Modeling and simulation of vacuum arc under the influence of anode melting pool

With advancements in vacuum technology, the application range of vacuum circuit breakers which have excellent properties such as strong breaking ability, maintenance-free life and pollution-free has gradually expanded to high-voltage applications. When a vacuum circuit breaker breaks a high current, the vacuum arc type changes from diffusion to agglomeration. The energy transported from the arc column to the anode increases as the arc current and anode temperature increase to surpass the melting point of the anode material. Under extreme circumstances, an anode melting pool is formed; this influences the properties of the vacuum arc plasma between the electrodes and inhibits the strength recovery of the insulating medium, which increases the likelihood of breaking failure. This study developed a magnetohydrodynamic (MHD) model to simulate and analyze properties of a high-current vacuum arc after formation of an anode melting pool. Different ablation conditions of the anode surface after the actual arc are analyzed by changing the anode boundary shape in the arc plasma simulation area. Results demonstrate that pressure distributions of vacuum arc plasma are independent of the depth, diameter, and distance of the anode melting pool. The maximum pressure increases with the increase in the arc current value and is affected by the edge bumps of the melting pool. The maximum temperature of the vacuum arc plasma correlates positively with the arc current, the melting pool depth and diameter, and the distance between electrodes, but is independent of the presence of a melting pool on the cathode surface. These research results can not only enrich the theory of vacuum breaking, but also provide the theoretical basis for improvement and development of vacuum circuit breaker.

I. Introduction

Vacuum arcs have played extremely important roles in many fields, such as vacuum ion sources [1], vacuum extinguishing chambers [2], and vacuum arc thrusters [3]. Vacuum circuit breakers, which have many advantages such as small size, light weight, strong breaking capacity, maintenance-free during their lifetime, suitable for frequent operations, and environmentally friendly, have been widely used in modern low- and medium-voltage power distribution fields [4]. In the early stage of vacuum circuit breaker breaking, the arc current is concentrated in a small area of the contact, the resistance increases, and a large amount of Joule heat is generated. As the arc current increases and the energy flow density converges towards the center of the arc, the anode temperature rises and eventually melts to form a melting poo1 [5]. The anode melting pool will affect the density of metal vapor after the arc passes zero. If the residual charge density is higher than the critical value, the arc will reignite, resulting in vacuum circuit breaker breaking failure [6]. Therefore, it is more conducive to reveal the internal physical process of its breaking by simulation and emulation, and it is easier to measure the distribution of its microscopic physical characteristic parameters. This can accurately predict the breaking performance of vacuum circuit breakers and provide a theoretical basis for improving and developing new types of vacuum circuit breakers.