Estudio de la capacidad refrigerante de los nuevos líquidos dieléctricos en plataforma experimental y mediante CFD
- Autores: Ramazan Altay
- Directores de la Tesis: Félix Ortiz Fernández (dir. tes.), Fernando Delgado San Román (dir. tes.), Carlos J. Renedo Estébanez (tut. tes.)
- Lectura: En la Universidad de Cantabria ( España ) en 2024
- Idioma: español
- Títulos paralelos:
- Study of the cooling capacity of new dielectric liquids on an experimental platform and using CFD
- Tribunal Calificador de la Tesis: Belén García de Burgos (presid.), Inmaculada Fernández Diego (secret.), Diego Fernando García Gómez (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
En esta tesis se ha realizado el modelado térmico y la réplica experimental de un Transformador de muy Alta Potencia (HPT en inglés) con bobinado en capas. Estos modelos, de carácter teórico (CFD) y práctico (Plataforma Experimental de Orden Reducido (ROTP en inglés), han sido utilizados para analizar el comportamiento termo-hidráulico de varios aceites dieléctricos basados en ésteres en el sistema de refrigeración del Devanado de Baja Tensión (LVW en inglés) de un HPT de 100 MVA, ya que estos líquidos podrían sustituir en el futuro al aceite mineral en esta máquina por su alta biodegradabilidad y su mayor seguridad contra incendios.
- English
In this thesis, thermal modelling and the experimental replica of a very High-Power Transformer (HPT) with layer winding has been carried out. These models, which are theoretical (CFD) and practical (Reduced Order Experimental Platform(ROTP)), are used to analyze the thermo-hydraulic behavior of several dielectric ester-based oils in the cooling system of the Low Voltage Winding (LVW) of a 100 MVA HPT, since in the future these liquids could replace the mineral-based oil in this machine due to their high biodegradability and better fire safety.
Thermal modelling plays a crucial role in understanding the operational dynamics of electrical devices, including power transformers. The temperature distribution within transformers significantly impacts their performance and longevity, particularly affecting the aging process of critical components of the dielectric system, such as the winding insulating paper. As the degradation of this paper often marks the end of a transformer's service life, accurately determining temperature distributions, especially the Hot Spot temperature (HS) within the windings, becomes imperative. This thesis delves into the significance of thermal modelling in assessing transformer health and longevity. Additionally, this thesis introduces a complementary study method: a ROTP that replica the cooling system of the LVW of a 100 MVA HPT is used to evaluate the thermal-hydraulic dynamics of the dielectric liquids under various loading conditions.
Both study methods are used to explore the potential of alternative dielectric liquids, particularly natural and synthetic ester-based liquids, as substitutes for mineral oil in HPT. These alternative fluids offer solutions to the drawbacks associated with mineral oil, including low flash and ignition points, as well as poor biodegradability. By investigating the thermo-hydraulic behavior of these alternative fluids, this thesis aims to contribute to the understanding of their technical viability in HPT applications.
Regarding the CFD studies, two numerical models of the axial cooling system of the LVW of the 100 MVA HPT are developed. The first of them, a 3D model, is used to compare the thermal-hydraulic behavior of two alternative liquids (natural and synthetic ester-based oils) with mineral oil at rated power. The second one, a 2D axisymmetric model, has allowed the same comparison of an ester-based synthetic oil with a mineral oil by considering an ONAN cooling mode with uniform and non-uniform loss distributions. The heat-run test results of the aforementioned HPT with mineral oil and the experimental results of the ROTP with both type of liquids are used to verify the validity of both models. Mass flow rates and HSs are obtained in both studies.
In relation to the ROTP, this thesis presents how this platform was designed: the four different designs considered, the components of the final solution and, finally, the numerical and experimental results with both mineral oil and a natural ester-based liquid that were obtained. The experimental tests were carried out at three power loss levels, with 50%, 75%, and 100% of rated power. The tests at 75% and 100% power losses were initiated immediately after preceding test without any delay.
As summary, several key aspects related with the thermal-hidraulic behaviour of alternative liquids in the cooling system of a HPT have been thoroughly investigated in this thesis. These aspects have been studied using theoretical methods such as 2D and 3D CFD analysis, or by means of experimental methods such as the heat-run test or the use of an experimental platform. As a result of these studies, several general and specific conclusions can be provided: General conclusions - This thesis reveals that the value of the HS and its location in the numerical models depends on the dimensions of the model (2D or 3D), on the type of oil used, and on the input conditions considered.
- It was found that alternative ester-based insulation oils result in higher HS temperatures, which can be explained by their higher viscosity. This is supported by both the results of two different numerical models and the experimental results of the ROTP.
- The increase in temperatures due to the use of ester-based oils in axial cooling systems is not important enough to rule out their use in this type of systems.
- Another significant finding is that the thermal behavior of a very HPT can be successfully replicated using a test platform.
Specific conclusions Heat-run test - An experimental heating test with mineral oil is carried out on a 100 MVA HPT to obtain the HS value in its LVW, which it will be used to validate the numerical models developed.
3D numerical model - HS numerical result is close to those obtained in the heat-run test. That is, the validity of this model can be assumed.
- The location of the HS produced by mineral oil differs from those of the FOSs in the real winding. That is, the sensors are placed in winding layers that do not coincide with the layer where the HS is located in the model.
- Assuming the same inlet temperature and velocity as mineral oil, ester-based oils produced a more uniform mass flow distribution in the channels.
2D numerical model - The HS calculated with this model is different from those of the 3D model and of the heat-run test. In fact, it is significantly lower. This disparity is due to the geometric simplifications that must necessarily be applied in this model: the sticks that separate winding layers are not considered. As a result, there are higher mass flows in the channels, which increases the cooling.
- In contrast, HS location and mass flow distribution are similar to those of the 3D model.
- In both cases, mineral oil and synthetic ester-based liquid, a slight increase in the HS value occurs when a non-uniform loss distribution is considered instead of uniform loss case.
Reduced Order Test Platform - A replica of the LVW of a HPT was successfully designed and built considering the closed loop of cooling. Among the novelties, a flowmeter for low velocities was designed and built, which allows studying ON cases.
- Temperature results from the first tests confirm that the use of alternative liquids represents a slight increase in maximum temperatures compared to those of mineral oil.
- The maximum temperature results measured are close to those obtained in the numerical 3D model or in heat-run test.
Finally, it is necessary to point out that there are still numerous research lines related with the use of alternative liquids in HPT to be explored. For instance: - In this thesis, the layer winding structure was examined. A similar study can be carried out for other winding cooling systems.
- Using the findings of this thesis, existing CFD models can be calibrated and used to create a digital twin of a power transformer.
- The numerical models can also be used to study the effects of different load level on the thermal-hydraulic behavior of the alternative liquids.
- español
