Abstract
The insulation of mineral oil-based nanofluids was found to vary with different concentration level of nanoparticles. However, the mechanisms behind this research finding are not well studied. In this paper, mineral oil-based nanofluids were prepared by suspending TiO2 nanoparticles with weight percentages ranging from 0.0057% to 0.0681%. The breakdown voltage and chop time of nanofluids were observed under standard lightning impulse waveform. The experimental results show that the presence of TiO2 nanoparticles increases the breakdown voltage of mineral oil under positive polarity. The enhancement of breakdown strength tends to saturate when the concentration of nanoparticle exceeds 0.0227 wt%. Electronic traps formed at the interfacial region of nanoparticles, which could capture fast electrons in bulk oil and reduce the net density of space charge in front of prebreakdown streamers, are responsible for the breakdown strength enhancement. When the particle concentration level is higher, the overlap of Gouy–Chapman diffusion layers results in the saturation of trap density in nanofluids. Consequently, the breakdown strength of nanofluids is saturated. Under negative polarity, the electrons are likely to be scattered by the nanoparticles on the way towards the anode, resulting in enhanced electric fields near the streamer tip and the decrement of breakdown voltage.
Highlights
Nanofluid, i.e., base oil combined with nanoparticles, was firstly proposed by Choi from Argonne National Laboratory in 1995 [1]
The impacts of nanoparticle concentration level on the breakdown characteristics of mineral oil-based nanofluids were investigated in this study
Experimental results show that the polarity effect on breakdown characteristics of nanofluids, caused by accumulated space charges around streamer tips, is reduced by suspending TiO2 nanoparticles
Summary
I.e., base oil combined with nanoparticles, was firstly proposed by Choi from Argonne National Laboratory in 1995 [1]. The positive lightning impulse breakdown voltage of Fe3O4 nanofluid has nearly doubled compared with that of base oil, and the chop time increases from 12.0 μs to 26.0 μs. The mechanism behind the variation in breakdown voltages of nanofluids caused by different concentration levels was not investigated in detail. The impacts of TiO2 nanoparticle concentration level on impulse breakdown performance of mineral oil were carefully investigated. The possible mechanism behind the modification of breakdown voltages caused by the change of TiO2 nanoparticle concentration level is discussed based on electron trapping theory. A possible mechanism is proposed in Section 4 to explain the variation of breakdown performance of TiO2 nanofluids with different concentration Levels.
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