Optical Investigations of High-Current Vacuum Arc Behavior on Spiral-Shaped and Cup-Shaped RMF-Contacts

Vacuum circuit breakers are mostly equipped with radial magnetic field (RIM F) contacts forcing the electric arc on a circular motion by a self-induced magnetic field. Using a high-speed-camera with a recording rate above 25,000 frames per second the appearance of vacuum arcs was investigated from two 90 degrees displaced views regarding three different contact designs with CuCr 75/25 as contact material. Spiral shaped contacts and cup-shaped contacts with diameter of 68 mm and 65 mm, respectively, and spiral shaped contacts with diameter of 90 mm were investigated with 45 Hz short-circuit currents of amplitudes up to 85 kA. From the high-speed films arc motion, shape and velocity as well as current density were determined in consideration of arc voltage and current strength. Results were compared to former publications.