Study of the influence of the electrode gap on contact material erosion (Cu, Ag and AgMeO) in air and argon at atmospheric pressure

摘要

Erosion measurements on electrical contacts generally found in the literature include several causes of erosion. Indeed, in addition to the electrode matter removal purely due to the arc root action, those measurements include erosion caused by the molten bridge explosion and often by matter wrenching due to welding phenomena during contact rebounds. It was important to separate the erosion caused only by the arc root for an electrode gap d fixed at a constant value for the all arc duration. In the same way, always with d as a parameter, we observed the erosion evolution with a cover gas. In order to simultaneously, increase the validity of the study and to considerably simplify the interpretation of the experimental results, an original experimental device have been elaborated. This device is able to create, in a first time, a short glow discharge between two electrodes at a fixed distance d apart and then to generate rectangular arc current pulses. The results have shown a strong dependence of electrode erosion on electrode gap particularly in air for all the contact materials tested. In pure argon, we noted also a dependence of electrode erosion on d, for pure materials, but for the AgMeO pseudo alloys, the tests have shown a very weak erosion. Consequently in air for instance, and for all the electrode materials tested, the erosion rate expressed in μg.C~(-1) becomes strongly gap dependant and therefore does not present a great practical and physical significance. We note a maximum of erosion for pure materials (in air and argon) and composite materials (in air) for small d and high d respectively. Then, we present, always for a constant electrode gap, the variation of the erosion versus the oxygen volumes fraction x of a mixture O_(2x)Ar_(1-x). The results of this mixture gas show a minimum of electrode erosion for the anode and cathode.