Experimental investigation on the velocity of cathode spots in a vacuum arc with high di/dt

Abstract

With the development of DC transmission and aerospace technology, the demands on the breaking capacity of vacuum circuit breakers under high di/dt condition are getting higher and higher. The breaking capacity of vacuum circuit breakers is determined by cathode spots, which provide electrons and metal vapor to maintain the arc. In this paper, the experiments of cathode spot observation were carried out based on the detachable vacuum interrupter and the cup-shaped axial magnetic field contacts. The images of cathode spot distribution were obtained by an ultra high-speed camera. In the initial expansion stage of arcing, it was discovered that the distribution of cathode spots is ring-shaped and symmetrical. The initial expansion velocity of cathode spot ring is approximately proportional to the value of (di/dt)1/2 and is independent of frequency. During the whole arcing process, the expansion velocity of cathode spot ring rises first and then drops with arcing time. The effects of the magnetic field and metal vapor density on the expansion process of cathode spot were analyzed. Based on the experimental conditions and results, the values of magnetic field and metal vapor density were calculated which can reasonably explain the variation of expansion velocity of cathode spot.

Experimental study on dynamic characteristics of charged particles in vacuum arc

“…According to equation (12), the toroidal magnetic field can promote particle diffusion, while the axial magnetic field can inhibit particle diffusion. The variation curves of axial magnetic field, toroidal magnetic field and metal vapor pressure with time were given in [36],which was shown in figure 12. The axial magnetic field intensity is proportional to the current, and the toroidal magnetic field intensity is related to the current and arc radius.…”

Dynamic characteristics of cathode spots during expansion process in a vacuum arc

“…The magnetic field is an important factor that changes the behavior of ions and also directly affects the generation of cathode spot. In our previous work, the effects of AMF and TMF on the expansion velocity of cathode spot were studied [12]. The conclusion is that the TMF which is generated by the arc current contributes to the generation of new cathode spot.…”

“…Besides TMF, axial magnetic field (AMF) is also important for the distribution of cathode spots. Several previous experimental research has dealt with the investigation of the behavior of cathode spot in a axial magnetic field [11][12][13][14]. It was discovered that the AMF constrains radial expansion of cathode spots.…”