Influence of Impurities on the Interruption Performance of Solid State Sintered CuCr25

A wide variety of solid state sintered CuCr25 contact material is studied in detail and metallurgical aspects will be discussed down to sub micrometric scale. Nano-metric sized Chromium Oxide particles are found around Chromium particles in the Copper matrix. Their interruption performance in Axial Magnetic Field Vacuum Interrupters (VI's) is studied. The materials are tested as 22 mm diameter flat contacts in an asymmetrical VI with external axial magnetic field coil. Tests are performed at a short circuit current of 10 kA rms in a strong AMF (15 mT/kA) and at a recovery voltage of 17 kV (TRV peak 29 kV). Short circuit interruption performance was highly dependent on the material parameters. Two failure modes are identified: Failure due to late breakdowns and failure in the thermal interruption phase. The influence of impurities on both breakdowns will be discussed. The latter seems to be related to chromium linked impurities.