State Key Laboratory of Power Transmission Equipment & System Security and New Technology, School of Electrical Engineering, Chongqing University, Chongqing 400044, China.
Int J Mol Sci. 2020 Feb 1;21(3):974. doi: 10.3390/ijms21030974.
The effects of C=C, ester and β-H groups on the ionization potential () and electron affinity () of molecules in natural ester insulation oil were investigated by density functional theory (DFT). The major contribution to the highest occupied molecular orbital (HOMO) comes from the carbon atoms adjacent to C=C. Thus, the s of triglycerides decrease as the number of C=C double bonds increases. The C=C in alkanes may also lower the . However, the β-H in triglycerides has little effect on the , and C=C and β-H have only a small effect on the s of the triglycerides because of the major contributions of atoms near the ester group in triglycerides to the lowest unoccupied molecular orbital (LUMO). This study calculated the s of 53 kinds of molecules in FR3, which are significantly lower compared with those of molecules in mineral oil (MO) and trimethylolpropane triester without C=C. However, the lightning impulse breakdown voltage (LI ) of trimethylolpropane triester is still significantly lower than that of MO at the large gap. Therefore, the transition from slow to fast streamers under low lighting impulse voltage is determined by the ester group rather than by C=C and β-H. The ester group may attract more electrons, impacting itself more compared to alkane in MO and facilitating the transition from slow to fast streamers.
采用密度泛函理论（DFT）研究了 C=C、酯基和β-H 基团对天然酯绝缘油中分子的电离势（IP）和电子亲合势（EA）的影响。最高占据分子轨道（HOMO）的主要贡献来自于与 C=C 相邻的碳原子。因此，随着 C=C 双键数量的增加，三酰甘油的 s 值降低。烷烃中的 C=C 也可能降低 EA。然而，由于三酰甘油中酯基附近原子对最低未占据分子轨道（LUMO）的主要贡献，β-H 对 EA 的影响很小，C=C 和β-H 对三酰甘油的 s 值影响也很小。本研究计算了 FR3 中 53 种分子的 s 值，与矿物油（MO）和无 C=C 的三羟甲基丙烷三酯相比，显著降低。然而，在大间隙下，三羟甲基丙烷三酯的雷电冲击击穿电压（LI）仍显著低于 MO。因此，在低照明冲击电压下从慢流光向快流光的转变是由酯基决定的，而不是由 C=C 和β-H 决定的。酯基可能比 MO 中的烷烃吸引更多的电子，与自身的相互作用更多，从而促进从慢流光向快流光的转变。
