Electronic Properties of Typical Molecules and the Discharge Mechanism of Vegetable and Mineral Insulating Oils

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.

Research and Development of Natural Vegetable Insulating Oil Based on Jatropha curcas Seed Oil

“…In summary, using Jatropha curcas seed oil as the raw material, a high-quality vegetable insulating oil can be prepared by the process designed in this study. Compared with some reported vegetable insulating oil products [9,11,12], the overall performance index of JNIO can meet the requirements of the ASTM standards, and it was better in visual appearance, breakdown voltage, acidity, dissipation factor and viscosity (Table 3). For example, JNIO was clear and bright while the others were usually light yellow or green.…”

“…Studies have indicated that vegetable insulating oil can be used as a substitute for mineral insulating oil in transformers and oil-filled cables [8]. Vegetable oils have excellent electrical properties such as flash points greater than 300 • C, which significantly improves the safety level of the power grid, biodegradation rates of more than 95%-97%, and relative dielectric constants about 1.5 times that of mineral insulating oils [9]. Therefore, as an environmentally friendly product, vegetable insulation oils are increasingly used in related industries [4].…”

“…Parameters such as breakdown voltage, acid value, and dielectric loss need to be improved [10]. At present, vegetable insulation oils are prepared from soybean oil, rapeseed oil, palm oil, Camellia Oil and esters, and so on [9,11,12].…”

Engineering Dielectric Liquid Applications

“…Experimental investigations dedicated towards the performance of natural esters have been presented in [6,7]. Haegele et al [6] reported the degree of inhomogeneity differences in breakdown voltage between natural ester and mineral oils while using lightning impulses at different electrode arrangements representing different fields in homogeneity factors and different gap distances.…”

“…Authors also envisaged different electrode and conductor arrangements reported in the literature for oil breakdown voltage studies. Wang et al [7] discussed the mechanisms characterizing fast and slow streamers in vegetable oil and mineral oil, based on their calculations. The electronic properties of typical molecules were calculated using the quantum chemistry method (B3LYP/6-31G*), based on the density function theory.…”