Research on the influence of grain size of CuCr contact on the characteristics of cathode spot and cathode surface erosion in vacuum arc

CuCr alloy is widely used in vacuum interrupters. The characteristics of cathode spot and erosion of cathode surface directly affects the lifetime and breaking capacity of vacuum interrupter. In order to control the cathode spot and crater, two types of contacts with different Cr phase size were used in this paper. The vacuum arc breaking experiments were conducted. The cathode spot images were recorded by ultra high speed camera and craters were measured by Scanning Electron Microscope and Profiler. It was found that the smaller the Cr phase size, the higher the expansion velocity of cathode spots, the larger the number of cathode spot, the smaller the cathode spot size and the lower the current carried by each cathode spot. The reduction of Cr phase size helps to improve the uniform distribution of cathode spots on the contact surface. Besides, the smaller Cr phase size leads to the decrease of radius and depth of crater. For CuCr contacts, thermal diffusion process was analyzed and there is a significant difference in the thermal diffusivity between Cu and Cr. The Cr phase uniformly distributed in Cu prevents the thermal diffusion process which reduces the size of crater and the erosion of cathode surface.