The existence of moisture will lead to lower insulation performance of transformer oil. TiO2 nanoparticles can bind the moisture in transformer oil

which reduces the adverse effects of the moisture. The power frequency breakdown voltage and resistivity of transformer oil and nanofluids under the same moisture content of 40 ppm were tested. The results show that the power frequency breakdown voltage of 10 nm spherical nanofluid is increased by 111.9%

and the modified effect is the most significant. And the breakdown voltages of 5 nm spherical nanofluid and 5 nm rod-like nanofluid are increased by 100.6% and 97.9%

respectively. However

the resistivity of the three kinds of nanofluids is three orders of magnitude smaller than pure oil. But this does not conform to such a phenomenon of electrical insulation as the greater the resistivity is

the higher the breakdown voltage will be. Using the software of Material Studio

the combination mode and distribution state of water molecules with three kinds of nanoparticles are simulated. Accordingly

the improved Stern double layer microscopic model based on the liquid solid interface Gouy-Chapman-Stern model in TiO2 nanofluids is proposed. The surface of the nanoparticles will adsorb water molecules and negative charges in the oil

and eventually form a water film

reducing the probability that a small gas bridge channel produced by electronic collision of water molecules. Moreover

the influence mechanism of size and morphology of nanoparticles on breakdown and conductance characteristics in nanofluids is revealed based on this model.