Prebreakdown emission current measurements in a 24 kV vacuum interrupter with butt contacts

Commercial 24-kV vacuum interrupters with butt contacts were tested under DC conditions with three different contact materials: OFHC-copper, stainless steel 304 and Cu/Cr (75/25, wt.%). The critical breakdown field was computed at contact distances of 1, 2 and 3 mm, based on the prebreakdown emission current and the breakdown voltage. While the values for the critical breakdown field for OFHC-copper and stainless steel 304 were in agreement with the values found by other authors, no previous data were found for Cu/Cr.<>