197,745 research outputs found
Estudo da interferência eletromagnética gerada por redes PLC (power line communication) no interior de edificações
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.Os níveis de Interferência Eletromagnética (EMI) gerada por uma rede PLC, devido ao número limitado de testes já efetuados, ainda são pouco conhecidos no Brasil. Basicamente, o tema pode ser dividido em duas partes: A interferência provocada pela rede PLC em outros sistemas que compartilham o mesmo ambiente operacional e aquela provocada por outros sistemas licenciados causando distúrbios na operação de um sistema PLC. O primeiro caso se relaciona diretamente ao nível dos sinais interferentes que o organismo de regulação determinará como limite para operação dos sistemas PLC e o segundo caso se refere à redução do espectro disponível para a PLC causado pela interferência gerada por outros sistemas, implicando em taxas de transmissão muito baixas, e inviabilizando assim sua implantação. Considerando o provável público-alvo dessa aplicação, a implantação da PLC se viabilizará em locais de grande concentração urbana onde já existem outros sistemas operando na mesma faixa de frequência. Portanto, o prévio conhecimento do comportamento de uma rede PLC se revela de extrema importância para o sucesso da tecnologia. Diante disto, o objetivo principal deste trabalho é fornecer subsídios técnicos que comprovem a aplicabilidade da PLC em áreas internas a edificações, também conhecida como aplicações indoor da tecnologia Power Line Communication
Psychosocial interventions and opioid detoxification for drug misuse: summary of NICE guidance
No full textDrug misuse is an increasing problem that not only impairs the physical and mental health of people who misuse drugs but also negatively affects their families and wider society (for example, in its association with crime). Recently expanded drug services in the United Kingdom involve general practitioners to a considerable degree, who care for at least a third of opioid misusers in treatment. Many clinicians remain pessimistic, however, about the possible benefits of any treatment and how to engage drug users in treatment.1 This article summarises two new NICE guidelines that identify the most effective, safe detoxification regimens for primary and secondary care, the most cost effective psychosocial interventions, and effective ways to promote patient engagement
Improved damper cage design for salient-pole synchronous generators
No full textThe benefits of implementing a damper winding in salient-pole, synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field, synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such ’classical’ machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4MVA, salient-pole, synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimised machine is compared to the original design both at steady state and transient operating conditions
Global design optimization strategy of a synchronous reluctance machine for light electric vehicles
No full textSynchronous Reluctance (SynRel) machines are considered a competitive alternative to the induction motors for variable speed drive applications due to their comparable performances and low cost. The absence of rare earth permanent magnets makes them very attractive also in the automotive sector especially for light electric vehicles. The design of SynRel machines has been formalized by many authors in the last three decades but it is still an open challenge since it involves many competitive design objectives and a higher number of geometrical variables compared to other kind of machines. This paper is focused on the joint optimization of both stator and rotor of a SynRel machine with the aim of obtaining the highest torque density with the minimum iron and joule losses as well as smooth torque. The aim is to carry out a machine design that suits best the requirements of a small electric car for urban mobility, i.e. 30 kW with a base speed of 3000 rpm and a maximum speed of 6000 rpm. The proposed optimization strategy is global because it considers a geometry design that takes into account several stator and rotor parameters together. The design method consists in a two steps procedure: in the first stage the torque density and the losses are optimized, while the quality of the torque profile is improved in the second design stage. The results, satisfying the project requirements, are presented and compared to the initial reference machine. Finally a comparison between two design approaches allowing the improvements of the constant power speed range is presented and discussed
Damper cage loss reduction and no-load voltage THD improvements in salient-pole synchronous generators
No full textSalient-pole synchronous generators (SG) have a long history of utilization as reliable power generation systems. Important aspects of such generators include a high power-to-weight ratio, high efficiency and a low cost per kVA output [1]. Another critical aspect is the requirement for very low harmonic content in the output voltage. Hence, it is very important to be able to model and predict the no-load voltage waveform in an accurate manner in order to be able to satisfy standards requirements, such as the permissible total harmonic distortion (THD). Also, at steady-state conditions, parasitic voltages are induced in the damper bars which lead to a current flow with associated power losses and an increase in temperatures. This paper deals with an in-detail analysis of a 4 MVA SG, whose operation is studied and compared with experimental results for validation purposes. The same platform is then used to propose innovative solutions to the existing design and operational challenges of the machine aimed at reducing ohmic loss in the damper cage and improving the output voltage THD, without reverting to disruptive techniques such as rotor and/or stator skewing
End barrier shape optimizations and sensitivity analysis of synchrnous reluctance machines
No full textThis paper presents an extensive study on the electromagnetic and structural influences of the end barrier shape of a Synchronous Reluctance Machine (SynRel). One of the most challenging tasks in designing these machines is to achieve a smooth torque and a mechanically robust structure, especially when high operating speed range is required. Several papers have already addressed the electromagnetic design problem related to the choice of the flux barriers thicknesses and positions. However a comprehensive work on the influence of the end part of the flux barrier on the electromagnetic and structural performance has not been yet presented. In this work two end barrier shapes are considered and optimized using the same methodology. Then the optimized machines have been deeply analyzed in terms of torque, torque ripple and rotor von Mises stress distribution. Furthermore, with the aim to further investigate the influence of such end barrier shape, a detailed sensitivity analysis is presented. In conclusion, general guidelines for the structural and electromagnetic design of such end barrier shape are drawn
End barrier shape optimizations and sensitivity analysis of synchrnous reluctance machines
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Hairpin windings: Sensitivity analysis and guidelines to reduce ac losses
No full textNowadays, electrification in the transportation sector is one of the most viable solutions to reduce CO2 emissions and meet fuel economy requirements. Being the electrical machine one of the most important players in this electrification trend, extensive research is currently being dedicated to the improvement of their efficiency and power density. In automotive applications, hairpin technologies are widely spreading due to their potential in reducing costs and life cycles in a mass production perspective, as well as in increasing the torque capabilities of machines. However, several challenges need to be addressed before the complete replacement of random windings with hairpins can take place. Of these challenges, the loss produced during high frequency operations is one of the most limiting. This paper aims at studying and investigating high frequency (AC) losses for different slot geometries and conductor cross sections, which in turn involve the analysis of different slots-per-pole-per-phase / layers-per-slot combinations. In addition, the effects on the AC losses of reducing the slot fill factor are studied, either by removing the closest conductors to the slot opening or by reducing the hairpin legs' height. Analytical and numerical models are employed to investigate these concepts
High speed drives review: Machines, converters and applications
No full textThe development of new power electronic device and high performance magnetic materials are the main technological factors that have led both industries and research community to focus their attention on high speed electrical drives. Several papers have already outlined the electrical machine and/or converter topology choice for certain high speed application. This choice obviously depends on the applications under study. This paper aims to identify the most important high speed applications. For each of them, the main design challenges are highlighted and an overview of the already available product on the market is presented
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