Influence of the Contact Opening Speed on DC Vacuum Arc

Arc determines whether the vacuum switchgears can break current successfully, so it is significant to study its characteristics. In this paper, a hybrid high-speed actuator was designed, and a method of forced current zero was used to interrupt dc in a synthetic test circuit. With the different contact opening speeds, the processes of arc burning and current transferring were observed by a high-speed CMOS camera. Through the arc area obtained by an image processing technology, the influences of the opening speed on arc were researched, including the influences in the initial arc burning stage, in the forced current zero stage, and at the same electrode distance. The results indicate that with the increase of the opening speed in a certain range, the arc area in the forced current zero stage tends to be small, and the one in the initial arc burning stage spreads more quickly. Although the arc area increases with the opening speed in the initial arc burning stage, its impact on the whole dc current transferring process is slight when the contact opening speed is high. So, high opening speed is helpful to extinguish arc and transfer current. In addition, there is another discovery in the experiments. In a certain range, when the opening speed is higher, arc burns stably earlier, and the arc area is smaller in the stable burning stage. So, it is beneficial to inject the transferring current in this stage. Experimental results and analysis of the arc images prove that increasing the opening speed is useful to transfer the current successfully and recover the dielectric strength of the electrode distance.