Electrical Properties of Nanocrystalline CuCr25 Contact Material

Four pieces of nanocrystalline CuCr25 contacts with 45-mm diameter and 3-mm thickness were prepared, brazed onto cup-axial magnetic field electrodes, and assembled in two commercial vacuum interrupters to test their chopping current, ac dielectric breakdown voltage, and breaking capacity. For comparison, two microcrystalline CuCr25 contacts were also prepared as above. The test vacuum interrupters were operated by a 24-kV circuit breaker with a spring-operated mechanism. The opening velocity was 1.3 m/s and the arc current frequency was about 50 Hz. The experimental results showed that both the chopping current and the ac dielectric breakdown voltage of nanocrystalline CuCr25 contact material were lower than those of the microcrystalline CuCr25 material. The breaking capacity of nanocrystalline CuCr25 material was significantly lower than that of microcrystalline CuCr25. The cathode and the anode contact surfaces of nanocrystalline CuCr25 were seriously eroded by arc in the local areas, and obvious cracks occurred.