The effect of nanoparticles on streamer propagation in transformer oil under lightning impulse voltage

This paper deals with the understanding of how the nanoparticles affect the electrical performances of transformer mineral oil under lightning impulse voltage. The streamer propagation in pure oil and nano-oil is investigated under both positive and negative lightning impulse voltages. The experimental results show that Fe
₃
O
₄
, conductive nanoparticles, have a polar effect on the development of streamers and breakdown voltage. Under positive voltage, the stopping length of streamers in Fe
₃
O
₄
-modified oil are shorter than those in the pure oil at the same voltage amplitude, and the breakdown voltage in nano-oil is higher than that in pure oil. In contrast, under a negative voltage, the stopping length of streamers in Fe
₃
O
₄
-modified oil are longer than those in the pure oil and breakdown voltage is lower. However, this effect is only observed in Fe
₃
O
₄
-modified oil; insulating nanoparticles Al
₂
O
₃
have little effect on the stopping length of streamers and breakdown voltage whether under positive or negative impulses. With regard to the structure of streamers, differences in the streamers morphology are observed depending on the voltage polarity. Most of the positive streamers are branched at the beginning, but the bifurcation positions in the negative streamers are more random. At the same time, the light emitted by positive streamers is weaker than that emitted by negative streamers.