Observation of Metallurgical Changes Induced by an Electric Arc on Ag-SnO2-CuO Electrodes

Understanding the erosion of contact materials caused by electric arcs is a major challenge to improve the lifetime of switching devices. The main purpose of this study is to determine how the silver-tin oxide material (Ag-SnO
₂
12%w.-CuO, sintered) evolves under the action of a unique arc and multiple arcs (up to 50,000). Pairs of electrodes were submitted to an opening arc at room atmosphere for current intensity of 150, 300 and 600 A rms and typical duration of 4 ms. Different means of characterization were used: optical microscopy, optical profilometry, energy dispersive spectroscopy (EDS) of the electrode surface, electron backscatter diffraction (EBSD). For a unique arc, it was possible to observe a resolidified molten zone and estimate its dimensions. The influence of the number of arcs has been studied and a gradual evolution of the damage nature has been demonstrated as a function of the arc numbers.