Characteristic Parameters of the Anode Spot

In most of the works, the anode spot has been shown to be present whenever an electric arc occurs in the wake of an operating contactor, causing a slight contraction of the arc column. The role played by the anode is that of an electron collector, and it has now been acknowledged that the metal surface subjected to electron bombardment is unique with a circular shape. Starting from these hypotheses and using the laws of conservation at the level of the anode spot area, a theoretical model was set up enabling the following parameters to be stated for currents of average intensity (< 2000 A). r
_a
Spot radius. T
_a
Mean temperature. G
_a
Erosion speed. P
_a
Mean pressure. J
_ea
^'
Current total density. Jea Density of the emitted electron current. The system consisted of a set of six nonlinear equations; however, a numerical solution enabled the values of the six parameters to be stated for a given arc current I. Concerning copper or silver contacts, the results reported will be compared to experimental and theoretical works from other authors. The model proved valid through our own experiments, which showed the evolution of a metal surface subjected to an anode spot. In particular, mention will be made of the redeposition effect which enables the contactors to perform several million operations.