Investigation on the Thermal Process of Anode in Vacuum Arc

Abstract

SUMMARY Anode activity in vacuum arc plays a very important rolein both characteristics of vacuum arc and the interruption capacity of vac-uum interrupters. In this paper, the transient thermal processes of anodein vacuum arc in a half of arc current cycle with frequency of 50Hz aresimulated by finite element analysis software, ANSYS. Some importantphenomena of anode, e.g., the melt and solidification, mass loss due toevaporation, are investigated. key words: vacuum arc, anode, melt, evaporation, finite element analysis 1. Introduction Electric arc burning between the electrodes of vacuumswitches is distinct from other gas arc, e.g., air arc, and sul-phur hexafluoride (SF6) arc, due to its special arcing en-vironment, vacuum. In gas arc, arc plasma comes mainlyfrom ionized gas molecule, whereas, arc plasma of vac-uum arc can only originate from electrodes. At low cur-rent, arc plasma is supplied by cathode spots, predominately,whereas, anode acts only as a passive particle collecter.However, with the increase of arc current, both plasma flowand current flow tend to constrict inward near anode sur-face under the influence of self-generated azimuthal mag-netic field. The constriction of vacuum arc leads to the en-ergy flux density flowing into anode increase locally. Asa result, local temperature of anode will increase that maycause melt, even evaporation of anode, which has signifi-cant influence on the characteristic of arc plasma, and playsthe vital role in arc reignition after current zero.Thermal process of either cathode or anode, e.g., spottemperature, erosion rate, composition and influence of ero-sion products, has been substantially investigated, experi-mentally, whereas, most theoretical models focus on cath-ode spots [1],[2]. Concerning the thermal processes of an-ode, following theoretical researches should be reviewed.Parkansky et al.[3] adopted the integral conservationlaws in a limiting case. Anode erosion rate at low current(200–400A) was investigated under different pressure byconsidering the distribution of energy dissipation in differentcases. Since this model is essentially in steady-state equilib-rium, time-dependent parameters can’t be got.In the work of Beilis [4], a relatively complex one-dimension (1-D) model was developed for anode spot region