Melting Phenomena and Arc Ignition of Breaking Relay Contacts

Using the transient current switch circuit in parallel with the energizing switching contacts and the driving delay lines for timely control of breaking operations, the increase of contact voltage is suppressed as well as arc ignition at the last stage of the breaking electric contacts. Therefore, the melting phenomena can be slowly controlled and the electric characteristics can be accurately measured. Breaking contact voltage Vc and current Ic of conventional electromagnetic relays with Ag contacts were measured for two hinge springs (Spring constants; 2 N/mm and 0.2 N/mm), for 12.5~50 V energizing power-supply voltage and for 0.1~20 A contact current. The current-decreasing process was clearly measured at the melting voltage Um. After the melting voltage, the breaking time of contact current did not depend on mechanical conditions due to the two springs and energizing power-supply voltage, but did depend on the contact current. A new melting model of breaking mechanical contact is proposed. Using the model, a numerical equivalent circuit analysis of electric characteristics confirmed the measured data. For the conventional breaking operation (50 V/1A), arc ignition was measured after the melting break operation. The top of the metal contact had a finely shaped hemisphere and arc was ignited only once. The residue of arc ignition was observed as a black concentric circle, which was clearly separated from the melt contact point.