Читать книгу Alternative Liquid Dielectrics for High Voltage Transformer Insulation Systems - Группа авторов - Страница 57

The Fourier Transform Infrared Spectroscopy (FTIR) analysis is performed to identify the existence of the diverse functional groups in the fresh and aged oil samples. This technique aids in analyzing the uniformity of the oil after degradation in other properties because of temperature and duration. In this process, the infrared (IR) radiation is passed through the oil, out of which some percentage is absorbed and some percentage is transmitted. There are different values of frequencies which indicate different functional groups and thus the resulting spectrum represents the molecular absorption and transmission, creating a molecular fingerprint of the sample. When the IR radiation is absorbed, the molecules of the oil vibrate and it leads to bending or stretching of the bonds. It is observed from studies that the transmittance of the a few natural esters like FR3 and Jatropha (JAT) remain unaffected after aging for 2000 hours at 150 °C [73]. As seen in Figure 2.10a and b, the existence of alkanes is denoted by peaks near to 3000 cm⁻¹ wavenumbers for C–H stretching. For both oils, the existence of esters is indicated by peaks near to 1740 cm⁻¹ for C=O stretching. The CH₂ bending is witnessed at wavenumbers around 1460 cm⁻¹ for both the oil samples. The peaks at 1000–1260 cm⁻¹ for both oil samples for C–O stretching indicate the presence of alcohol. Aging in oil leads to the formation of carbonaceous particles. Nonetheless, the integrity of the oil is intact as all the functional groups are present even after long hours of aging. There is no significant difference observed for a particular oil in various aging times considered. Thus, the FTIR study might provide evidence if the aging is performed for a longer duration. The chemical structure of the oils is not affected but the performance of the oil degrades after aging, as the other thermophysical and electrical properties deteriorate.

Figure 2.10 FTIR spectrum of (a) FR3 aged at 1000 and 2000 hours along with fresh FR3 and (b) Jatropha aged at 1000 and 2000 hours along with fresh JAT.

Source: Baruah et al. [73] / with permission of IEEE.