Electric Measurement of Melting Phenomena for Breaking Relay Contacts

Using the transient current switch circuit in parallel with the energizing switching contacts for timely control of breaking operation, the increase of contact voltage is suppressed at the last stage of the breaking of electric contacts. Breaking contact voltage V c and current I c of electromagnetic relays with Ag contacting electrodes were measured with 12.5-50 V and 0.1-20 A for two hinge springs (Spring constants; 2 N/mm and 0.2 N/mm). The current-decreasing process was clearly measured at the melting voltage U m . After V c = U m , the breaking time of contact current did not depend on mechanical motion controlled by the two hinge springs and energizing power-supply voltage, but depended on the contact current. The residue of melt electrode was observed optically as a white fusion spot, with radius depending on the energizing current.