Takayuki Kudo

Melting and Discharge Phenomena of Breaking Ag Contacts Using a Precisely Controlled Piezoelectric Actuator

Using a laminated ceramic piezoelectric actuator for a very slow (4.5 µm/s) precisely controlled make/break operation, the contact voltage Vc, the contact current Ic, and the amounts of residue of the melt and discharged surface and discharge for breaking hinge relays with Ag-contacting electrodes were measured. To control mechanical conditions, we used a movable electrode with a finely shaped convex surface (radius of curvature: 0.5 mm) and a flat fixed electrode. Every make/break operation causes surface irregularity. Therefore, the operation was performed only once. In order to measure the area of the contacted surface after metal melting and arc ignition, Vc and Ic was adjusted to be 25 V and 1.2 A, respectively. Even when Vc and Ic were larger than the minimum arc voltage and minimum arc current, respectively, electric discharge was spontaneously suppressed below 130 µs. The residues of discharge were multiple scars with radii in the range of 100 µm, which had a black and/or white rectangular convex or concave shape.

Melting phenomena of electric contacts during current interruption

The physical phenomena related to the melting of electric contacts are classified and the relations to electric characteristics are examined. The solid phase and/or the liquid phase exist at melting temperature. Joule heats from the electric circuit accumulate the latent heat till the melting of the contacts. We studied how the phase changes are ruled by electric circuit. The melting phenomena at the contact current interruption were observed electrically and optically.