Testing procedure for the current interruption capability of vacuum interrupter contact materials

A testing procedure has been developed with the aim to investigate and to screen the current interruption capability of vacuum interrupters with different contact materials. A synthetic circuit delivering a 1.2 ms pulse current up to 18 kA was used in order to simulate a surface temperature on the electrodes similar to the constricted arc mode. At current zero a pulse voltage was injected to stress the vacuum interrupters to a value corresponding to the peak transient voltage of a 24 kV rating. Vacuum interrupters with contact materials based on CuCr 75/25 wt% were tested in a single phase. The statistical analysis of the probability of current interruption failure as a function of the current allowed ranking the contact materials compared to a commercial CuCr 75/25 wt% used as a reference. A specially doped CuCr 75/25 wt% showed higher potential current interruption capability than the reference, while the other contacts produced from different copper and chromium powders´ suppliers had similar current interruption capability than the reference. The trend given by this method has been compared with results obtained in a three-phase test at a power laboratory. The test procedure is able to predict the major trends, but lacks of sensitivity for the small composition differences. In addition, it was found that when using the best materials in vacuum interrupters rated 20 kA/12 kV a potential current interruption capability higher than 33 kA would be in principle possible based on the contact material only.