Zhiyuan Liu

TL;DR: In this article, the authors investigated the high-current vacuum arc phenomena of a nanocrystalline CuCr25 (Cr 25 wt%) contact material, and the results showed that both the arc energy and the mean value of the arc voltage of the nano-copper contact material were lower than those of the micro-crystalline one under the same experimental conditions.

TL;DR: In this paper, a discharge and breakdown mechanism transition in the conditioning process was proposed, and three pairs of plane-plane copper electrodes machined by diamond turning were designed, and X-ray photo-electron spectroscopy (XPS) was performed to analyze the surface of the electrodes.

Abstract: Microparticles produced by high current vacuum arcs significantly reduce the insulation performance of vacuum interrupters. The objective of this paper is to observe the generation and dynamics of microparticles during the arcing and post-arcing period, and to further reveal the possible effects of particles during interruption of a high current vacuum arc. A plasma diagnosis system based on a laser-shadow technique was used to measure the particles in a demountable vacuum chamber. The results show that contact materials affect particle generation patterns. For a CuCr contact with a higher proportion of chromium, the formation of a melting pool is much more difficult and the flow of liquid metal on the surface can be suppressed, which also impedes the formation of particles. Moreover, reignition after arc extinction was found to be triggered by some incandescent particles. These hot particles have two effects on breakdown events during the post-arcing phase: they trigger a micro-discharge between a particle and the electrode, and new weak points are left on the surface that enhance the local field. More crucially, the lifetime of spontaneous particles spans up to hundreds of milliseconds after current zero, which indicates that long-delayed breakdown is correlated with the existence of particles. In addition, some particles could remain suspended near the electrode or oscillate between the contacts. The dynamic behavior of these particles can significantly lower the breakdown threshold and increase the possibility of breakdown.

TL;DR: In this article, a model of fluid flow and heat transfer in the arc anode is developed and combined with a magnetohydrodynamics model of the vacuum arc plasma, and the condition for the liquid droplet formation on the anode surfaces is developed.