The research of discharge dispersion of SF6 breakdown voltages with the size of electrodes under lightning impulse

Generally, as using the up-and-down method to research the discharge character of SF
₆
under impulse voltage, the requirement for dispersion of breakdown voltage is less than 3%, which guarantees the reliability of experimental data. But it is found that the dispersion of SF
₆
breakdown voltage, comparing with other gases, is usually large and even larger than 5%. This research has been still lack of systematic studies. Therefore, the changing law of SF
₆
breakdown voltage dispersion with electrode sizes and gas pressures under positive and negative standard lightning impulse (LI) is discussed in this paper. The results show that when gap length d=33 mm and radius of electrode r=40, 15, 8 mm, the dispersion is lower as the pressure grows. The changing trend of dispersion, as the field non-uniformity factor grows, is alike “U” curve trend under positive impulse, which is declining at first and then growing. And the changing trend of dispersion is alike inverse “U” curve trend under negative pulse, which is declining at first and then growing.