Abstract
Evaluation of insulation strength for lightning surge that actually enters into substations is important to estimate insulation reliability of gas-insulated equipment. The standard lightning impulse voltage (1.2/50μs) is used for factory tests. However, the actual lightning surge waveforms in substations are complex and are usually superimposed with various oscillations. Insulation characteristics of SF6 gas against such complex voltages have not been sufficiently clarified.
This paper deals with gap breakdown characteristics in SF6 gas under sub-microsecond pulses. Breakdown voltages are lower under a polarity reversal case than under a mono polarity case. The cause of this difference is discussed with a observing discharge propagation using an image converter camera. Moreover the electrode size effect is also discussed.
