Effects of TiO2 Nanoparticles on Streamer Propagation at the Surface of Oil-Impregnated Insulation Paper

Recent studies have found that the surface flashover strength of oil-impregnated insulation paper can be improved by the modification of nanoparticles. To reveal the working mechanism, this paper presents an experimental study on the effects of TiO₂ nanoparticles on streamer propagation process at the surface of oil-based nanofluid-impregnated insulation paper under lightning impulse voltage. The results show that the surface flashover voltage of nanofluid-impregnated insulation paper is significantly increased by 34.6%. Streamer characteristics including shape and length at the surface of oil-impregnated insulation paper were investigated using the schlieren technique. It is indicated that streamer characteristics are dramatically changed by the addition of TiO₂ nanoparticles. For nanofluid-impregnated insulation paper, streamers with more but much shorter branches tend to develop into adjacent nanofluid rather than clinging to the paper compared to that for pure oil-impregnated paper. The reason responsible for the shape dissimilarity lies in the change of electrical force due to the permittivity difference between oil and paper. Furthermore, more shallow traps introduced by nanoparticles contribute to the faster surface charge dissipation of nanofluid-impregnated paper, reducing the charge accumulation at the streamer head and suppressing the electric field distortion. Thus, it is hard for streamers to develop at the surface of nanofluid-impregnated paper, resulting in an increase of surface flashover strength.

I. Introduction

Transformer oil-impregnated insulation paper has been widely used in electrical equipment due to its excellent dielectric property and mechanical strength [1]–[3]. The surface of oil-impregnated insulation paper is usually considered as the insulating weakness, at which a large number of insulation failures are caused by surface flashover discharge [4], [5]. Surface flashover strength of the oil-impregnated paper is closely related to the streamers, which propagate along the surface with an average velocity of ~2 km/s [6]. Generally, breakdown event is caused by the initiation and propagation of streamers as a result of the high local electric field applied to the oil-impregnated insulation paper [7], [8].