Generation of microparticles from copper-chromium contacts in vacuum

Using a scanning electron microscope (SEM) and a laser microscope, we observed micro-flakes and particles. On machined Cu-Cr contacts which were considered to be built-up edges due to machining. A large number of microparticles of 5.7-8.7×10³ from a contact surface of 1 cm², were generated from the machined Cu-Cr contacts during opening and closing operations of normal current. The size of typical microparticles was some tens μm and those larger than 100 μm were occasionally observed. This implies that the surface of machined Cu-Cr contacts must be treated by any means when they are used for vacuum interrupters. Current conditioning is one of the effective surface treatments. Although the surface roughness of the contacts increases through the current conditioning, the improvement of insulating ability is brought by the elimination of micro-flakes and particles and by the formation of a fine structure layer preventing partial detachment of the contact material