Natural ester, as a kind of renewable and environmental insulating material, has created broad opportunities for the development of electrical industry. When it is used in oil-immersed power equipment, it is inevitable to consider the ability of natural esters to withstand electric field breakdown. An increasing number of experiments have studied the breakdown properties of power frequency, direct current and lightning impulse of natural esters. However, the microscopic mechanism of natural ester discharge is still unclear. It can be challenging to improve the application voltage level of natural ester in electrical equipment. In order to better explore the mechanism and principle of natural ester discharge, the effects of electric field on the orbital distribution, electrostatic potential, dipole moment and ionization energy of natural ester were studied by density functional theory. The results show that the highest occupied molecular orbital (HOMO) of triglycerides composed of saturated fatty acids is mainly contributed by the C atom near the carbonyl group, while the lowest unoccupied molecular orbital (LUMO) is contributed by the oxygen atom on the carbonyl group. The HOMO orbital of triglycerides composed of unsaturated fatty acids is mainly contributed by C=C. As the intensity of the electric field increases, the HOMO of the natural ester molecule moves in the direction of the electric field, while the LUMO moves in the opposite direction. Moreover, the energy gap of natural ester decreased greatly with the increase of electric field intensity, but that of saturated triglyceride decreased less than that of unsaturated triglyceride. In the absence of electric field, the maximum electrostatic potential of natural ester molecules mainly exists on the surface of H atom near carbonyl group, while the minimum electrostatic potential mainly exists on the surface of oxygen atom on carbonyl group. With the increase of electric field, the area with negative electrostatic potential of natural ester gradually increased. At the same time, the minimum electrostatic potential of unsaturated triglyceride surface gradually shifted to C=C surface. In addition, with the increase of electric field intensity, the dipole moment of natural ester increases, and the ionization energy of natural ester decreases. This paper provides a theoretical basis for studying the microscopic mechanism of natural ester discharge.

natural ester,frontier orbit distribution,electrostatic potential,density functional theory,ionization energy