Hydraulic assessment of nanofluids based on mineral oil and natural ester in windings of power transformers

It is common for electric power transformers to be cooled by mineral oil. However, this type of oil has begun to be replaced by oils of natural origin (esters), due to environmental and fire safety reasons. The latter are biodegradable and have an ignition point much higher than that of mineral oils. On the other hand, different authors have found that the dielectric and refrigerant properties of the oils used in transformers can be improved when some types of nanoparticles are added. In order to assess this improvement, this work presents the results obtained by a research in which different nanofluids, produced through commercial dielectric oils (mineral and natural), nanoparticles of titanium (IV) oxide and magnetite, were thermally characterized. The results of this characterization have been used to perform simulations based on computational fluid dynamics. This comparison has allowed to observe the pressure drops and the mass flows in the internal channels of the windings of a real power transformer.The authors of this research wish to thank the Ministry of Economy for financial support to the National Research Project: Improvement of Insulation Systems of Transformers through Dielectric Nanofluids (DPI2015-71219-C2 1-R)

Dielectric and mechanical assessment of cellulosic insulation during transformer manufacturing

Due to the impact of cellulose of paper insulation on transformer life, it is imperatire to remove moisture from the oil and the solid insulation. Several techniques have been implemented during manufacturing of power transformers to reduce water content in transformers. These drying processes can involve different costs and time, and they can damage the insulation paper. In this work, a drying process has been implemented in the laboratory trying to simulate the most aggressive conditions that can be suffered by the paper in transformer manufacturing in a real industry. Once the moisture content of papers was lower than 0.5%, the effect of the drying process on paper degradation was evaluated using the analysis of mechanical and dielectric properties and the degree of polymerization. Different commercial papers were studied to quantify the possible degradation induced by the drying process. The results of the mechanical strength study showed a reduction on the degree of polymerization from 1100 to 850 after 4 days of drying. The dielectric analysis of the samples showed different behavior in one of the solids evaluated and it was also found a decreased hygroscopic capacity of degraded samples in comparison with new samples.This research is under the National Research Project “Gestión del Ciclo de Vida de Transformadores Aislados con Fluidos Biodegradables” (PID2019-107126RB-C22/ AEI /10.13039/501100011033). The authors also wish to thank “Fundación Iberdrola” for its financial support for the research project: “Análisis de las Propiedades Dieléctricas de Aislamientos Sólidos Impregnados con Líquidos Dieléctricos”. C. Méndez would like to acknowledge the Spanish Ministry of Science, Innovation and Universities for the financial support for the FPU grant (FPU19/01849)

Study of the impregnation of power-transformer cellulosic materials with dielectric ester oils

The application of alternative dielectric oils as esters in power transformers is hindered by the lack of knowledge regarding their properties and respecting which are the best techniques to ensure their proper performance. In this sense one of the fields needing an impulse is the impregnation processes of transformers cellulosic materials with these alternative oils, currently impregnated in most of the cases with mineral oils. This paper studies the impregnation behavior of eight usual dielectric solids, with two esters and a traditional mineral oil. Empirical equations of the impregnation evolution with time have been obtained, from these the rigid cellulosic materials present in the transformers and the viscosity of the dielectric oils have been identified as the key materials and properties to consider during impregnation. An adaptation of the current impregnation processes to the alternative oils have been proposed by increasing their temperature from ambient temperature up to 61-74°C, depending on the viscosity of the oil used.This work was supported in part by the Spanish Ministry of Science and Innovation by the National Research Project Asset Management of Biodegradable-Fluid-Based Transformers under Grant PID2019-107126RB-C22/AEI/ 10.13039/501100011033, in part by the Universities and Research Council of the Government of Cantabria by the Grant ‘‘Biodegradable Fluids in Electrical Power Transformers: Solid Dielectric Impregnation and Thermal Modeling with Thermal Hydraulic Network Models (THNM)’’ under Grant VP32, 2019-2, and in part by the University of Cantabria through the Industrial Doctoral Program 2016, Scholarship DI13

Impregnation processes of insulation rigid components of cellulose in synthetic ester and mineral oil

Although oil-immersed power transformers generally use mineral oil as insulation and cooling fluid, this liquid does not meet the new technical requirements of dielectric fluids such as high biodegradability, non-toxicity and high safety. For these reasons, natural and synthetic esters as alternative to mineral oil have increased their utilization in some transformers installations. Despite the fact that there are several works that have demonstrated the suitability of these insulation fluids from the point of view of their stability, dielectric and thermal properties, there are very few works focused on the study of the effects of these liquids on impregnation process. The aim of this work is provide information about the behavior of different rigid insulation materials, not studied until now, during the impregnation process in a synthetic ester compared with a mineral oil.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 823969-BIOTRAF

Investigation of the degradation of a wood pulp-cotton presspaper in different biodegradable oils

New insulating materials, as biodegradable oils and upgraded paper, need to be investigated. In this paper, the ageing of a wood pulp - cotton presspaper is studied. Solid insulation is impregnated and aged with three different fluids: a mineral oil and two vegetable oils, from sunflower and soybean. Both oils and paper were dried before the ageing process, which was carried out at 150°C for 732 hours in iron vessels. Degradation of oils is analysed through the measurement of their breakdown voltage, dielectric dissipation factor (tan δ), resistivity, moisture content and acidity. Deterioration of presspaper is quantified by its polymerization degree (DP), moisture content and dielectric dissipation factor. Results showed that the dielectric properties of oils are negatively affected by the ageing, since the breakdown voltage and resistivity were reduced, whereas the dissipation factor increased. Also, acidity increased, especially in the vegetable oils. In the case of the solid insulation, its tanδ increased with the ageing, despite the reduction of its moisture content. DP was reduced, reaching the end-of-life criteria (DP<200) in the ageing with mineral oil (134) whereas it remained at higher values for the sunflower (206) and soybean (216) oils.This research is under BIOTRAFO project, which has received funding from the European Union’s Horizon 2020 Research and Innovation Program under the Marie Sklodowska-Curie Action-Research and Innovation Staff Exchange (MSCA-RISE) grant agreement No 823969. The authors of this research wish to thank the Ministry of Economy for its financial support for the National Research Project: Gestión del Ciclo de Vida de Transformadores Aislados con Fluidos Biodegradables (PID 2019-107126RBC22). Cristina Méndez also wants to acknowledge the Spanish Ministry of Science, Innovation and Universities for the financial support for the FPU grant (FPU19/01849)

Adaptation of the impregnation conditions of cellulosic transformer solids to the use of natural esters

Transformers’ operation and end of life mainly depend on its solid insulation. It is subjected to different stresses that cause the cellulose degradation. The ageing process is highly dependent on the moisture content and the correct impregnation. In the impregnation process, the dielectric coolant fluid is absorbed by the rest of the transformer porous materials, especially the insulating cellulosic materials, conditioning their properties. Due to the transition to a more sustainable energy system, new lines of research that explore alternatives to traditional mineral oils, as esters, are being developed. However, it is necessary to study their behaviour in the different manufacturing processes and during the operating life of the transformers for their future application. In this paper, the changes to be made in the impregnation process to include a soya-based liquid, taking the place of mineral oil, and considering as solid dielectrics Crepe Paper, Diamond Dotted Paper (DDP), Kraft and Presspaper (PSP) are studied.Work supported in part by the Spanish Ministry of Science and Innovation (National Research Project Asset Management of Biodegradable-Fluid-Based Transformers under Grant PID2019-107126RB-C22/AEI/ 10.13039/501100011033), by the Universities and Research Council of the Government of Cantabria (Project ‘‘Biodegradable Fluids in Electrical Power Transformers: Solid Dielectric Impregnation and Thermal Modeling with Thermal Hydraulic Network Models (THNM)’’ under Grant VP32, 2019-2), and by the University of Cantabria (Industrial Doctoral Program 2016, Scholarship DI13)

Desarrollo de un sistema interactivo para el estudio de la órbita y su contenido: anatomía microscópica

Se ha desarrollado un sistema interactivo para mejorar el proceso de enseñanza-aprendizaje en la docencia de la anatomía microscópica de la órbita y su contenido, a través de preparaciones histológicas. Se pretende facilitar el aprendizaje de forma autónoma en español e inglés y, la autoevaluación sobre los conocimientos adquiridos

Desarrollo de un sistema interactivo para el estudio de la órbita y su contenido: anatomía macroscópica

En este proyecto se ha desarrollado un sistema interactivo para mejorar el proceso de enseñanza-aprendizaje en la docencia de la anatomía macroscópica de la órbita y su contenido por medio de preparaciones anatómicas. Se pretende facilitar el aprendizaje de forma autónoma en español e inglés y, la autoevaluación sobre los conocimientos adquiridos.Unidad Docente de Anatomía y EmbriologíaFac. de Óptica y OptometríaFALSEsubmitte

Characterization of the impregnation with biodegradable oils of solid dielectric materials of power transformers

La electricidad es esencial en la sociedad actual, abarcando un 20% de la demanda energética mundial. Los transformadores eléctricos son vitales en el sistema eléctrico, ya que ajustan las tensiones para un transporte eficiente y la adaptación al usuario final. Estos equipos emplean materiales celulósicos como aislamiento, además de aceite mineral con un fin aislante y refrigerante. Este fluido presenta problemas técnicos y ambientales debido a su riesgo de incendio y baja biodegradabilidad. Para abordar estos problemas, se investigan como alternativas al aceite mineral fluidos dieléctricos biodegradables con altos puntos de inflamación. Sin embargo, enfrentan desafíos, como la impregnación de materiales dieléctricos sólidos, proceso crítico en la fabricación de transformadores. Este trabajo busca mejorar la transición hacia fluidos biodegradables analizando soluciones para aumentar la velocidad de la impregnación, como el aumento de temperatura.Electricity is essential in today's society, covering 20% of global energy demand. Electrical transformers are vital in the electrical system, as they adjust voltages for efficient transportation and adaptation to the end user. These equipment use cellulosic materials as insulation, in addition to mineral oil for insulating and cooling purposes. This fluid presents technical and environmental problems due to its fire risk and low biodegradability. To address these problems, biodegradable dielectric fluids with high flash points are being investigated as alternatives to mineral oil. However, they face challenges, such as the impregnation of solid dielectric materials, a critical process in transformer manufacturing. This work seeks to improve the transition towards biodegradable fluids by analyzing solutions to increase the speed of impregnation, such as increasing temperature