Arc commutation in low voltage circuit breakers: Influence of the electrical contact materials

The success of the interrupt process appearing in a low voltage breaking device is closely linked to the quality of current transfer between the arc and the electrodes. The breaking device has to minimise the thermal constraint and the energy dissipated during the arc life time. The best way to reach this aim is to cause the arc extinction as soon as possible. The arc has then to leave the moving contacts quickly, but it should above all not re- ignite between these contacts, because in this case all the commutation phase restarts and the time necessary for the arc extinction increases. The arc reignition depends on both electric field and gas residual conductivity in the contacts area. The electric field is linked to the arc voltage and also to the arc dynamic during the commutation. The gas residual conductivity is influenced by the quantity of vaporized conductive material. In order to understand phenomena involved in the arc extinction, several contact materials have been experimentally tested in this study. Electrical quantities have been measured or deduced from measurements, and magnetic measurements have been exploited by an inverse method and compared with information given by an ultra fast optical camera.