Influence of nanoparticles’ polarization on the streamer branching and propagation in nanofluids

•Particle polarization distort the electric field, then induce streamer branching.•Isolated particle with radius less than 800 nm, permitivity less than 30 or far from streamer shell hardly induce branching.•Mutual shielding effect between branches decelerates the propagation of streamers.•The clumped nanoparticles induce streamer branching or change the propagation direction. The mutual shielding effect between branches is thought to be one of the reasons for reduced propagation of streamer in nanofluids. However, the mechanism of how these nanoparticles induce streamer branching in oil is not clear. In this paper, a numerical model was established based on charge carrier continuity equations and field-dependent molecular ionization theory to study the propagation and branching of streamer. The effects of isolated particle with different size, permittivity, and location on streamer branching in oil are discussed in detail. It is found that isolated particle with larger size, or greater permittivity, or closer position from streamer would cause strong enough distortion of electric field around the particle. This changes the ionization distribution during the propagation of streamer to induce a side-branch. To simulate the state of “global uniformity and local clumping” of nanoparticles in nanofluids, a multi-nanoparticle system is established. The local clumped nanoparticles play a synergistic effect on electric field distortion. The reduced electric field, the increased propagating path, and the mutual shielding effect of streamer branches are responsible for the improved breakdown voltage of nanofluids.