High-current graphite cathode free-burning arcs

Ultra-high-current arcs (I<25 kA) have been studied under pulsed (10¿20ms duration) laboratory conditions in order to indicate the energy transfer processes which will be of importance in a.c. arc furnaces. Measurements have been obtained of a number of the fundamental parameters of free-burning arcs having truncated conical graphite cathodes. Total arc voltage and arc current were measured, the results indicating a high degree of arc stability. This stability, which was confirmed by a high-speed photographic survey, enabled the axial electric field to be determined from probe measurements of the voltage distribution within the arc gap. Column radiation losses also were found as a function of axial position and time, and the importance of radiation losses as a power-dissipation mechanism was examined both locally, i.e. axially, and for the total gap. Comparisons of these various measurements with those of other workers are made, with particular reference to laboratory arc furnace studies. The importance of axial convection arising from magnetic pumping at the cathode may be inferred, in agreement with the findings of studies at lower current levels.