Breakdown in SF6 influenced by corona-stabilization

Corona-stabilization in SF₆-insulated systems is a known phenomenon, but up to now not fully understood. In case of slow-rising impulse voltage stress, a stabilization mechanism, mainly depending on the steepness of the applied test voltage, occurs. Essential for the phenomenon is a space-charge accumulation in front of the probe tip. The space charge reduces the field near the rod and thus an increased voltage level is needed to initiate the leader process. This paper presents experimental results. An imaging system consisting of 2 still-video CCD cameras has been used to record the paths of spark breakdowns across a positive point/plane gap. With subsequent computer image processing and analysis the dimension of the space-charge cloud could be estimated. Studies have been done for various probe tip lengths, gas pressures and steepnesses of the applied test voltage. The probability of corona-stabilization was determined for each test sequence. It was found that this probability decreases with the steepness of the applied test voltage for certain gas pressures