The repulsion of electrical contacts crossed by short-circuit currents

¹ Laboratoire de Génie Électrique de Paris, Plateau du Moulon, 91192 Gif-sur-Yvette, France
² Schneider Electric, 33 avenue du Maréchal Joffre, 92000 Nanterre Cedex, France

Corresponding author: teste@lgep.supelec.fr

Received: 3 April 2000
Revised: 20 October 2000
Accepted: 21 November 2000
Published online: 15 January 2001

Abstract

The study of forces exerted by an arc on silver-based electrical contacts is important in order to understand the dynamic phenomena concerning the opening or closing phases of contacts in a variety of switching applications. For that, an experimental device was built. It allows us to measure accurately the force on the static electrode and the displacement of the mobile electrode (and hence the force on it) when the two contacts, crossed by a current pulse (from 0 to 4 kA) separate. The measured forces are the sum of Lorentz magnetic forces (constriction force and loop effect force) and blow open forces due to the arc plasma (evaporation and (or) decomposition of contact 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 the contact material, the amplitude of the current pulse, the polarity of the 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 of the same order and that AgSnO₂ use allows to have higher forces (and longer opening phase) than for the two other materials and then may decrease the contact welding.