Impulse Breakdown Voltage-Time Curves of SF6 and SF6 - N2 Coaxial-Cylinder Gaps

The paper constitutes a systematic theoretical and experimental investigation into impulse breakdown voltage time curves of coaxial-cylinder gaps in SF6 and 50% SF6-50% N2 mixture. The breakdown time delay probability is treated as a bivariate distribution in statistical and formative time lags. A method is developed to deduce the marginal breakdown voltage probability curve from statistics of time delay. The experimental work was performed on a 2.54/7.0 cm diameter 60 cm long coaxial-cylinder electrodes using SF6or SF6-N2 mixture pressures of 0.1-0.3 MPa subjected to 0.5/50 ??s and 1.2/50 ??s impulses of both polarities, covering breakdown voltages up to 550 kV and times to breakdown in the range 0.2-7 ??s. Whenever possible, the theory was checked against direct measurements and, considering the complexity of the problem, agreement is judged satisfactory.