Velocity Distribution of the Moving Cathode Spot in Breaking Contact Arcs

The motion of cathode spot in Au, Ag, Cu, and Ni contacts, which affects the formation of the pip and crater structures, has been precisely observed by utilizing a high-speed camera in moderate current, atmospheric pressure dc break arcs. Dependencies of contact material, current and voltage on the motion of cathode spot were examined experimentally. Behaviors of the cathode spot were evaluated by three factors: 1) the maximum length moved (lmx) which was defined as a maximum shift distance of the spot in an arcing; 2) the maximum moving width (lmw) which was the difference between the maximum and minimum distances on the motion of cathode spot; and 3) distributions of velocity of moving cathode spot. For these contact materials, the cathode spot moved rapidly in the sequence of Au > Ag > Cu > Ni. Moreover, the crater structures of each contact have been reasonably explained through the above behavior of the cathode spot.