Interfacial layer as an evaluation criterion of electrical contacts

Stationary switch contacts of practical applications may present nonlinear current voltage behaviour and phase shift effects. These phenomena are related to the appearance of tunnelling currents in the interfacial layer at high electric fields. In the paper experimental data are presented, and a theoretical investigation is attempted concerning these phenomena. The results lead to a new method for the quality evaluation of stationary electrical contacts. This method is based on measurements of the voltage drop waveforms on contacts under test. From the experimental and theoretical results, it can be concluded that the operation of adequately oxidised contacts (in a state of degradation) appears to be improved when they are strained for a short time period by current values greater than the nominal ones. This can be attributed to the breakdown of the interfacial layer as impact ionisation occurs, and new paths through metallic spots are created