Tu Youping

Breakdown characteristics of CF 3 I and CF 3 I/N 2 gas mixtures in uniform field

With its high insulation capability and excellent environmental friendliness, CF₃I has been considered as a potential substitute to SF₆. However, considering its high boiling point, CF₃I should be mixed with buffer gases such as CO₂ or N₂. In this paper, breakdown performance of CF₃I/N₂ gas mixtures, SF₆/N₂ gas mixtures and pure SF₆ gas in uniform field are investigated, with negative dc voltage or negative lightning impulse voltage applying. DC breakdown experiments of pure CF₃I gas and pure SF₆ gas show that the dielectric strength of CF₃I is not always higher than that of SF₆. The insulation experimental results show that in low pressures, 30%CF₃I/70%N₂ gas mixtures present similar insulation properties as 20%SF₆/80%N₂ gas mixtures. Considering liquefaction temperature and insulation properties, 30%CF₃I/70%N₂ gas mixtures could be possible substitutes to SF₆ or SF₆/N₂ gas mixtures in low pressures, and it is significant to study their insulation strength in higher pressures.

Influence of nanoparticles on the surface discharge marks in oil-pressboard insulation

It recently has shown that nanoparticles can improve the electric properties of transformer oil when it is added in the oil. This paper investigated the effects of nanoparticles on oil impregnated pressboard in terms of the surface discharge development, the surface tracking marks, and the material trapping properties. It is found that the nanoparticles can increase the shallow trap density in the oil impregnated pressboard, resulting in less carbonized tracking marks on the pressboard surface.