Influence of contact geometry and current on effective erosion of Cu-Cr, Ag-WC, and Ag-Cr vacuum contact materials

Abstract

Effective ac erosion rates were measured for Cu-Cr, Ag-WC, and Ag-Cr butt-type contacts in vacuum contactors, using half-cycle current pulses of 450-600 A rms. The polarity was changed for each operation to ensure uniform effects for both contacts. The contacts parted during the rising current, with the full gap set to 10-30% of the contact diameter. The effective linear volume erosion rate [cm 3 /C] was determined by measuring the axial erosion of the contacts versus the number of operations. This was converted to an effective mass erosion rate [ g/C], which was significantly smaller than the reported absolute cathode erosion rate based on measured loss of cathode mass with long square current pulses at large fixed gap. The effective erosion rate increased when spiral-slotted contacts were used. The dependence of the effective erosion rate on the gap was studied, and also the distribution of metal droplets on the arc shield. Most of the droplet flux from the gap was close to the plane of the cathode, while a large fraction of the ionized vapor from the cathode spots was deposited onto the anode. The droplets were a significant fraction of the cathode material loss and the overall effective erosion.

The unusual electrical erosion of high tungsten content, tungsten copper contacts switching load current in vacuum

“…They also showed the effect of contact diameter, opening speed, contact structure and contact gap on the anode contact's ability to trap particles emitted from the cathode spot. The effective erosion rate was shown to be 0.20-0.33 of the absolute cathode spot erosion rate [2]. The studies also confirmed previous work on vacuum arc contact erosion [5], i.e., the erosion was mostly microparticles, and the maximum of the particle distribution was in the plane of the cathode contact.…”

“…Our effective mass erosion rates calculated in this way are slightly underestimated, since the small volume lost from erosion by cathode spots moving on the sides and backs of the contacts is not included. These data are shown in Table I together with comparable data from reference [2] for Cu-Cr and Ag-WC contacts. It can be seen that the volume erosion rate is two to three times higher and the mass erosion rate is about five times higher for the contacts used in the present experiments, compared to the erosion rates for the materials studied previously.…”

“…I N TWO previous papers [1], [2] we have presented the results of studies to determine the effective contact erosion rate that takes place in a vacuum interrupter switching a typical ac load current (200 A-1000 A). The contact materials used in these studies were Ag-WC, Cu-Cr, and Ag-Cr.…”

Properties of Nanocrystalline CuCr50 Contact Material

“…[4,5] Fibre reinforced syntactic foams with glass hollow micro spheres are investigated, too. [6] There are also studies about syntactic foams with hollow micro spheres in a metallic matrix. [ [**] The presented investigations were made within the current project IMVAL (Innovative Mineralschaum Verbund Applikationen für den Leichtbau).…”

“…Cathode erosion has always been an important and inevitable phenomenon in plasma science, which is consideresd as an unfavorable process that limits the lifetime of VIs. [6] Low erosion rate of nc-CuCr50 is highly advantageous to prolong the lifetime of VIs. Figure 4 shows the breakdown strength of the alloys as a function of breakdown number of both electrodes.…”