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To further understand the influence mechanism of nanoparticles on oil-paper insulation in transformer, this paper presents experimental research on streamer propagation of 5 nm, 10 nm, 15 nm spherical TiO2 nanofluids-impregnated pressboards (NPs) and pure oil-impregnated pressboards ( OPs ) under positive standard lightning impulse voltage. The streamer propagation images at the interface of all samples were shot from the side, based on the shadowgraph technique. It is shown that the three types of TiO2 nanoparticles can inhibit the velocity of positive streamers and accelerate the dissipation progress. The interface streamer branches of the NPs are more clustered and the trends of the streamer heads are more inclined to the oil, attributed to the nanoparticles. The modification effect is better with the smaller size of the nanoparticles. The steamer stopping length of 5nm NPs is 32.6% lower than that of OPs. It is because a large number of shallow traps will be introduced after the addition of TiO2 nanoparticles. On the one hand, the shallow traps adsorb the high-speed electrons in plasma to form low-speed negative ions. Therefore, the probability of charge recombination at the streamer head is increased. On the other hand, the spacing between shallow traps becomes smaller, forming shallow traps band area. The charges are transported in shallow traps band, increasing the charge mobility and inhibiting the accumulation of space charge. These two effects make the electric field decrease at the streamer head. The specific surface area of nanoparticles increases with the decreasing size, result in more shallow traps and better modification effects.
Inspec keywords: nanofluidics; titanium compounds; nanoparticles; space charge; discharges (electric); transformer oil
Subjects: Organic insulation; Dielectric materials and properties