Development and test of resistive superconducting fault current limiter; acting time and its recovery conditions

Resistive-type of superconducting fault current limiters (RSFCL) have been developed for medium voltage class aiming to operate at 1 MVA power capacity and short time recovery (< 2 s). A RSFCL in form of superconducting modular device was designed and constructed using 50 m-length of YBCO coated conductor tapes for operation under 1 kV / 1 kA and acting time of 0.1 s. In order to increase the acting time the RSFCL was combined with an air-core reactor in parallel to increase the fault limiting time up to 1 s. The tests determined the electrical and thermal characteristics of the combined resistive/ inductive protection unit. The combined fault current limiter reached a limiting current of 583 A, corresponding to a limiting factor of 3.3 times within an acting time of up to 1 s

Analysis and Methodology for Determining the Parasitic Capacitances in VSI-fed IM Drives Based on PWM Technique

Three-phase induction motors present stray capacitances. The aim of this chapter is to present a methodology to experimentally determine these capacitances and also evaluate the effects of electromagnetic interference on motors in common mode. The proposed procedures for this methodology consist of: a) identifying the motor equivalent electrical circuit parameters through characteristic tests performed in the laboratory; b) setting up configurations between the PWM inverter and the motor for voltage and current measurements: common mode and shaft voltages, leakage and shaft (bearing) currents by using a dedicated measuring circuit; c) calculating the parasitic capacitance values between stator and frame, stator and rotor, rotor and frame and bearings of the motor using the capacitance characteristic equation; d) using the dedicated software Pspice to simulate the system composed by the three-phase induction motor fed by PWM inverter with the equivalent electrical circuit parameters; e) determining the characteristic waveforms involved in the common mode phenomenon

The effect of superplasticizers on the workability and compressive strength of concrete made with fine recycled concrete aggregates

The reuse of structural concrete elements to produce new concrete aggregates is accepted as an alternative to dumping them and is favourable to the sustainability of natural reserves. Even though the construction sector is familiar with the use of coarse recycled concrete aggregates, the recycled concrete fines are classified as less noble resources. This research sets out to limit the disadvantages associated with the performance of concrete containing fine recycled concrete aggregates through the use of superplasticisers. Two types of latest generation superplasticisers were used that differ in terms of water reduction capacity and robustness, and the workability, density and compressive strength of each of the compositions analysed were then compared: a reference concrete, with no plasticisers, and concrete mixes with the superplasticisers. For each concrete family mixes with 0%, 10%, 30%, 50% and 100% replacement ratios of fine natural aggregates (FNA) by fine recycled concrete aggregates (FRA) were analysed. Concrete with incorporation of recycled aggregates was found to have poorer relative performance. The mechanical performance of concrete with recycled aggregates and superplasticisers was generally superior to that of the reference concrete with no admixtures and of conventional concrete with lower performance superplasticisers

Avaliação das consequências de galgamento sobre estruturas portuárias: caso de estudo da praia da Vitória, Açores

Dissertação para obtenção do grau de Mestre em Engenharia Civil na Área de Especialização em HidráulicaA presente dissertação, inserida na área de especialização de hidráulica de engenharia civil, procura avaliar o risco de galgamento sobre estruturas portuárias. Devido à ocorrência de galgamentos, há necessidade em garantir a segurança de bens, pessoas, equipamentos, estruturas e atividades junto a elas desenvolvidas e, ainda, em precaver gastos a nível económico. Nesse sentido, recorre-se neste trabalho a previsões da agitação marítima em águas profundas fornecidas pelo modelo WAM que, acoplado aos modelos SWAN e DREAMS, permite a caracterização do estado de agitação do mar junto à estrutura portuária. Posteriormente, aplica-se a ferramenta neuronal NN_OVERTOPPING2 que fornece os caudais médios galgados nas estruturas. Seguidamente, recorre-se a três metodologias distintas para avaliar as consequências do galgamento: uma metodologia simples, Analytic Hierarchy Process (AHP) e Analytic Network Process (ANP). As metodologias multicritério AHP e ANP tornam-se mais vantajosas em relação à metodologia simples, na medida em que permitem análises espaciais definindo o risco a que cada área está sujeita. Estas melhorias sustentam uma avaliação do risco mais fiável, o que é fundamental para o apoio à tomada de decisão e numa gestão eficaz das zonas costeiras e portuárias. Por fim, aplica-se o procedimento descrito ao porto da Praia da Vitória (Açores, Portugal).Abstract: This dissertation, developed within the hydraulics branch of civil engineering, aims at contributing to the assessment of the risk associated to the wave overtopping of port structures. Due to the occurrence of overtopping, there is a requirement to ensure the safety of goods, people, equipment, structures and activities developed in their surroundings and, still, avoid economic spending. Therefore, the study uses forecast wave conditions in deep water, provided by the WAMmodel, which coupled to SWAN and DREAMS models, allows to characterize the sea state near the port structure. Subsequently, the NN_OVERTOPPING2 artificial neuronal tool is applied, which provides the mean flow overtopping discharge over the structures. Finally, three different methodologies to assess the consequences of wave overtopping are used: a simple methodology, the Analytic Hierarchy Process (AHP) and the Analytic Network Process (ANP). The multi-criteria AHP and ANP methodologies are more advantageous in comparison with the simplistic methodology, since they allow spatial analysis and definition of the risk that each area is subject to. These improvements support a more reliable risk assessment, which is essential in the decision-making process and in a effective management of coastal and port areas. The procedure in this study is applied in the port of Praia da Vitória (Azores, Portugal).N/