Thermal Arcs

Abstract

DC and AC arcs are governed essentially by the same basic features. The periodic change of the polarity at the line frequency in AC arcs obscure, however, the basic phenomena involved. Emphasis is therefore placed on DC arcs in this chapter which is divided into two principal section:The first deals with the arc column and the electrode regions. This includes the classical Elenbass-Heller model, which provides means for obtaining basic trends of arc column behavior such as the maximum temperature, which is feasible in an arc as function of the power input. This is followed by the Watson model, which represent a simple, single fluid description of an arc column. This section also covers a description of the electrode regions (Cathode and anode) and different current attachment mechanisms. The second part of this chapter is devoted to the current-voltage characteristics of arcs, and their electrical stability. A classification of the different methods used for stabilizing the arc column is presented. This includes free-burning arcs, self-stabilized arcs, gas – stabilized arcs, wall-stabilized arcs, vortex-stabilized arcs, electrode-stabilized arcs and finally magnetically stabilized arcs.