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Muhammad Rafq,Yuzhen Lv,Chengrong Li 대한전기학회 2020 Journal of Electrical Engineering & Technology Vol.15 No.1
The Al2O3 nanoparticles (NPs) with favorable features were prepared in our lab to develop transformer oil/paper insulation system with better insulation performance. The nanofuids (NFs) were prepared with diferent shapes (nanorods, nanoplates), surface modifcations (oleic acid, C2, C18) and concentrations (0.6 g/L, 0.8 g/L, 1.2 g/L) of Al2O3 NPs. The positive lightning impulse (LI) breakdown voltages (VBDs) of mineral oil were improved by 1.11 times with nanorod shape, oleic acid surface modifcation and 0.8 g/L concentration of NPs. The efects of Al2O3 NPs with diferent gap distances on insulating properties of NFs under LI voltage were examined. It was noted that after Al2O3 NPs suspension, the positive LI VBDs of transformer oil (TO/MO) were enhanced but the negative LI VBDs of were decreased. The signifcant improvement in insulating performance of NFs is interpreted in light of electron traps theory. It was found that suspended NPs can enhance the shallow trap desity. The generated electrons would lose their kinetic energy through repeatedly trapping and de-trapping process, leading to decline in elcetron mobility. The higher trap density of NPs will lower average energy, and lower mobility of electrons are obtained. The electrons with lower energy are easy to be captured by those molecules with high electron afnity, and be converted into negative space charges. These negative space charge decreases the electrical feld strength at the front of positive streamer and therefore reduce the propagating velocity of positive streamer.