Development of a simple procedure for screening current interruption capability of vacuum interrupter contact materials

A simple testing procedure has been developed in order to investigate and screen the current interruption capability of vacuum interrupter contact materials. A synthetic circuit delivering adjustable AC currents, followed by a pulsed of 21 kV peak for 2 seconds has been used. The electrical tests has been developed to reproduce the conditions close to a fault current rated at 12 kV; only the recovery voltage is a bit tougher in the present set-up. Specially prepared vacuum interrupters with selected contact materials have been stressed in a single pole with this electrical set-up: current is increased by steps until three straight failures occur. This defines the highest current interruption performance of the contact material under investigation. The presented procedure is quick (less than one day per material composition), cheap and the results straightforward to analyze. Comparisons with a 3-phase test in a power laboratory for some of the contact materials have been performed; the obtained results are in the window of uncertainty of the simple testing procedure, thus validating the new approach for research and development purpose. In the second part of this paper, the results of the contact materials tested with the help of this procedure are presented Various contact materials based on CuCr 25 have been investigated, as well as materials with more chromium content (CuCr 30 and CuCr 35). The interruption capability shows a maximum for CuCr 25, and a slight decrease of the performance with the increase in chromium content. A contact material based on CuCr 25 with a high content of molybdenum reveals extremely reduced current interruption capability.