TIME CURRENT CHARACTERISTICS AND BREAKING CAPACITY OF EXPERIMENTAL VACUUM FUSES

Conventional HV fuses are filled with quartz sand. They have an excell ent current-limiting capability, however, they have a zone of an uncer tain operation in the low overcurrent range. To overcome this disadvan tage, considerations were made to substitute the quartz sand by vacuum . The background of these considerations was the well known excellent arc quenching capability of vacuum switches at current zero. Thus the historical development of the vacuum fuse was strongly influenced by p rogress in the field of vacuum switches. A vacuum fuse can be designed by inserting a fusible element between the fixed butt contacts (elect rodes) of a vacuum chamber. Melting curves and the arc quenching capab ility at current zero are investigated for a simply designed vacuum fu se with flat contacts. Variables are the current amplitude, the electr ode material, the diameter of the fuse wire and the distance between t he electrodes.