Abstract
The use of nanofluids as dielectric liquids for transformer insulation has been widely investigated during the last decade. A number of authors have performed extensive studies on liquids produced from different types of nanoparticles and base fluids, providing evidence of their good dielectric properties. Nevertheless, nanodielectric fluids are still at the research stage, and they are far from being a solution that can be applied to real transformers. One of the aspects that might be clarified is their compatibility with the rest of the materials present in the transformer and their behavior throughout the life of the equipment. This paper studies the aging process of cellulose impregnated with an ester-based nanofluid and compares it with the process that takes place when the impregnation liquid is a natural ester. Accelerated aging experiments were performed, and physical and chemical characterization of the process with several analytical techniques was carried out. The mechanical degradation of the cellulose was studied in terms of tensile strength, and the evolution of moisture in the paper and oil was monitored throughout the aging process. The study was completed with FTIR and XPS tests aimed at studying the chemical changes of the materials during the aging process. The experimental results suggest that the degradation rate of the cellulose is not significantly affected by the presence of nanoparticles. However, the XPS study revealed that the chemical reactions involved in the degradation processes of both types of insulation might differ. Several mechanisms are proposed in this work.
Highlights
The insulation system is one of the most important parts of a power transformer; failures in this system may lead to serious problems in transformer operation that could compromise the stability of the power system [1,2]
The most commonly used liquid insulation is mineral oil (MO), which is derived from petroleum, in recent years, natural and synthetic esters are becoming popular for transformer insulation purposes
It can be observed that the tensile strength measurements (TS) values measured for the samples of paper immersed in NF are slightly lower than those of the paper immersed in natural ester (NE) for the same aging times
Summary
The insulation system is one of the most important parts of a power transformer; failures in this system may lead to serious problems in transformer operation that could compromise the stability of the power system [1,2]. The most commonly used liquid insulation is mineral oil (MO), which is derived from petroleum, in recent years, natural and synthetic esters are becoming popular for transformer insulation purposes. Another innovation that has recently been explored is the possibility of using nanofluids (NF) as liquid insulation in transformers. These liquids are produced by adding small amounts of nanoparticles (NP) to a base fluid that can be an MO or a natural or synthetic ester. NFs have attracted substantial attention, as they exhibit an improvement in some key thermal or dielectric properties [4,5,6], which could lead to the design of smaller and more efficient transformers in the future [7]
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