Model switch experiments for determining the evolution of contact resistance of electrical contacts in contactors

As a first step in a long-term planned cooperation between the TU Ilmenau and several industry partners a model switch was developed and constructed in order to investigate the influence of different aspects affecting the evolution of contact resistance during the lifetime of electrical contacts in low voltage contactors. The device permits, besides the variation of different geometrical and kinetic parameters, the determination of the contact resistance by different contact closing forces. Several material analysis methods, such as laser surface profilometry, light microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were applied to Ag/Ni10 contacts before and after experimental series with breaking AC-arcs according to IEC 60947. Important information regarding surface structure, chemical composition and formed crystalline phases of the surface contact materials and ambient materials were obtained. The main characteristics of the model switch and some results of the first experiments are presented in this paper.