Abstract
Surface charge accumulation on epoxy insulators is one of the most serious problems threatening the operation safety of the direct current gas-insulated transmission line (GIL), and can be efficiently inhibited by the surface modification technology. This paper investigated the mechanisms of fluorination modulated surface charge behaviors of epoxy resin through quantum chemical calculation (QCC) analysis of the molecular structure. The results show that after fluorination, the surface charge dissipation process of the epoxy sample is accelerated by the introduced shallow trap sites, which is further clarified by the carrier mobility model. The electron distribution probability of the highest occupied molecular orbitals (HOMO) under positive charging and the lowest unoccupied molecular orbitals (LUMO) under negative charging shows distinctive patterns. It is illustrated that electrons are likely to aggregate locally around benzenes for the positively charged molecular structure, while electrons tend to distribute all along the epoxy chain under negatively charging. The calculated results verify that fluorination can modulate surface charge behaviors of epoxy resin through redesigning its molecular structure, trap distribution and charging patterns.
Highlights
With the development of high-voltage direct current (HVDC) transmission, the gas-insulated transmission line (GIL) has been put into application all around the world [1,2,3]
Under the unipolar electric field, charges tend to deposit on the insulator surface during the long-term operation of the GIL, making the gas/solid interface the weak part of the whole system [4,5,6,7]
As one of the main concerning topics, surface characteristics of the insulators are in urgent need to be improved, in which the structures of the epoxy resin play an extremely important role [10,11,12,13]
Summary
With the development of high-voltage direct current (HVDC) transmission, the gas-insulated transmission line (GIL) has been put into application all around the world [1,2,3]. Under the unipolar electric field, charges tend to deposit on the insulator surface during the long-term operation of the GIL, making the gas/solid interface the weak part of the whole system [4,5,6,7]. As one of the main concerning topics, surface characteristics of the insulators are in urgent need to be improved, in which the structures of the epoxy resin play an extremely important role [10,11,12,13]. Surface fluorination technology has been proved to be efficient for the modification of polymer materials in various researches, showing priorities of the simple operation and the low cost [14,15,16]. The regulation of the charge transport process can Molecules 2020, 25, 3071; doi:10.3390/molecules25133071 www.mdpi.com/journal/molecules
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