Breakdown strength of air, SF6and a mixture of air plus SF6containing a small amount of SF6

Abstract

AbstractThe breakdown strengths of dry air, sulphur‐hexafluoride (SF6) and a mixture of dry air plus SF6containing 1% of SF6were studied. For this purpose, 50‐Hz AC and lightning impulse breakdown voltages in uniform and non‐uniform fields up to a pressure of 400 kPa were measured. The results show that the addition of 1% of SF6to dry air increases considerably the breakdown voltage in a non‐uniform field. By the aid of breakdown voltage versus pressure curves the relative breakdown strength of the mixture with respect to components was calculated both in 50‐Hz AC and lightning impulse voltages. The analysis of Paschen curves reveals a slight improvement of breakdown strength in the case of mixture but in non‐uniform fields the maximum AC breakdown voltage of the mixture is slightly lower than that of pure SF6. However, for positive lightning impulses maximum breakdown voltage of the mixture was found to be greater than that of pure SF6alone.