Blow-open forces on double-break contacts

Measurements were made on a double-break contact geometries, commonly used in power distribution devices, to determine contact dynamics under various short circuit fault conditions. These measurements lead to a modification to improve contact dynamics during a short circuit. The modification consisted of a guide-rod which prevented contact arm rotation during arcing. Contact dynamics depended on two blow-open forces, magnetic repulsion and gas pressure. Both forces were quantified for various double-break contact geometries along with arc voltage and contact travel. The gas pressure, created by arc radiation, was found to be a significant blow-open force. Measured blow-open forces were compared to a sealed piston model to obtain an empirical equation for blow-open forces. Contact performance was also determined with and without the guide-rod for a range of arc currents.