Evolution of the thermal and dielectric properties of a transformer vegetal oil enhanced with nanoparticles
- Autores: Cristian Olmo Salas
- Directores de la Tesis: Félix Ortiz Fernández (dir. tes.), Fernando Delgado San Román (tut. tes.)
- Lectura: En la Universidad de Cantabria ( España ) en 2020
- Idioma: inglés
- Títulos paralelos:
- Evolución de las propiedades térmicas y dieléctricas de un aceite vegetal de transformador mejorado con nanopartículas
- Tribunal Calificador de la Tesis: Belén García de Burgos (presid.), Carlos J. Renedo Estébanez (secret.), Ricardo Albarracín Sánchez (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Industrial: Tecnologías de Diseño y Producción Industrial por la Universidad de Cantabria
- Materias:
- Enlaces
- Resumen
- español
Esta tesis afronta la preparación, caracterización y puesta a prueba de cuatro tipos de nanofluidos dieléctricos de base vegetal, preparados con nanopartículas de Fe2O3, TiO2, ZnO y CuO, a concentraciones hasta 1 kg/m3. Preparados siguiendo una metodología de dos pasos, las principales propiedades que condicionan su comportamiento como fluido aislante y refrigerante han sido caracterizadas, en función de la concentración de nanopartículas. Los resultados reflejan como las nanopartículas son capaces de mejorar las propiedades dieléctricas, mientras que su efecto sobre la conductividad, densidad y viscosidad es más limitado, siendo casi nulo en el caso de la primera. Las concentraciones de aquellos nanofluidos con un mayor aumento de su tensión de ruptura has sido seleccionados como óptimas, y muestras de dichos nanofluidos y del fluido base se han utilizado para la refrigeración de un pequeño transformador. Se ha comprobado una mejora de la refrigeración del fluido base exclusivamente con el nanofluido de Fe2O3. Debido a la ausencia de efecto sobre la conductividad térmica, se ha interpretado este hecho en base a la aparición de ciclos convectivos magnetotérmicos.
- English
This research assesses the performance of several nanofluids as cooling and dielectric fluid for electrical transformers, focusing on their main properties.
In the first place, an extensive review of the previous works in this field was done. It is focused on all the aspects that condition the performance of a nanofluid, as the characteristics of its components or the preparation method, and the resulting properties. The applicability of the nanofluids has been also studied. This information has been used as reference and starting point of this work. To be more precise, it has focussed on some of the weaknesses noticed in this research field such as it is the scarce information available about the application of dielectric nanofluids in existing devices, even at laboratory scale. Even more those oils expected to substitute the traditional mineral oils at transformers in the mid-term have been analysed: the biodegradable natural esters.
Four different nanofluids have been prepared, with four different nanoparticles (Fe2O3, TiO2, ZnO and CuO) and a dielectric natural ester as a base, using several concentrations, all of them below 2.0 kg/m3. The preparation method, and the concentrations have been selected according to the knowledge available in the reviewed references. These prepared nanofluids and the base fluid have been characterized from the thermal-dielectric standpoint. According to the standards, they have been determined and compared those properties on which the performance of the fluid depends: breakdown voltage, resistivity, loss factor, density, thermal conductivity and viscosity.
The suitability of each combination nanoparticle-base fluid has been analysed, determining the optimal concentration and identifying those nanofluids most suitable for their testing in an actual electric device. In this sense, considering their dielectric properties, only the Fe2O3 and TiO2 nanofluids shows a better behaviour than the base fluid (in a way according to the literature) while the results with ZnO and CuO nanoparticles are not clear. Respecting the thermal conductivity, none of the combinations studied present higher capacities than the base fluid. The affectation of other properties such as the viscosity or the loss factor is similar to that found in other works. Based on these results, the optimal concentration from the dielectric point of view are 0.2 kg/m3 of Fe2O3 and 0.5 kg/m3 of TiO2. To use them in the following steps, and Despite their erratic behaviour, 0.7 kg/m3 and 0.2 kg/m3 concentrations are chosen for the ZnO and CuO nanofluids, respectively, as the improvement of the dielectric properties is more pronounced with them.
The selected nanofluids and the base fluid have been tested as cooling fluids in an experimental setup. This platform consists in a transformer, immersed in a tank with oil, that feed a resistive circuit (set of rheostats). Inside the tank, the heat transfer is mainly carried out by natural convection. Five sensors are located inside the tank (winding, core, and at the bottom and the top of the tank) and outside, in the laboratory, to measure the temperatures. These probes are controlled, and their temperatures registered, by a microcontroller. By adjusting the resistive circuit, three different load regimes have been set during the tests of the four nanofluids, and the evolution of the temperatures of the transformer has been studied. The results show how while the Fe2O3 nanofluid is able to cool the transformer in a more efficient way, this is not the case with the other nanoparticles, whose performance is, in general, worse than the one showed by the base fluid.
While the improvement in the dielectric properties can be explained by the well-known capacity of some nanoparticles to capture electrons and to delay the propagation of streamers and discharges, the improvement of the cooling capacity that appears in the Fe2O3 nanofluid cannot be explained by a similar theory regarding an enhancement of the thermal conductivity. The magnetic nature of these nanoparticles, together with the absence of this improvement with the other nanoparticles (not magnetic) seem to support the existence of thermal-magnetic buoyancy forces that improve the convection at the tank, due to the interaction magnetic field-nanoparticles.
- español
