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- Eco-Friendly Ester Fluid for Power Transformers versus Mineral Oil: Design ConsiderationsPublication . Nogueira, Teresa; Beleza Carvalho, José António; Magano, JoséMineral oil has long been used as an adequate coolant and dielectric medium in power transformer design. However, it is flammable and environmentally risky as it may be leaked or spilled. Therefore, ester fluids, which have been increasingly used in the last two decades, look promising as an ideal dielectric option. This research aims to better understand how using ester fluid insulation in power transformers impacts their physical and electrical dimensions, including their load-losses, impedance, masses, and equipment dimensions. Three case studies were carried out in a Portuguese electrical equipment manufacturer’s facility, with varying electrical parameters and physical properties of the mineral oil and ester-filled power transformers. The main results enhanced the known good electrical behavior of ester fluids, namely creating a lower electric field around winding wedges, yet the use of ester fluids led to higher load-losses, larger masses, additional radiators and, consequently, higher manufacturing costs. Nevertheless, the contribution of ester-filled power transformers to the improved environmental safety (reducing spillage and fire risks), among other advantages, makes ester fluids a truly eco-friendly option for power transformer design.
- Sistemas híbridos de armazenamento e produção de energiaPublication . Gonçalves, Rodrigo Leitão Monteiro; Carvalho, José António Beleza; Gonçalves, Manuel João DiasO presente documento tem como objetivo o estudo das características técnicas e económicas de sistemas de armazenamento de energia e as possibilidades, vantagens e condicionantes da sua integração em centrais de produção de energia intermitente. Numa fase posterior será apresentado o caso de estudo composto por três partes, sendo a primeira uma avaliação técnica da reconversão da central termoelétrica, respeitando o projeto proposto pela Endesa; seguindo-se uma análise do comportamento distinto do sistema de armazenamento de energia elétrica e da produção de hidrogénio, durante 3 meses de inverno e 3 meses de verão.
- EditorialPublication . Carvalho, José António Beleza; Beleza Carvalho, José António(Excerto editorial) Voltamos à vossa presença com mais uma publicação da nossa revista “Neutro-à-Terra”. Ao fim de 16 anos continuamos a intervir, semestralmente, na área científica da Engenharia Eletrotécnica, com a publicação de vários artigos técnicos e científicos que procuram ser uma mais valia na resolução de problemas nesta vertente da Engenharia, mas também uma forma de apoio aos estudantes e a todos os profissionais de Engenharia Eletrotécnica.
- Physiopathological effects of electric current on the human body and the protection against electric shocksPublication . Carvalho, José António Beleza; Beleza Carvalho, José António; Almeida, Maria; Silva, Catarina; Costa, CarolinaIn electrical installations and equipment, electric current preferentially flows through metallic circuits that offer it less opposition, that is, less electrical resistance. In the human body, electric current also seeks to flow through paths with less electrical resistance, and may be diverted inside the body, damaging surrounding organs and tissues. Its path and the magnitude of the current influence the type of injuries associated with electrical accidents, usually burns, which can be internal and external. In all electrical installations, there is a need and obligation to implement effective protection systems, with the aim of operating them under safe conditions. In Low Voltage Electrical Installations (LVEI), the protection measures that must be considered are overcurrent protection, overvoltage protection, but fundamentally the protection of people from the risk of electrocution, avoiding pathophysiological effects that can be irreversible.
- Safety in the operation of electrical networks: Inertia compensation as a measure of frequency and voltage stabilityPublication . Carvalho, José; Beleza Carvalho, José AntónioThe main purpose of electrical transmission and distribution networks is to carry electrical energy from the places where it is produced to the places of consumption, where the energy is used. Electrical energy is produced in power plants by generating units, which convert a form of primary energy into electrical energy. Primary energy comes from a number of sources, such as fossil fuels, nuclear energy, hydropower, wind, and solar. The carbon neutrality targets set by the European Union and several countries around the world have driven a transformation characterized by the gradual replacement of synchronous thermal generation based on fossil fuels with Renewable Energy Sources (RES), such as wind and solar. The energy transition, while necessary to achieve the established targets, introduces significant challenges to the stability of Electrical Power Systems (EPS) and electrical grids, since RES do not yet contribute to stability at levels comparable to the generating units of large thermal power plants, whether in terms of inertia, which has seen a notable reduction in recent years, or in voltage control or short-circuit power. This article presents and discusses solutions to mitigate the effect of this reduction in inertia in power plants using synchronous compensators and synthetic inertia emulation using battery storage.