The propagation velocity of streamer under impulse voltage is an important index to the insulation performance of nano-modified transformer oil and a key parameter for analyzing the modification mechanism. However

most of the existing studies only focus on the breakdown voltage and breakdown time. Therefore

a high quality shooting platform for streamer was built based on Schlieren method. The development of streamers in modified transformer oil by TiO

2

nanoparticles with different shapes and sizes was measured under positive lightning impulse voltages

and then their propagation velocities were calculated to reveal the relation between trap characteristics and streamer propagation velocity. The results show that the change of nanoparticle’s geo

metrical morphology can obviously affect streamer’s development in nano-transformer oil. Rod-like nanoparticles make streamers propagate slower in transformer oil and thus inhibit them. Meanwhile

with the decrease of nanoparticles’ size

streamers’ propagation velocity becomes smaller and their development is suppressed. The reason for this variation of streamer’s velocity is attributed to the influence of TiO

2

nanoparticles’ geometrical morphology on trap characteristics.