Researches on appearances change of vacuum switching arc in short-gap

Vacuum arc, as the key element of vacuum switches, is one of the important subjects in the field of high voltage apparatus. Researches on the basic theory of vacuum arc in short-gap have great influences on the development of intelligent vacuum circuit breakers and multiple-break vacuum circuit breakers. In order to do researches on the forms change of vacuum arc in short-gap, an experimental set-up based on vacuum circuit breakers´ model is designed in this paper. By using a high-speed CMOS digital video camera, images of vacuum arc can be observed during arcing in short-gap. At the same time, axial cross sectional area changing curve of the vacuum arc images is drawn with the aid of digital image processing technology, and the whole igniting process of vacuum arc can be divided into five stages by the observations: 1) initial stage, 2) diffusing stage I, 3) stable stage, 4) diffusing stage II, 5) quenching stage. In the end, combined the area changing curve and the arc images, the procedure of vacuum arc forms change is analyzed. From the results we can find the lasting time of arcing in the stages is 1.17ms, 1.83ms, 4.42ms, 1.81ms, 0.9ms respectively; and the increasing speed value of the arc area is about 3×10^-2 s^-1, 2×10^-2 s^-1, 0 s^-1, 2×10^-2 s^-1, 6×10^-2 s^-1 respectively.