area networking. To enable the selection of proper error-control codes and protocols for reliable data communication services, error pattern statistics of intrabuilding power line channels are obtained. Also, error-causing disturbances are identified and their relationships to specific types of error patterns are determined. It is found that error occurrence is highly periodic, with periodicity being a function of the power line frequency which is nominally 60Hz in North America. Furthermore, results indicate that error pattern behaviour is relatively insensitive to communication carrier frequency and modulation schemes. Based on the measurement results, hybrid ARQ with bit-interleaving is suggested for reliable data transmission at high data rate (19,200bps). Burst error correcting codes can be used to reduce decoder cost and complexity with some sacrifices in performance. At lower data rates (1,200bps or below), effective error control can be accomplished more easily. Finally, the attenuation characteristics of a number of typical power line channels are presented. It is found that high frequency bypass can be used to improve signal transmission between different phases of the distribution transformer. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

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.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

<p>The rapid development of wind power technology is reshaping conventional power grids in many countries across the world. As the installed capacity of wind power increases, its impact on power grids is becoming more important. To ensure the reliable operation of a power system which is significantly fed by wind power, the dynamics of the power system must be understood, and the purpose of this study is to develop suitable analytical tools for analysing the dynamic impact of large-scale wind parks on the stability of a power grid, and to investigate the possibility of improving the stabilisation and damping of the grid by smart control strategies for wind turbines.Many of the newer, larger turbines now being produced are variable speed turbines, which use doubly fed induction generators (DFIGs). These are induction generators which have their stator and rotor independently excited. When unconventional generators of this type are used in a power system, the system behaves differently under abnormal dynamic events.  For example, new types of generators cause different modes of oscillation in the power system, not only because of their dynamic characteristics, but also because they load the system differently.Very large power oscillations can occur in a power system as a result of internal disturbances.  Ordinarily these oscillations are slow and, in principle, it is possible to damp them with the help of wind power.  This leads to the idea of using a power system stabiliser (PSS) for a DFIG.  In order to damp oscillations in the system, it is necessary to understand the equipment causing these oscillations, and the methods to optimally damp the oscillations.Voltage stability is another important aspect of the safe operation of a power system. It has been shown that the voltage stability of a power system is affected by induction generators.  The voltage stability must therefore be carefully analysed in order to guard against a power system collapse.By using modal analysis and dynamic simulations, we show that the presence of a wind farm in the vicinity of a power system will improve the angular behaviour of the power system under small disturbances, but may decrease voltage stability under larger disturbances. We compare the performance of wind turbines to that of conventional synchronous generator power plants, and we show that a wind park consisting of DFIGs, which are equipped with PSSs, may be used as a positive contribution to power system damping.</p>

No description available.

<p>The rapid development of the global economics has made power systems allover the world become large-scale interconnected grids. This increases the capabilityof power grids to transfer power over the long distance to serve the desiredpower demand with the minimum cost of operation. Unfortunately, it alsoenables the propagation of local failures into global networks. In other words,if a blackout happens in a power system, the size and the damage may significantlyincrease.</p><p>One of the main ways in which blackouts become widespread is cascadingfailures. This type of failure originates after a critical component of the systemhas been removed fromthe service by protective relaying. As a consequence, theload handled by the failed component needs to be redistributed which mightcause an overloading on other components in the system.</p><p>On the other hand, the high power electronics controllable devices suchas Voltage Source Converters-based High Voltage Direct Current (VSC-HVDC)transmission are recently developed. These electronics devices have the potentialadvantages such as the ability to independently control active and reactivepower, and maintain voltage to be at acceptable level. Therefore, they are consideredto be the promising devices that with an appropriately designed controlstrategy, they can substantially improve the performance and reliability of thepower system.</p><p>This thesis presents the possibility to consider protection system status inthe control of VSC-HVDC link. A great deal of this research is development ofcoordination between this power electronic device and protection system which normally are considered separately. The derivation of protection system has been selected to determine the operation of VSC-HVDC. The methodology isbased on utilizing the signal created from a logical evaluation of relay and simplificationsof certain parameters. By introducing information from the relays tothe VSC-HVDC link via Central Control Unit (CCU), the modulation of transmitted power is devised in order to reduce the risk of system-wide failures. In turn,this means an avoided blackout.Furthermore, this thesis also includes the preliminary suggestion to selectthe location of VSC-HVDC. The methodology is based on predicting voltage instabilityusing voltage stability indices and related parameterswhich are derivedby using Singular ValueDecomposition method. The solutions indicate an effectivelocation for applying corrective action such as load shedding. This optimallocation is selected to reinforce the control strategy of VSC-HVDC in order toprevent cascading failures in the more encompassing systems.</p> / QC20100615

M.Ing. / Currently, electrical resistance heaters are used to produce most of the hot water in South Africa. Increasing electricity tariffs make these devices very expensive. This study investigates the economic savings potential of using a cogeneration system made of microturbines, heat pumps and heat exchangers. Specifically the heating of water for large residential units is investigated. Different economic parameters are used to compare microturbine heat pump systems with electrical resistance heaters, natural gas boilers and heat pumps. For 27 main centres in South Africa, the amount of hot water is determined where a cogeneration system is economically more viable than other types of water heaters. It has been concluded that the most important influence factor is the electricity tariff. The higher the electricity tariff in a city, the smaller the number of domestic consumers where a cogeneration system becomes viable.

O objetivo central desta dissertação é o desenvolvimento de uma metodologia para a avaliação de alternativas de oferta e gerenciamento de demanda de energia em Honduras. O estudo enfatiza o setor residencial da ZMVS (Zona Metropolitana Del Valle de Sula), no norte de Honduras, identificada como a região de maior potencial de eficiência energética no país. A caracterização dos usos finais da energia e as curvas de carga, foram realizadas a partir da pesquisa de campo desenvolvida na ZMVS pela ENEE (Empresa Nacional de Energia Elétrica) e a OLADE. Os programas de eficiência energética analisados compreendem a substituição de lâmpadas incandescentes de 50, 60W pelas fluorescentes compactas de 20 W, a troca, após o término de sua vida útil, de fogões elétricos por fogões a GLP; a troca após o término de sua vida útil, de geladeiras de alto consumo por geladeiras eficientes e a troca de condicionadores de ar de alto consumo por condicionadores de ar mais eficientes. Na avaliação da efetividade econômico-financeira desses programas foram consideradas três diferentes perspectivas: do consumo, das concessionárias e da sociedade. Os resultados indicam a viabilidade de programas de eficiência energética e de gerenciamento da demanda, já que têm custos menores aos de suprimento. / The main objective of this work is the development of a methodology for the integrated analysis of energy demand side and supply alternatives in Honduras. This work emphasizes the residential sector of the ZMVS (Sula Valley Metropolitan Area), in the Honduran north coast, identified as having the most promising energy efficiency potential region in the country. Energy end uses and load curve characterization was carried out by ENEE and OLADE investigation developed for the ZMVS region. Energy demand side management programs evaluated comprise: substitution of 20W compact fluorescent lamps for 50 and 60 W incandescent bulbs; substitution of LPG stoves for electric stoves, after their useful life; substitution of efficient for inefficient refrigerators; and replacement of air conditioning equipment with ERR at 8,8 or less with more efficient airs conditioning equipment. Economic evaluation of the programs was carried out under three different perspectives: the consumer, the utility and the perspective of society. Results indicate that energy efficiency and energy demand side management programs are cost-effective, since their costs are lower than equivalent supply-side options.

Esta dissertação analisa a situação atual e as perspectivas de melhoramento da eficiência energética no cultivo de flores da região norte do Equador. Foi realizada uma pesquisa de campo, caracterizando o use da energia elétrica para esse subsetor. Os usos finais identificados foram: irrigação, iluminação, sublimadores, câmaras de refrigeração e serviços gerais. Além das características elétricas foram pesquisados dados sócio-econômicos, com a finalidade de avaliar de forma global a participação das agroindústrias na região. Os resultados deste estudo mostram a grande conveniência de se utilizar tecnologias mais eficientes na iluminação devotada para o cultivo de flores. Também são apresentadas recomendações na operação dos sistemas de irrigação e câmaras de refrigeração. As medidas de racionalização sugeridas neste trabalho visam o benefício econômico não apenas das agroindústrias mas também da concessionária e da sociedade. / This report analises the present situation and the improvement perspectives of energy efficiency in the flower culture in Northern Region of Equador. A field research was carried out in order to charaterize the use of electric power by this subsetor. The end use identified were: irrigation, lighting, sublimation, refrigeration (chambers) and general services. Socio-economic data were researched, beyond the eletrical charateristics, to evaluate the global share of the agro-industries in the region. The results of this study show the great convenience of using more efficient technologies in the lighting of flower cultures and also presents recomendation to the operation of the irrigation and refrigeration (chambers) systems. The racionalization measures sugested in this work view not only the economic benefit of the agro industrives but also of the society and the utility.