Incipient turn-to-turn winding fault diagnosis of power transformers by the on-load exciting current Extended Park`s Vector Approach

This paper presents the application of the on-load exciting current Extended Park's Vector Approach for diagnosing incipient turn-to-turn winding faults in operating power transformers. Experimental and simulated test results demonstrate the effectiveness of the proposed technique, which is based on the spectral analysis of the AC component of the on-load exciting current Park's Vector modulus.

Transformers on-load exciting current Park`s vector approach as a tool for winding faults diagnostics

This paper presents the development of a new approach for diagnosing the occurrence of inter-turn short-circuits in the windings of three-phase transformers, which is based on the on-line monitoring of the on-load exciting current Park's Vector patterns. Experimental and simulated results demonstrate the effectiveness of the proposed technique for detecting winding inter-turn insulation faults in operating three-phase transformers.

Condition monitoring and diagnostics of power transformers

This paper addresses the subject of condition monitoring and diagnostics of power transformers. The main results of two reliability surveys, carried out under the auspices of CIGRE and IEEE in order to assemble objective data on the performance of transformers in service, are presented, providing useful information on the main causes of transformer failures, the most likely affected components and the related outages times. A survey of the most important methods, actually in use, for condition monitoring and diagnostics of power transformers is also given, which stresses the need for the development of new diagnostic methods, that can be applied without taking the transformers out of service, and that can also provide a fault severity criteria, in particular for determining transformers windings integrity. Preliminary results, concerning the on-going research activity on the development of a new approach for inter-turn winding fault diagnosis in three-phase transformers, are also reported in the paper.

Modelling and simulation of three-phase power transformers

This paper presents the development and implementation of a digital simulation model of a three-phase, three-leg, power transformer. The proposed model, implemented in MATLAB environment, is based on the physical concept of representing windings as mutually coupled coils, and it is intended to study its adequacy to incorporate, at a later stage, the influences of the occurrence of windings inter- turn short-circuits. Both simulation and laboratory tests results, obtained so far, for a three-phase, 6 kVA transformer, demonstrate the adequacy of the model under normal operating conditions.

Condition monitoring and diagnostics of power transformers

This paper addresses the subject of condition monitoring and diagnostics of power transformers. The main results of two reliability surveys, carried out under the auspices of CIGRE and IEEE in order to assemble objective data on the performance of transformers in service, are presented, providing useful information on the main causes of transformer failures, the most likely affected components and the related outages times. A survey of the most important methods, actually in use, for condition monitoring and diagnostics of power transformers is also given, which stresses the need for the development of new diagnostic methods, that can be applied without taking the transformers out of service, and that can also provide a fault severity criteria, in particular for determining transformers windings integrity. Preliminary results, concerning the on-going research activity on the development of a new approach for inter-turn winding fault diagnosis in three-phase transformers, are also reported in the paper.

Produção de "single cell oil" por Yarrowia lipolytica : seleção de meios de cultura

Com o crescimento económico e populacional, as necessidades energéticas globais aumentam diariamente. Juntamente com a percepção de que os combustíveis fósseis são finitos e com uma progressiva consciência ambiental, os biocombustíveis são vistos como a alternativa a seguir. A produção de biodiesel a partir da transesterificação de óleos vegetais aumenta a deflorestação e o custo de bens alimentares. Como alternativa, surgem os óleos de origem microbiana – single cell oil (SCO) - acumulados principalmente como triacilgliceróis, a mesma forma dos óleos vegetais, podendo ser utilizados para biodiesel ou como lípidos de alto valor acrescentado. Contudo, a utilização de microrganismos para síntese de lípidos está limitada pelos custos associados ao processo de produção. Este bioprocesso torna-se economicamente mais favorável quando resíduos obtidos a baixo custo são utilizados como fonte de carbono. Assim, o objectivo deste trabalho foi estudar a possibilidade de utilização de subprodutos de diversas indústrias (glicerol bruto e banha de porco) e glicerol puro na produção de SCO, utilizando a levedura Yarrowia lipolytica. Foram realizados ensaios em batch em matraz de 500 mL, matraz de 1000 mL e biorreator de 2 L, de modo a estudar qual o melhor substrato e concentração para produção de SCO. Verificou-se que a banha é o substrato mais eficaz para a acumulação de gordura pela estirpe Y. lipolytica W29, seguida do glicerol bruto, enquanto o glicerol puro mostrou ser a fonte de carbono menos adequada. Encontrou-se um intervalo de concentração de glicerol bruto para produção de SCO, enquanto que a concentração de banha no meio não afeta a acumulação de gordura pelas células. Os ácidos gordos preferencialmente acumulados pelas células em meio com banha e glicerol bruto foram o ácido oleico e o linoleico, respetivamente. Nos meios com glicerol puro e bruto observou-se a produção de ácido cítrico, o que não se verificou em meio com banha.

Development of an operational tool for oil spill forecast: application to oil exposed regions

Tese de doutoramento, Ciências do Mar, da Terra e do Ambiente (Modelação), Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2014