The repulsion of electrical contacts crossed by short-circuit currents

The study of forces exerted by an arc on silver-based electrical contacts i s important in order to understand the dynamic phenomena concerning the ope ning or closing phases of contacts in a variety of switching applications. For that, an experimental device was built. It allows us to measure accurat ely the force on the static electrode and the displacement of the mobile el ectrode (and hence the force on it) when the two contacts, crossed by a cur rent pulse (from 0 to 4 kA) separate. The measured forces are the sum of Lo rentz magnetic forces (constriction force and loop effect force) and blow o pen forces due to the arc plasma (evaporation and (or) decomposition of con tact materials). A simple method allowed us to asses the value of the blow open forces. We have also studied the influence on the measured forces of t he contact material, the amplitude of the current pulse, the polarity of th e electrodes. For the electrode materials tested in this study (Ag-SnO2, Ag -CdO and Ag-CW), it appeared that forces exerted on cathode and anode are o f the same order and that AgSnO2 use allows to have higher forces (and long er opening phase) than for the two other materials and then may decrease th e contact welding.