Abstract
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.
Highlights
Vegetable insulating oil is a nontoxic, reproducible and environmental dielectric fluid [1,2,3,4,5,6,7]
The ionization potential (IP) theoftypical molecules are calculated by quantum chemistry methods based on density density functional theory
1-methylnaphthalene and eicosane are selected as the typical molecules in
Summary
Vegetable insulating oil is a nontoxic, reproducible and environmental dielectric fluid [1,2,3,4,5,6,7] It can be used as a substitute for mineral insulating oil, in transformer and oil-filled cables [8,9,10,11]. The basic physical, chemical and electrical properties of vegetable oil and mineral oil are listed in Table 1 [3]. It is attracting increasing research interest due to its high fire point of above 300 ◦ C [4], which significantly improves the safety level of the power grid. Vegetable oil absorbs the moisture in insulation paper, leading to much more prolonged lifetime of oil-paper insulations [7]
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