Chemical and spectroscopic characterization of a vegetable oil used as dielectric coolant in distribution transformers

Abstract

Neste trabalho, uma análise espectroscópica completa de UV-Vis, IR e RMN (1 H, 13 C e DEPT) foi realizada para uma amostra de óleo vegetal FR3 ® usada como refrigerante dielétrico em um transformador de distribuição experimental. A mesma análise espectroscópica foi realizada para três amostras de óleo FR3 ® (i.e., com 4 meses de uso, 8 meses e 7 anos de uso), removidas de vários transformadores de distribuição operacional. A comparação entre os dados indicou que não ocorreram mudanças espectroscópicas significativas, e, portanto, não ocorreram mudanças estruturais aos óleos, pelo uso. Transformações químicas como hidrogenação catalítica e hidrólise foram realizadas à amostra de óleo FR3 ® e os produtos obtidos foram analisados por métodos espectroscópicos, a fim de recolher mais informações sobre o óleo FR3 ®. Testes de envelhecimento acelerado em laboratório também foram realizados para as três amostras de óleo FR3 ® , proporcionando informações interessantes sobre a estrutura dos produtos de degradação. Estas informações podem ser valiosas à busca de uma técnica baseada em espectroscopia para monitoramento do tempo de vida e desempenho deste óleo vegetal isolante. In this work, a complete UV-Vis, IR and (1 H, 13 C and DEPT) NMR spectroscopic analysis was performed for a FR3 ® vegetable oil sample used as dielectric coolant in an experimental distribution transformer. The same spectroscopic analysis was performed for three used FR3 ® oil samples (i.e., 4 months in use, 8 months in use and 7 years in use), removed from several operating distribution transformers. Comparison of the data indicated that no significant spectroscopic changes, and hence, no structural changes occurred to the oils by the use. Chemical transformations like catalytic hydrogenation (hardening) and hydrolysis were performed to the FR3 ® oil sample and the obtained products were analyzed by spectroscopic methods in order to collect further structural information about the FR3 ® oil. Accelerated aging tests in laboratory were also performed for three FR3 ® oil samples affording interesting information about the structure of the degradation products. These findings would be valuable to search for a spectroscopy-based technique for monitoring the lifetime and performance of this insulating vegetable oil.

The Tribology of Cleaning Processes

“…Another distinct band was found near 722 cm -1 which is indicative of C-H out-of-plane stretching of saturated carbon-carbon bonds. It was noted that all intense absorptions bands detected in the infrared analysis were in accordance with the typical structure of a triacylglycerol bearing unsaturated fatty acids [23]. In light of this, it can be inferred that the valleys regions of the polymerized soil baked-on stainless steel consisted primarily of vegetable oils.…”

“…The peak at about 1737 cm -1 was assigned to C=O stretching of the carbonyl groups, while the band at 1457 cm -1 originated from CH 2 bending vibrations [24]. The band around 1163 cm -1 is thought to be due ester C-O-C stretching [23]. Another distinct band was found near 722 cm -1 which is indicative of C-H out-of-plane stretching of saturated carbon-carbon bonds.…”

“…Bands at 2924 and 2854 cm -1 represent C-H stretching vibrations of saturated carbon-carbon bonds [23]. The peak at about 1737 cm -1 was assigned to C=O stretching of the carbonyl groups, while the band at 1457 cm -1 originated from CH 2 bending vibrations [24].…”

Photoacoustic spectroscopy as an approach to assess chemical modifications in edible oils

“…The peaks in ultraviolet region (UV) of the absorption spectra of vegetable oils are related to p-p* and the forbidden n-p* electronic transitions due to C=C (non-conjugated double bond) and C=O (carbonyl groups) of unsaturated fatty acids, respectively. [18][19] The thinner band of olive oil and its blue shifted peak in that region is related to higher concentration of unsaturated fatty acids compared to the other two oils. 20 All spectra measured are in the correct range of absorption of fatty acids presents in vegetable oils.…”

Evaluation of the use of a vegetable oil in distribution transformers

“…Are they viable from the economic point of view? In this respect, several studies have been undertaken, mainly by manufacturers of these oils and by some research institutions and universities [6][7][8][9][10][11][12][13][14][15].…”