Prácticas educativas familiares y rendimiento escolar en el área de lenguaje: comunicación y representación en niños y niñas de 4 años

El estudio se centra en la relación existente entre los estilos educativos familiares: autoritario, equilibrado y permisivo; y el rendimiento académicos de los niños y niñas del segundo ciclo de educación infantil (4 años) en el área del lenguaje. Para dicho estudio he tomado como referencia los estilos educativos familiares propuestos por Baumrind (1971), Gracia y Musitu (2001) y Alonso y Román (2003). Y los estudios realizados por Musitu, Román y Gutiérrez (1996) de la relación entre el estilo educativo familiar y el rendimiento académico. Han participado 12 sujetos pertenecientes a familias nucleares, realizándoles una entrevista, para ello, se ha usado una escala PEF- Escala de identificación de “prácticas educativas familiares” y una escala ordinal de medida en relación al rendimiento de los sujetos en el área del lenguaje. Se puede destacar como a través de la investigación se ha detectado que el estilo educativo predominante en las familias es el equilibrado. Se han propuesto unas pautas de intervención para la adecuada actuación de los padres.Grado en Educación Infanti

Numerical and experimental evaluation of dielectric properties of thermally aged insulating paper used in power transformers

Due to the relevant role of the cellulosic insulation in the dielectric system of a power transformer, it is necessary to know its dielectric properties and its evolution as insulating material. The dependence of the dielectric properties of solid insulation on the moisture content, temperature, or pressure is well-defined. However, it is not clear the effect of the paper degradation on its insulating capacity. To study the impact of ageing on the dielectric properties, samples of Kraft paper were subjected to an accelerated hygrothermal ageing. Degree of polymerization (DP) value was reduced from 1000 to 200, with intermediate study points. All samples were conditioned to the same moisture content in order to only evaluate the effect of the paper degradation. Different dielectric properties, such as loss factor (tanδ) and complex permittivity (ε) were measured using the dielectric spectroscopy technique. These experimental results were used to develop a numerical model with the finite element-based tool Comsol Multiphysics. This model provided some extra information about the material properties, such as the electric field distribution. Results showed that the degradation of Kraft paper modifies its dielectric response.We acknowledge the support of the Spanish Ministry of Science and Innovation by means of the National Research Project Asset management of biodegradable-fluid-based transformers (PID2019-107126RB-C22/AEI/ 10.13039/501100011033). The authors also wish to thank “Fundación Iberdrola” for its financial support for the research project: S090 “Análisis de las Propiedades Dieléctricas de Aislamientos Sólidos Impregnados con Líquidos Dieléctricos”. C. Méndez also wants to acknowledge the Spanish Ministry of Science, Innovation and Universities for the financial support for the FPU grant (FPU19/01849)

Estimating the age of power transformers using the concentration of furans in dielectric oil

Transformers have an insulation system based on dielectric oil and paper. Several factors as shortcircuits, high load, or overheating influence the aging of the insulating system. Thus, these materials are decomposed during transformer operation, and its state determines the status of the transformer. The degree of polymerization of dielectric paper is an indicator of its real condition. The concentration of furanic compounds in oil offer an estimation of paper degradation. Moreover, these compounds are easy to measure from oil samples. This paper review equations which relate one or more properties of the insulating system with the life expectancy of the transformer. These equations were used in a fleet of transformers in order to estimate the accuracy of these mathematical models. Results show that these methods achieve the most reliable estimation when the transformers have operated less than 8 years. Nevertheless, when the transformers are older, the estimation of lifetime based on furanic compounds is quite erratic and should be improved.The research leading to these results has received funding from multiple sources during years but we would specifically like to acknowledge the support received in the later stages from the Spanish Plan Estatal de I+D under the grant agreement DPI2013-43897-P

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)

Titania nanofluids based on natural ester: cooling and insulation properties assessment

The assessment of a TiO2 vegetal-based dielectric nanofluid has been carried out, and its characteristics and behavior have been tested and compared with a previously tested maghemite nanofluid. The results obtained reflect a similar affectation of the main properties, with a maximal improvement of the breakdown voltage of 33% at 0.5 kg/m3, keeping the thermal conductivity and the viscosity almost constant, especially the first one. This thermal characterization agrees with the results obtained when applying the TiO2 optimal nanofluid in the cooling of an experimental setup, with a slightly worse performance than the base fluid. Nevertheless, this performance is the opposite to that noticed with the ferrofluid, which was capable of improving the cooling of the transformer and decreasing its temperature. The similarities between the characterizations of both nanofluids, the differences in their cooling performances and their different magnetic natures seem to point out the presence of additional thermomagnetic buoyancy forces to support the improvement of the cooling.This research is under BIOTRAFO project—“Raising Knowledge and Developing Technology for the Design and Deployment of High Performance Power Transformers Immersed in Biodegradable Fluids,” which has received funding from the European Union Commission’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement H2020-MSCARISE-2018- 823969; 2019-21. The authors of this research wish to thank the Spanish Ministry of Economy for its financial support for the National Research Project: “Improvement of Insulation Systems of Transformers through Dielectric Nanofluids: Thermodynamic Characterizations and Modelling” (DPI2015-71219-C2 1-R). Additionally, they want to thank the Regional Government of Cantabria; more precisely, the Department of Universities, Research, Environment and Social Policy, for its financial support for the Project “Fluidos Biodegradables en Transformadores Eléctricos de Potencia: Impregnación de Dieléctricos Sólidos y Modelado Térmico con THNM.” Mr. Olmo would like to acknowledge to the University of Cantabria and the Government of Cantabria for the financial support for the Ph. D. scholarship (CVE-2016-6626)

Effect of TiO2 nanoparticles on the performance of a natural ester dielectric fluid

Mineral oil has been frequently used in most of high voltage transformers. However, this oil has started to be replaced by vegetable oils. Additionally, different authors have found that mineral oil-based nanofluids have a potential in improving insulating properties of transformer oil. In order to improve the characteristics of a commercial vegetal oil, this work has used TiO2 nanoparticles to obtain a nanofluid whose ageing behavior at 150°C for 300 hours has been studied.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)

Ageing of crepe paper in mineral oil and natural ester

Several billion liters of transformer oil are used in oil filled transformers worldwide. These machines are voltage transformation devices in which during their operation the heat of windings and iron core firstly is transferred to the insulation oil and then to the cooling medium. Currently, this type of transformers mainly utilizes mineral oils due to their proven good service performance. However, mineral oil has certain limitations such as their low flashpoint and biodegradability which conditions its use in indoor environments, and it may cause a high environmental impact during its use. The development of biodegradable liquids (synthetic and natural esters) has provided an alternative. Nevertheless, a question arises when natural esters are used in power transformers, are they compatible with the rest of materials used in their design. Nowadays, although several studies of accelerated thermal ageing have been undertaken there are few works that study the impact of insulation liquid and temperature on the degradation rate of other cellulosic materials such as crepe paper. This paper can take different shapes of the surface being insulated and has greater surface area which allows to retain more oil reducing the working temperature of the transformer. For this reason, this work has compared the impact of the type of insulation oil (a mineral oil and a natural ester) and the temperature (150o C, 130oC and 110oC) on lifetime of this insulation paper. Degree of polymerization has been measured to quantify the effects. Additionally, the degradation suffered by insulation oils has been evaluated through the measurement of acidity, dissipation factor and DC resistivity. It has been found that the degradation suffered by natural ester is higher than mineral oil, however, the biodegradable liquid extends the life of crepe paper.This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 823969

Maghemite nanofluid based on natural ester: cooling and insulation properties assessment

The objective of this work is to study the effect that the addition of magnetic nanoparticles to a natural ester has on its properties and its cooling capacity. Some samples of ferrofluid (natural ester with maghemite) have been prepared using different concentrations. These have been characterized by measuring their thermo-hydraulic and dielectric properties, to find an optimal concentration. Then, the cooling capacities of the optimal nanofluid and the base fluid have been tested in a transformer immersed in these liquids. The experimental platform allowed the measurement of temperatures in different locations at different load levels. Parallel simulations of these tests have been carried out with a Computational Fluid Dynamics model of the experimental platform. The results show an improvement of the insulating capacity of the base fluid with the addition of maghemite nanoparticles, and an enhanced cooling capacity.This work was supported in part by the European Union’s Horizon 2020 Research and Innovation Programme through the Marie Sklodowska-Curie under Grant 823969, and in part by the Ministry of Economy through the National Research Project: Improvement of Insulation Systems of Transformers through Dielectric Nanofluids under Grant DPI2015-71219-C2 1-R. The work of C. Olmo was supported by the University of Cantabria and the Government of Cantabria through Ph.D. Scholarship under Grant CVE-2016-6626

Cooling performance of different dielectric fluids containing nanoparticles in a transformer winding

This work presents a study where the thermal performance of different nanofluids is tested in a transformer winding model. A 2D axisymmetric non-isothermal CFD model has been used to compare temperature and velocity distribution of the proposed fluids. The fluids tested consists of eight different mixtures manufactured from two different nanoparticles and two different concentrations, using a mineral oil and a natural ester as base liquids. The comparison has been carried out between each nanofluid and their base fluid to observe the thermal impact of nanoparticles. The temperature dependent properties have been determined to include them in the simulation model. Two different inlet velocities were selected as inlet conditions, representing Oil Natural and Oil Directed Cooling. The analysis has been carried out using ANSYS Fluent ® in a two pass winding model. The average and maximum disc temperatures and mass flow distributions are obtained for all the cases. The results obtained show that the temperature in the seven discs of the considered winding increases when the nanoparticles are added to the natural ester, between 3 and 7%. On the other hand, in the case of mineral oil, the addition of nanoparticles reduces the temperature in the discs between 0.3 and 3%.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)