Increasing environmental demands influence the requirements for devices and materials used in the power industry. One example is a power transformer and an electro-insulating liquid used in it. In order to meet these requirements, electro-insulating liquids should be characterized by, inter alia, high biodegradability and good fire properties. One of such liquids is natural ester. However, its oxidation stability is low in comparison to mineral oil and demands improvement, which can be achieved by the addition of an antioxidant. The authors of this work used fullerene nanoparticles for that purpose. Pure natural ester samples were prepared, and samples with two concentrations of fullerene, 250 mg/L and 500 mg/L in natural ester. All these samples were aged in a thermal oxidation process. Thereafter, the aging properties of all the samples were compared to assess the oxidation stability of modified liquids. Moreover, the electrical properties of prepared insulating liquids were investigated to assess if fullerene deteriorates these properties after aging process. Based on the obtained results, it was proved that the aging process slowed down in the case of both fullerene concentrations in ester. The acid number of natural ester modified using fullerene was lower than in the case of pure liquid.

The main objective of the research was to analyze the influence of natural ester aging conditions on its neutralization value (acidity) in terms of the limits given in IEC 62975. To achieve this goal, accelerated hydrolytic and oxidative aging of the natural ester was carried out. The properties of the natural ester were tested before and after the aging process, such as acidity, water content, interfacial tension, breakdown voltage, and dielectric dissipation factor. Moreover, using a gas chromatograph coupled with a mass spectrometer, fatty acid analysis was performed. The research results presented in the article showed that both hydrolytic and oxidative aging of the natural ester leads to the formation of free acids, which causes an increase in the acidity. Analysis of saturated and unsaturated fatty acids in the natural ester allowed for the explanation of changes in the ester properties. The article shows that in the case of hydrolytic aging, an increase in the acidity does not have to be accompanied by a deterioration in the other properties of the natural ester, and in such a case ester reclamation may not be necessary.

Artykuł dotyczy wybranych zagadnień związanych z zastosowaniem estrów naturalnych w transformatorach energetycznych. Przedstawiono zalety i wady tych cieczy. Wskazano jedno z głównych ograniczeń w ich stosowaniu związane ze słabą stabilnością oksydacyjną. W artykule opisano możliwości ograniczania procesu oksydacji estru naturalnego poprzez jego modyfikację przy użyciu fulerenu C60. Uzyskane wyniki badań potwierdziły możliwość rozpuszczenia fulerenu w estrze naturalnym oraz ograniczenia procesu utleniania estru.

One possibility to improve the parameters of insulating liquids is their modification by means of nanopowders. The improvement of the dielectric fluid parameters depends on the type and size of the nanopowder as well as on the method of nanofluid preparation. Research conducted around the world are mainly focused on improvement the electrical strength and thermal conductivity of modified insulating liquids. The article presents an overview of nanomodifiers, methods of nanocolloids preparation and the issues related to their stability.