Abstract:

To clarify the evolution law of metallic liquid bridges and the inducing mechanism of double liquid bridges during the contact separation process of DC miniature circuit breakers(MCB), a slow-breaking experimental platform equipped with a high-power electron microscope is established. Taking copper(Cu) and CuCr0.5 alloy as contact materials, the characteristics of metallic liquid bridges are systematically investigated under the conditions of DC 13 V load, current ranging from 16 A to 22 A, and breaking speed between 0.4 mm/s and 1.0 mm/s, with the synchronous collection of geometric parameters and waveform data. The results show that the evolution of liquid bridges undergoes three stages:heating and melting, stable existence, and unstable rupture. The stable liquid bridge presents a cylindrical shape; after rupture, a needle-shaped residue forms on the cathode, and the material migrates directionally from the anode to the cathode. The size of liquid bridges increases with the rise of current and decreases with the increase of breaking speed. An increase in current tends to induce double liquid bridges, and their rupture is prone to trigger arc discharge. The CuCr0.5 alloy contacts completely suppress the occurrence of double liquid bridges, exhibiting significantly superior resistance to liquid bridges and arc discharge compared with pure copper contacts.

Key words: DC miniature circuit breaker, metallic liquid bridge, slow breaking, CuCr0.5 alloy, double liquid bridge