High-speed observations of arc modes and material erosion on RMF- and AMF-contact electrodes

Vacuum interrupters, particularly with high short-circuit interruption ability, are mostly equipped with contact systems based on two different principles: the widely used radial magnetic field (RMF) contact and the axial magnetic field (AMF) contact system. In this investigation, contact electrodes performance of an improved RMF system was compared with both an unipolar and a quadrupolar AMF contact system. By using a high-speed complementary metal oxide semiconductor digital video camera, the different systems were observed during arcing under short-circuit conditions at different current levels, concentrating on arc modes development with different arcing times. Contact erosion and thermal. stress of the high-current vacuum arc on the contacts was basically evaluated on the basis of contact melting depth, with the result of comparable melting depths at insignificantly higher thermal stress of the RMF versus AMF systems. The microstructure of the copper and chromium compound contact material cross section was analyzed by means of a scanning electron microscope.