Short Vacuum Arc Research Articles

Cathode processes in free burning and stabilized by axial magnetic field vacuum arcs

Collective behavior of the cathode spots (CS) has been investigated in free burning and stabilized by axial magnetic field (AMF) vacuum arcs. Experiments carried out proved previously discovered phenomenon of CS group formation in free burning arc to be a general phenomenon for a short high-current vacuum arc. The dependency of CS group size in the developed are on arc current for different contact materials has been analyzed. Application of AMF with even relatively low intensity strongly affects on cathode processes. In short arcs, it hinders formation of the CS group and consequently reduces thermal stress applied to the electrodes. It has been revealed that high current vacuum arc under the action of AMF can exist only at current densities exceeding certain minimal value that depends on AMF intensity, contact gap, and does not depend on current itself. The dependency of this minimal (or normal) current density on AMF intensity has been studied for short and long vacuum arcs. A qualitative model of the cathode spot dynamics has also been proposed.

The short vacuum arc. II. Model and theoretical aspects

For pt.I see ibid., vol.16, no.3, p.342-7, June 1988. A physical model is presented of the development of a short cathode-anode vacuum arc, from the moment of electrode separation to the final state, a cathode-autonomous vacuum arc. Although the highly nonstationary initial phase is accessible only to qualitative reasoning, the analysis of the stationary arc is treated quantitatively, accounting for anode influence using an existence diagram. The cathode-autonomous phase is previously known in the literature. Results for the phase transitions, arc appearance, and arc motion agree qualitatively with previous observations (reported in Part I). >

The short vacuum arc. I. Experimental investigations

High-current vacuum arcs drawn between commercial radial-magnetic field, chromium-copper contacts were studied by high-speed photography. The aim of the investigation was to study phenomena of relevance to high-current interruption, such as arc constriction and arc motion. The arcs were drawn at contact opening speeds typical of commercial devices, are duration being 10 ms or less. The arcs were 'short' for much of their lifetime, and strong electrode-discharge coupling could be expected. Such arcs are also of principal interest. Arc behavior was found to be strongly influenced by the gap length d and the arc current I. No diffuse mode was observed at d less the d/sub min/ approximately=4 mm and at instantaneous currents I above I/sub max/+or-25 kA. The diffuse discharge mode was assumed more readily when d was large. At d below 2 mm, the arcs could not be moved by a magnetic field. Increasing both I and d resulted in an increase of the probability and duration of arc motion and of the arc path length. Arc speed was often irregular, showing that arc motion is also affected by parameters other than the purely electrodynamic ones. >