Arcing at Electrical Contacts on Closure. Part VI. The Anode Mechanism of Extremely Short Arcs

Abstract

The erosion at the anode of a short arc has been studied as a function of the arc duration and the magnitude of the arc current. With the current maintained at a constant value the anode pit grows continuously in diameter up to a critical value of the order of 10 microns; when this size is reached, a new arc is initiated and a new pit starts to develop. The process may be repeated. Consideration of the heat loss from the anode shows that for a constant arc power the pressure of metal vapor between the electrodes is very sensitive to the area covered by the arc. An order of magnitude estimate of the minimum metal vapor pressure required to maintain the arc (∼100 atmospheres) yields a value of the maximum pit diameter in good agreement with the experimental observations. It is evident that the steady‐state short arc does not exist, and quantities such as the metal transfer, ion to electron current ratio, and pressure in the arc are dependent on the time since the initiation of the arc.