The appearance of vacuum arc is studied using an image sampling system with high speed. In the experiment
axial magnetic field contacts are used and the gap length changes from 10mm to 40mm. With the gap length increasing the area of arc spreading increases. At same arc current
the arc voltage is proportional to the gap length. With larger gap length the diffusing electrons
ions and metal material from arc column have an extra increase because of the adding surface of the arc column. The extra arc energy has to be afforded to heating the areas of contact