Effect of the thermal characteristics of dielectric fluids on the loading capacity of a power transformer

The use of biodegradable dielectric liquids in power transformers has several advantages, such as increased fire safety or their biodegradability in the event of a leak in the tank. However, they also have a higher viscosity that does not benefit their cooling function within these machines. Although there are many references that analyze the transformers hotspot temperature for dynamic loading, there are hardly any references that focus on the dynamic evaluation of the hotspot when the viscosity of the dielectric and cooling fluid changes, with respect to that of the oil of mineral origin. In this work, the algorithms proposed in the bibliography will be combined with the use of computational fluid dynamics software ANSYSFLUENT, which uses the finite volumes method to solve the equations that govern fluid flow. The software tool will be used to calculate the temperatures of a 100MVA transformer winding. Once these temperatures have been calculated, they can be entered into the hotspot temperature estimation algorithm when the machine's load regime is varied. This analysis will be repeated using dielectric liquids with different thermal characteristics. Transformer fleet managers may use the results of this study in order to adapt their procedures when the machines they manage do not have conventional mineral oil insidePart of the work was performed during secondments between University of Valle and the Universidad de Cantabria executed in the framework of the BIOTRAFO project “Raising knowledge and developing technology for the design and deployment of high performance power transformers immersed in biodegradable fluids”, H2020-MSCARISE-2018-823969, 2019–21. 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. Also, 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 want to thank the grant received from the Call for the Development of the 2020 Industrial Doctorate Program of the Universidad de Cantabria

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)

Electrical installation of a residential building

Grado en Ingeniería Eléctric

Mineral and ester nanofluids as dielectric cooling liquid for power transformers

Amidst the new techniques facing the improvement of cooling and insulating efficiency and the design of electric transformers, constrained by the current technologies, one of the more promising is the substitution of traditional dielectric oils for nanofluids. Research on nanofluids for their application in transformers as a coolant and dielectric medium have been performed during the last two decades and continue today. This review tries to collect and analyze the available information in this field and to offer it already dissected to researchers, focusing on the preparation methods and how nanoparticles affect the main properties of the base fluids. Here we also addressed the influence of different parameters as particle characteristics or environmental conditions in nanofluids performance, the evolution with time of the measured properties, or the neighboring relationship of nanofluids with other transformer components. In this sense, the most reviewed articles reflect enhancements of thermal conductivity or dielectric strength, as well as an improvement of time evolution of these properties, with respect to those that are found in base fluids, and, also, a better interaction between these nanofluids and dielectric cellulosics. Thus, the use of dielectric nanofluids in transformers may allow these machines to work safer or over their design parameters, reducing the risk of failure of the electrical networks and enhancing their life expectancy. Nevertheless, these advantages will not be useful unless a proper stability of nanofluids is ensured, which is achieved in a small part of revised articles. A compendium of the preparation methodology with this aim is proposed, to be checked in future works.This research was funded by 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). C. Méndez also wants to acknowledge the Spanish Ministry of Science, Innovation and Universities for the financial support for the FPU grant (FPU19/01849)