Vegetable insulating oil may replace the mineral insulating oil used in large power transformers due to its extraordinary biodegradability and fire resistance. According to component analysis, 1-methylnaphthalene and eicosane are considered the typical molecules in mineral oil. Triolein and tristearin are considered the typical molecules in vegetable oil. The ionization potential (IP) and the variation of highest occupied molecular orbital (HOMO) of typical molecules under an external electric field are calculated using quantum chemistry methods. The calculation results show that the IP of the triolein molecule is comparable to that of the 1-methylnaphthalene molecule. The mechanisms of losing electrons are discussed, based on the analysis of HOMO composition. The insulation characteristics of the triolein and tristearin are more likely to be degraded under an external electric field than those of 1-methylnaphthalene and eicosane. Due to the fact that the number density of low IP molecules groups in vegetable oil is much greater than that in mineral oil, the polarity effect in vegetable oil is more obvious than that in mineral oil. This eventually leads to different streamer characteristics in vegetable oil and mineral oil under positive polarity and negative polarity.

No abstract

A family of oligofluorene-type pendant conjugated molecules (C1 and C2), consisting of triazine center with two diphenylamine and one carbazole heterogeneous substituents to form donor-acceptor (D-A) core structure, are synthesized...

No abstract

Natural ester has been widely studied as an alternative dielectric liquid to mineral oil in recent years. Unsaturated triacylglycerol molecules are the main components of natural ester; therefore, in this paper, we investigate the molecular structure and electronic properties of the triolein molecule, an oleic-type triacylglycerol molecule, as a representative component of natural ester oils. The effects of external electric fields at the electric field intensity related to streamer initiation and propagation on the bond lengths, dipole moment, total energy, infrared spectra, and orbital energy of the triolein molecule are investigated using density functional theory (DFT). In addition, the excitation energies, transition wavelengths, and oscillator strengths of the first eight excited states of the triolein molecule under external electric fields are calculated by time-dependent DFT. The results show that the bond lengths, dipole moments, total energy, and infrared spectra change obviously under external electric fields. With increasing external electric field intensity, the energy of the highest occupied molecular orbital increases, and the gap between that and the energy of the lowest unoccupied molecular orbital decreases, which make the molecule susceptible to excitation. The calculations contribute to an understanding of the causes behind the degradation of the insulation properties of natural ester oils.