:The phenomenon of arcing is the major cause of electrical contact degradation in electrical switches. Degradation involves contact erosion and/or welding. The use of special contact material and that of specific material processing may permit contact erosion to be reduced, in particular by shortening the arc duration. A short review of these approaches is presented in the first part of this paper. In the second part, the development of a new self-blowing contact material is described. This material has been tested under DC voltages from 14 V to 42 V. A reduction of the arc duration by a factor of 4 approximately was obtained as was a concomitant reduction of the extinction gap to less than 2 mm. This material will contribute to achieving better reliability in high current-high voltages breaking devices, and will aid in their miniaturization, e.g. in relays.

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Erosion rate of electrical contacts is a very important parameter to understanding and evaluating the performances of contact materials and switching devices such as the life time. The most common measurement of arc erosion is the mass change of the contacts, determined by the weighing of the anode and the cathode, before and after the electrical tests. The erosion is well known to be a transfer from the anode to the cathode then from the cathode to the anode and finally a bilateral loss takes place. In this work, and to avoid the transfer phenomena, the mass of electrode after a large number of breaking operations is performed in the domain of bilateral erosion of the anode and cathode. Calculation of the evaporated mass by finite element simulation of thermal input and heat transfer to the electrode from the arc is made. It is found that the evaporated amount per unit of duration arc is in agreement for silver materials but for metal oxide it needs the knowledge of material properties and namely data of physical heat conduction.

The erosion of silver contacts due to break arcs with length proportional to time and of variable duration has been measured by weighing the contacts following 5000 openings at a constant current equal to 40 A. The experimental results show that, for arc durations shorter than 60 µs, the transfer of metal from the anode to the cathode occurs, but after passing this stage, when the two electrodes are separated by greater distances, each will display erosion. This is the result of the diffusion of material outside the space between the two electrodes. In order to interpret these results, we have applied a classical model of the physical phenomena occurring at the root of the arc. Analysis of the experimental results shows that for an arc duration of less than 15 µs, no distinct cathode root is seen to exist, but beyond this, several spots appear gradually on the cathode for arc duration up to 50 µs, after which they merge into a single spot. The comparison between experiment results and theoretical interpretation is reasonable up to 60 µs.

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