Effects of molecular structure on the physical, chemical, and electrical properties of ester‐based transformer insulating liquids

This article presents the experimental studies carried out on the environmental friendly polyol ester insulating liquids to investigate the effect of molecular structure on the physical, chemical, and electrical properties. Six different polyol esters that can be produced from the transesterification of various methyl esters with neopentylglycol/trimethylolpropane alcohols were synthesized and compared with those of refined, bleached, and deodorized palm oil (RBDPO) and mineral transformer oil. The finding suggests that the physical properties like fire point, pour point, and viscosity are very much affected by the molecular weight and molecular composition of the polyol esters. The electrical properties are also highly influenced by the molecular structure‐related characteristics, such as the polarity, dipole polarization, carbon chain length, and degree of branching. The results confirm the findings of previous studies that the polyol esters and RBDPO have more polarity and dipole polarization compared to mineral oil. The experimental evidence showed that the newly synthesized insulating liquids have favorable thermal and electrical properties, thus suggesting that the insulating liquids have the potential to replace conventional insulating liquids to provide a more sustainable power system in the future

Electrical and physicochemical properties of mineral and vegetable oils mixtures

International audienceThis work is devoted to the study of electrical and physicochemical properties of naphthenic mineral oil and natural ester olive oil mixtures; seven mixtures with different mineral oil/vegetable oil ratios are considered. The main investigated properties are breakdown voltage, density and charging current response. All the physicochemical properties measurements are achieved in respect with IEC standards. DC charging currents are measured thanks to a programmable electrometer (Keithley 617 type) for long field application duration. The main task concerns the search of the best mixture or at least the ratios that are in accordance with international standards requirements to be used in transformers with comparable properties as that of new mineral oil. The advantages of each of them will be discussed in relation with the main required properties

The effect of water content on the electrical properties of transformer oil

The condition monitoring of insulating oil used in high voltage apparatus is based on assessing its electrical, physical and chemical properties. During their service life, these apparatuses such as transformers are subjected to several stresses which reduce their insulating capacity. Water and oxygen are the most important factors that accelerate the aging and degradation of transformer oil. There is a strong relationship between the presence of water in oil and the degradation of its electrical properties. This paper presents an experimental investigation to quantify and correlate the change in water content in transformer oil and its effect on their electrical properties. For this purpose, three samples of oil are used: new uninhibited, regenerated and used oil. A physical treatment using a MAXEI station is applied to the three samples to reduce their water content. The treatment is an operation of filtration, degassing and dehydration which is a necessary step before injection of the oil in transformer and during maintenance operations. During the physical treatment, the electrical properties of the oil samples are measured. The breakdown voltage, the dielectric loss factor, the permittivity and the resistivity were measured in according to the standards IEC 60156 and IEC 60247. The results revealed that for the three oil samples; new, regenerated and used, the electrical properties are strongly correlated with the change in water content in oil. The breakdown voltage and resistivity increase considerably when the water content is reduced. If the water content is reduced under 5 ppm, the breakdown voltage remains practically constant. The dielectric loss factor decreases by the water content variation. By decreasing the water content in oil, the insulating properties of transformer oil are improved. The analysis of the results shows that a strong correlation exists between the breakdown voltage, resistivity and the presence of water in oil