The diploma work deals with the phenomena during switching the low voltage electrical circuit depending on the material of the electrical contact surface as well as changes in the microstructure in the contact material after braking the electrical circuit with high current and low voltage. As the contact material pure deoxidized copper and tinned pure deoxidized copper have been chosen and investigated. The phenomena occurring in the initial stage of making the electrical contact include contact surfaces bouncing, the evaporation, ionization, and transfer of material between the contact surfaces, the formation of arcs and the consequent formation of welds of the contact surfaces.
We used an electronic oscilloscope to detect the occurrence of contact surface bounces, by measuring the voltage change during the initial stage of establishing the electrical contact. In this way, we could determine how many times contact surfaces bounced between each other and how the material of the contact surface influences the time required to completely establish the electrical circuit. We also designed a device for bridging high-current through a contact assembly, which simulated events at such high currents that caused contact surfaces to be welded and the switch destroyed. Because we were interested in the specific properties of both types of materials, we also measured the UI characteristic during breaking the electrical contact. Microstructural changes in the contact material were also analyzed with light and electron microscope after breaking the high current electrical circuit.