Electrical and Morphological Investigations of Electrical Contacts used in Low-Voltage Circuit-Breakers

The contact point in modular protective devices is the place where the current lines are concentrated. This phenomenon leads to the contact point heating or even melting, with a risk of sticking. Sticking can prevent the product from opening if the opening force is not sufficient to detach the contacts, causing serious damage to the electrical installation and to persons. It is therefore essential to avoid any welding of the contacts. That is why a test bench was designed and built in order to determine the temperature rise and the conditions leading to static melting. The current used had a waveform and an amplitude similar to that of the short-circuit current.This paper presents electrical measurements coupled with microscopic measurements of contact surfaces: 3D optical imaging (x500), and electron imaging (x150 to 2000) for surface topology and chemical distribution. This allowed us to better interpret the electrical behavior of the contact point. Investigations were performed according to several parameters: current amplitude passing through the contact point and contact force preset via a spring. Based on the results, the influence of these parameters on the contact voltage and on the state of the contact surface was characterized.