BLOW-OPEN FORCES ON DOUBLE-BREAK CONTACTS

Measurements were made on double-break contact geometries, commonly us ed in power distribution devices, to determine contact dynamics under various short circuit fault conditions. These measurements lead to a m odification to improve contact dynamics during a short circuit. The mo dification consisted of a guide rod that prevented contact arm rotatio n during arcing. Contact dynamics depended on two blow-open forces, ma gnetic repulsion and gas pressure. Both forces were quantified for var ious double-break contact geometries along with arc voltage and contac t travel. The gas pressure, created by arc energy, was found to be a s ignificant blow-open force. Measured blow-open forces were compared to a sealed piston model to obtain an empirical equation for blow-open f orces. Contact performance was also determined with and without the gu ide rod for a range of arc currents.