Abstract
SF6 is the most commonly used insulating gas for the electric power apparatus, because of its superior dielectric and chemical properties. On the other hand, it is said that breakdown voltage in SF6 under nonuniform electric field would be significantly decreased. So, gas mixtures with SF6 have been investigated as substitutes for SF6 nowadays.
We observed current pulse waveforms, light intensity waveforms and light images of PD in different pure gases and gases mixed with SF6. As a result, we found that PD in different pure gases had different characteristics based on the physical properties of gases themselves. In the case of gas mixture with SF6, the PD characteristics differed with that of pure gases, and approached to that of pure SF6 drastically. Moreover, we examined the PD extension length and calculated electric field on the tip of PD. As a result, the extension length of PD tends to be decreased as the content of SF6 increased. On the other hand, the electric field on the tip of PD approached to critical electric field in pure SF6. Thus, the PD characteristics in gas mixture change greatly into that of pure SF6. This is the reason why the breakdown characteristics in gas mixture with SF6 change drastically with small content of SF6.
