Electrical and photographic measurements of high-power arcs

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Abstract
The nature and behaviour of free-burning arcs between a graphite electrode and a molten steel pool at current levels up to 10 kA, rms, and associated powers of 1 MW, has been determined from electrical measurements and high-speed photographs. The dimensions, mobility and electrical properties of these arcs are reported for the half-cycles when the graphite electrode is cathode. Similar measurements were not possible for the alternate half-cycles because of the complex arc forms present. Some information of the velocities, electrical conductivity and energy-loss processes of these arcs was obtained by considering the steady-state characteristics in the electrode cathode half-cycles. It was concluded that the electrical conductivity was influenced, to a large extent, by the low ionization potential vapours evolved from the steel and graphite surfaces and that the main net energy loss from these arcs was by convection associated with the plasma jet streaming towards the steel surface, radiation playing a smaller but still significant role. Surprisingly, thermal conduction appears to be almost negligible as a mode of energy loss.

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