Experimental study on the transformation of the W₇₀Cu₃₀ anode erosion mode in DC gaseous arcs—better insights into mechanisms of electrode erosion behavior using in situ diagnosis

Abstract

This research concentrates on the erosion mechanism of the W 70 Cu 30 anode in DC gaseous arcs. An in situ diagnostic system including the measurement of the anode surface temperature and the fast-imaging of the erosion process was developed. The influence of gas media He, N 2 , H 2 , Ar and current, varying from 50 A to 400 A, was investigated. Two erosion modes were observed, namely an evaporation-dominated mode and a splash-dominated mode. The results indicate that the detachment of the splashing droplet is driven by the explosion of surface bubbles, and it is the surface temperature of the anode that determines the size of the surface bubble as well as the splashing erosion rate. Moreover, the prior vaporization of Cu dispersed in the W 70 Cu 30 anode limits the fusion of the W skeleton but promotes the generation of molten ejections by the explosions of Cu vapor bubbles when the topmost Cu is absent. The large difference between W and Cu in melting and boiling temperatures controls the formation of the molten pool on the W 70 Cu 30 anode and leads to the transition of the two erosion modes. The experimental results contribute to a fundamental understanding of the interaction between thermal plasmas and materials.

Evolution of anodic erosion components and heat transfer efficiency for W and W80Ag20 in atmospheric-pressure arcs

“…The splashing phenomenon in nitrogen is more obvious than in helium, but the sizes of splashing droplets are similar to that of in helium. In addition, continuous bubble explosion events (see red arrows in figure 6) on the anode tip can be found during the entire arcing discharge; such a phenomenon has been found with W 70 Cu 30 anode in our previous study [25]. However, the bubble explosion event appears more frequent with the W 80 Ag 20 anode, since several bubbles can be observed in one image, which has been rarely seen for the W 70 Cu 30 anode.…”

“…A 200 mm-focal-length macro lens coupled with a teleconverter was connected to the highspeed camera, which led to a spatial resolution of 12 µm/pixel. Detailed descriptions of this visualization method can be found in our previous works [25]. The surface temperature measurement was based on the two-color pyrometry.…”

“…This method consists of two main parts: (1) the 5 × 5 Laplacian edge detector for the identification of the splashing droplets [26], and (2) the modified particle matching algorithm [27] for the statistics of the splashing erosion. A detailed depiction of these two parts has been presented elsewhere [25].…”

“…The authors have initially proposed a visualization technique for the electrode erosion diagnosis in an air arc [24], which has been followed by the study of erosion mode transformation for the W 70 Cu 30 anode in different gaseous arcs [25]. Based on our previous work, this study is focused on the quantitative characterizations of the anodic erosion components and the heat transfer efficiency, in atmosphericpressure arcs with different plasma forming gases.…”

3D computational study of arc splitting during power interruption: the influence of metal vapor enhanced radiation on arc dynamics

“…Due to the high-current arc (over 10 kA) inducing a strong magnetic field, the saturation characteristic of ferromagnetic materials has a big influence on the arc splitting and requires further investigation. For metal vaporization, some progress has been made in the study of arcelectrode interactions [12][13][14][15][16], including the erosion mode (vaporization or splash) [13] and microcrater formation [17]. For example, some studies [17][18][19][20] investigated the microcrater formation on a cathode based on the ecton model with a pre-existing plasma.…”