Photographic study of discharge development and high-current arc modes in vacuum

Photographic studies of discharge development and arc modes were done for high-current arcs between cup (contrate) contacts at a fixed contact gap (10 mm). The peak value of the applied AC arc current half-wave ranged from a few kA to 24 kA. Photographs of the arc were taken with a high-speed framing camera at 10000 frames/s. Three main arc modes are distinguished: diffuse; diffuse with local discharge concentrations near the electrode, and constricted with a stationary anode spot. The authors showed a tendency of the anode spot to locate inside the cup. This effect is typical for various sorts of contacts with cup. The authors stressed the harmful influence of the constricted arc with a stationary anode spot in the bottom of the cup on current interrupting and magnetic fields generation by the contrate contact