The vacuum arc and vacuum interruption

The vacuum arc has been widely studied in recent years. One of the principal reasons for this interest has been the increasing use of the vacuum arc to achieve circuit interruption in electrical distribution systems. This is an expanding application with sales predictions of 300000 units for 1987 and with many millions already in service worldwide. Despite this interest, it is still true to say there remain considerable gaps in understanding of the physics of the vacuum arc. One of the principal reasons for this is the practical difficulties of carrying out experimental investigations. For example, cathode emitting sites in the vacuum arc are small mobile zones of high charge-carrier densities with high electric and magnetic fields, rendering them extremely difficult to investigate. In addition, there are considerable practical difficulties linked with the preparation of contact surfaces and with the dispersion of the results. The object of this paper is twofold. Firstly, to review the present state of understanding of the physical processes in the vacuum arc, including the arc structure, cathode spot, interelectrode plasma and current-zero phenomena. Secondly, this paper will also consider in general terms the nature of the application of vacuum interruption, and the implications for interrupter design.