Nobuo Takatsu

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 m/s) precisely controlled make/break operation, contact voltage Vc and contact current Ic, residue of melt surface and discharge for breaking hinge relays with Ag contacting electrodes are measured. To control mechanical conditions, the movable electrode had a finely shaped convex surface (curvature radius: 0.5 mm) and a flat fixed electrode. Make/break operation was attempted only once due to transformation of contact surface. Then, Vc and Ic were measured at 1.5 to 25 V and 0.1 to 5 A. Fusion spots and residue of electric discharge on the contact surface were quantitatively measured using a laser microscope. Even when Vc and Ic were larger than the minimum arc voltage and minimum arc current, respectively, a continuous arc discharge occasionally did not occur. For the case of Vc=25 V and Ic=1 A, electric discharge was spontaneously suppressed to less than 100 s. The displacement of the movable electrode was estimated to be several nanometers for the discharging time interval. The residues of discharge were multiple damaged spots in the range of 100 m in radius, which had a black and/or white rectangular convex and concave shape.

Equivalent Circuit Analysis for Transient Phenomena from Elastic Contact to Breaking Contact through Metal Melting

This paper explores the proposal of equivalent circuits of electric breaking contacts to analyze the transient phenomena from elastic metal contact to rupture. The time dependency of elastic contact resistance is derived from the actual measurement values with the low current condition. The equivalent circuit for the phenomena is divided into the three stages: the first stage from the energizing to the softening voltage Us, the second stage from Us to the beginning of the latent heat, and the third stage from the start of the latent heat to the melting at the melting voltage Um. The accumulation of Joule heat at the contacts is shown with the capacitor in the circuits. The analytical result was able to qualitatively explain the complicated contact transient response characteristic of the Au crossing 1.0 mm φ rod experiment with source voltage 25 V, load current 2.5 A. Experimental results are compared with the fusion phenomena of conventional current fuse.