Effects of Cr content on the interruption ability of CuCr contact materials

The effects of Cr content in CuCr contact materials, especially on high current interruption, have mostly been examined in experimental chambers rather than in actual vacuum interrupters (VIs). Possible interactions of the contacts with their surroundings, both electromechanical and gaseous, may require commercial VIs for a more realistic test determination of the effects of Cr content on the overall performance. In this work, the Cr content in CuCr contacts is varied from 5 wt% to 75 wt% and tested in our 38-kV axial magnetic field (AMF) type VIs. The material properties of electrical conductivity, hardness and total VI resistance are measured as a function of the Cr content. AC and impulse voltage withstand capabilities are tested before and after short-circuit current interruption tests. Contact erosion behavior is examined with VIs subjected to only a half cycle arcing duty. Results show that for this particular AMF VI design, a 30 wt% Cr content gives the best current interruption performance.